Chemical Composition of Galactic Disk Stars

NASA Astrophysics Data System (ADS)

Mishenina, T. V.; Basak, N. Yu.; Gorbaneva, T. I.; Soubiran, C.; Kovtyukh, V. V.

Abundances of Na, Al, Ca, in the stars of galactic disks are obtained. The separation of thin and stars on cinematic criterion was made early. The behavior of chemical element abundances with metallicity for studied stars was presented.

An ultra-relativistic outflow from a neutron star accreting gas from a companion.

PubMed

Fender, Rob; Wu, Kinwah; Johnston, Helen; Tzioumis, Tasso; Jonker, Peter; Spencer, Ralph; Van Der Klis, Michiel

2004-01-15

Collimated relativistic outflows-also known as jets-are amongst the most energetic phenomena in the Universe. They are associated with supermassive black holes in distant active galactic nuclei, accreting stellar-mass black holes and neutron stars in binary systems and are believed to be responsible for gamma-ray bursts. The physics of these jets, however, remains something of a mystery in that their bulk velocities, compositions and energetics remain poorly determined. Here we report the discovery of an ultra-relativistic outflow from a neutron star accreting gas within a binary stellar system. The velocity of the outflow is comparable to the fastest-moving flows observed from active galactic nuclei, and its strength is modulated by the rate of accretion of material onto the neutron star. Shocks are energized further downstream in the flow, which are themselves moving at mildly relativistic bulk velocities and are the sites of the observed synchrotron emission from the jet. We conclude that the generation of highly relativistic outflows does not require properties that are unique to black holes, such as an event horizon.

On the Progenitor of Binary Neutron Star Merger GW170817

NASA Astrophysics Data System (ADS)

Abbott, B. P.; Abbott, R.; Abbott, T. D.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X.; Adya, V. B.; Affeldt, C.; Afrough, M.; Agarwal, B.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O. D.; Aiello, L.; Ain, A.; Ajith, P.; Allen, B.; Allen, G.; Allocca, A.; Altin, P. A.; Amato, A.; Ananyeva, A.; Anderson, S. B.; Anderson, W. G.; Angelova, S. V.; Antier, S.; Appert, S.; Arai, K.; Araya, M. C.; Areeda, J. S.; Arnaud, N.; Arun, K. G.; Ascenzi, S.; Ashton, G.; Ast, M.; Aston, S. M.; Astone, P.; Atallah, D. V.; Aufmuth, P.; Aulbert, C.; AultONeal, K.; Austin, C.; Avila-Alvarez, A.; Babak, S.; Bacon, P.; Bader, M. K. M.; Bae, S.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Banagiri, S.; Barayoga, J. C.; Barclay, S. E.; Barish, B. C.; Barker, D.; Barkett, K.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barta, D.; Bartlett, J.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Bawaj, M.; Bayley, J. C.; Bazzan, M.; Bécsy, B.; Beer, C.; Bejger, M.; Belahcene, I.; Bell, A. S.; Berger, B. K.; Bergmann, G.; Bero, J. J.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Billman, C. R.; Birch, J.; Birney, R.; Birnholtz, O.; Biscans, S.; Biscoveanu, S.; Bisht, A.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blackman, J.; Blair, C. D.; Blair, D. G.; Blair, R. M.; Bloemen, S.; Bock, O.; Bode, N.; Boer, M.; Bogaert, G.; Bohe, A.; Bondu, F.; Bonilla, E.; Bonnand, R.; Boom, B. A.; Bork, R.; Boschi, V.; Bose, S.; Bossie, K.; Bouffanais, Y.; Bozzi, A.; Bradaschia, C.; Brady, P. R.; Branchesi, M.; Brau, J. E.; Briant, T.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brockill, P.; Broida, J. E.; Brooks, A. F.; Brown, D. D.; Brunett, S.; Buchanan, C. C.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cabero, M.; Cadonati, L.; Cagnoli, G.; Cahillane, C.; Calderón Bustillo, J.; Callister, T. A.; Calloni, E.; Camp, J. B.; Canepa, M.; Canizares, P.; Cannon, K. C.; Cao, H.; Cao, J.; Capano, C. D.; Capocasa, E.; Carbognani, F.; Caride, S.; Carney, M. F.; Casanueva Diaz, J.; Casentini, C.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C. B.; Cerdá-Durán, P.; Cerretani, G.; Cesarini, E.; Chamberlin, S. J.; Chan, M.; Chao, S.; Charlton, P.; Chase, E.; Chassande-Mottin, E.; Chatterjee, D.; Cheeseboro, B. D.; Chen, H. Y.; Chen, X.; Chen, Y.; Cheng, H.-P.; Chia, H.; Chincarini, A.; Chiummo, A.; Chmiel, T.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Q.; Chua, A. J. K.; Chua, S.; Chung, A. K. W.; Chung, S.; Ciani, G.; Ciolfi, R.; Cirelli, C. E.; Cirone, A.; Clara, F.; Clark, J. A.; Clearwater, P.; Cleva, F.; Cocchieri, C.; Coccia, E.; Cohadon, P.-F.; Cohen, D.; Colla, A.; Collette, C. G.; Cominsky, L. R.; Constancio, M., Jr.; Conti, L.; Cooper, S. J.; Corban, P.; Corbitt, T. R.; Cordero-Carrión, I.; Corley, K. R.; Corsi, A.; Cortese, S.; Costa, C. A.; Coughlin, M. W.; Coughlin, S. B.; Coulon, J.-P.; Countryman, S. T.; Couvares, P.; Covas, P. B.; Cowan, E. E.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Creighton, J. D. E.; Creighton, T. D.; Cripe, J.; Crowder, S. G.; Cullen, T. J.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dal Canton, T.; Dálya, G.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Dasgupta, A.; Da Silva Costa, C. F.; Dattilo, V.; Dave, I.; Davier, M.; Davis, D.; Daw, E. J.; Day, B.; De, S.; DeBra, D.; Degallaix, J.; De Laurentis, M.; Deléglise, S.; Del Pozzo, W.; Demos, N.; Denker, T.; Dent, T.; De Pietri, R.; Dergachev, V.; De Rosa, R.; DeRosa, R. T.; De Rossi, C.; DeSalvo, R.; de Varona, O.; Devenson, J.; Dhurandhar, S.; Díaz, M. C.; Di Fiore, L.; Di Giovanni, M.; Di Girolamo, T.; Di Lieto, A.; Di Pace, S.; Di Palma, I.; Di Renzo, F.; Doctor, Z.; Dolique, V.; Donovan, F.; Dooley, K. L.; Doravari, S.; Dorrington, I.; Douglas, R.; Dovale Álvarez, M.; Downes, T. P.; Drago, M.; Dreissigacker, C.; Driggers, J. C.; Du, Z.; Ducrot, M.; Dupej, P.; Dwyer, S. E.; Edo, T. B.; Edwards, M. C.; Effler, A.; Eggenstein, H.-B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Eisenstein, R. A.; Essick, R. C.; Estevez, D.; Etienne, Z. B.; Etzel, T.; Evans, M.; Evans, T. M.; Factourovich, M.; Fafone, V.; Fair, H.; Fairhurst, S.; Fan, X.; Farinon, S.; Farr, B.; Farr, W. M.; Fauchon-Jones, E. J.; Favata, M.; Fays, M.; Fee, C.; Fehrmann, H.; Feicht, J.; Fejer, M. M.; Fernandez-Galiana, A.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Finstad, D.; Fiori, I.; Fiorucci, D.; Fishbach, M.; Fisher, R. P.; Fitz-Axen, M.; Flaminio, R.; Fletcher, M.; Fong, H.; Font, J. A.; Forsyth, P. W. F.; Forsyth, S. S.; Fournier, J.-D.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Frey, V.; Fries, E. M.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Gabbard, H.; Gadre, B. U.; Gaebel, S. M.; Gair, J. R.; Gammaitoni, L.; Ganija, M. R.; Gaonkar, S. G.; Garcia-Quiros, C.; Garufi, F.; Gateley, B.; Gaudio, S.; Gaur, G.; Gayathri, V.; Gehrels, N.; Gemme, G.; Genin, E.; Gennai, A.; George, D.; George, J.; Gergely, L.; Germain, V.; Ghonge, S.; Ghosh, Abhirup; Ghosh, Archisman; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gill, K.; Glover, L.; Goetz, E.; Goetz, R.; Gomes, S.; Goncharov, B.; Gonzalez Castro, J. M.; Gopakumar, A.; Gorodetsky, M. L.; Gossan, S. E.; Gosselin, M.; Gouaty, R.; Grado, A.; Graef, C.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Green, A. C.; Gretarsson, E. M.; Groot, P.; Grote, H.; Grunewald, S.; Gruning, P.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Halim, O.; Hall, B. R.; Hall, E. D.; Hamilton, E. Z.; Hammond, G.; Haney, M.; Hanke, M. M.; Hanks, J.; Hanna, C.; Hannam, M. D.; Hannuksela, O. A.; Hanson, J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M. J.; Haster, C.-J.; Haughian, K.; Healy, J.; Heidmann, A.; Heintze, M. C.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Hennig, J.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hinderer, T.; Hoak, D.; Hofman, D.; Holgado, A. M.; Holt, K.; Holz, D. E.; Hopkins, P.; Horst, C.; Hough, J.; Houston, E. A.; Howell, E. J.; Hreibi, A.; Hu, Y. M.; Huerta, E. A.; Huet, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh-Dinh, T.; Indik, N.; Inta, R.; Intini, G.; Isa, H. N.; Isac, J.-M.; Isi, M.; Iyer, B. R.; Izumi, K.; Jacqmin, T.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jiménez-Forteza, F.; Johnson, W. W.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; Junker, J.; Kalaghatgi, C. V.; Kalogera, V.; Kamai, B.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Kapadia, S. J.; Karki, S.; Karvinen, K. S.; Kasprzack, M.; Katolik, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kawabe, K.; Kéfélian, F.; Keitel, D.; Kemball, A. J.; Kennedy, R.; Kent, C.; Key, J. S.; Khalili, F. Y.; Khan, I.; Khan, S.; Khan, Z.; Khazanov, E. A.; Kijbunchoo, N.; Kim, Chunglee; Kim, J. C.; Kim, K.; Kim, W.; Kim, W. S.; Kim, Y.-M.; Kimball, C.; Kimbrell, S. J.; King, E. J.; King, P. J.; Kinley-Hanlon, M.; Kirchhoff, R.; Kissel, J. S.; Kleybolte, L.; Klimenko, S.; Knowles, T. D.; Koch, P.; Koehlenbeck, S. M.; Koley, S.; Kondrashov, V.; Kontos, A.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Krämer, C.; Kringel, V.; Królak, A.; Kuehn, G.; Kumar, P.; Kumar, R.; Kumar, S.; Kuo, L.; Kutynia, A.; Kwang, S.; Lackey, B. D.; Lai, K. H.; Landry, M.; Lang, R. N.; Lange, J.; Lantz, B.; Lanza, R. K.; Larson, S. L.; Lartaux-Vollard, A.; Lasky, P. D.; Laxen, M.; Lazzarini, A.; Lazzaro, C.; Leaci, P.; Leavey, S.; Lee, C. H.; Lee, H. K.; Lee, H. M.; Lee, H. W.; Lee, K.; Lehmann, J.; Lenon, A.; Leonardi, M.; Leroy, N.; Letendre, N.; Levin, Y.; Li, T. G. F.; Linker, S. D.; Littenberg, T. B.; Liu, J.; Lo, R. K. L.; Lockerbie, N. A.; London, L. T.; Lord, J. E.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J. D.; Lousto, C. O.; Lovelace, G.; Lück, H.; Lumaca, D.; Lundgren, A. P.; Lynch, R.; Ma, Y.; Macas, R.; Macfoy, S.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magaña Hernandez, I.; Magaña-Sandoval, F.; Magaña Zertuche, L.; Magee, R. M.; Majorana, E.; Maksimovic, I.; Man, N.; Mandic, V.; Mangano, V.; Mansell, G. L.; Manske, M.; Mantovani, M.; Marchesoni, F.; Marion, F.; Márka, S.; Márka, Z.; Markakis, C.; Markosyan, A. S.; Markowitz, A.; Maros, E.; Marquina, A.; Martelli, F.; Martellini, L.; Martin, I. W.; Martin, R. M.; Martynov, D. V.; Mason, K.; Massera, E.; Masserot, A.; Massinger, T. J.; Masso-Reid, M.; Mastrogiovanni, S.; Matas, A.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McCuller, L.; McGuire, S. C.; McIntyre, G.; McIver, J.; McManus, D. J.; McNeill, L.; McRae, T.; McWilliams, S. T.; Meacher, D.; Meadors, G. D.; Mehmet, M.; Meidam, J.; Mejuto-Villa, E.; Melatos, A.; Mendell, G.; Mercer, R. A.; Merilh, E. L.; Merzougui, M.; Meshkov, S.; Messenger, C.; Messick, C.; Metzdorff, R.; Meyers, P. M.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, A. L.; Miller, B. B.; Miller, J.; Millhouse, M.; Milovich-Goff, M. C.; Minazzoli, O.; Minenkov, Y.; Ming, J.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moffa, D.; Moggi, A.; Mogushi, K.; Mohan, M.; Mohapatra, S. R. P.; Montani, M.; Moore, C. J.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mours, B.; Mow-Lowry, C. M.; Mueller, G.; Muir, A. W.; Mukherjee, Arunava; Mukherjee, D.; Mukherjee, S.; Mukund, N.; Mullavey, A.; Munch, J.; Muñiz, E. A.; Muratore, M.; Murray, P. G.; Napier, K.; Nardecchia, I.; Naticchioni, L.; Nayak, R. K.; Neilson, J.; Nelemans, G.; Nelson, T. J. N.; Nery, M.; Neunzert, A.; Nevin, L.; Newport, J. M.; Newton, G.; Ng, K. K. Y.; Nguyen, T. T.; Nichols, D.; Nielsen, A. B.; Nissanke, S.; Nitz, A.; Noack, A.; Nocera, F.; Nolting, D.; North, C.; Nuttall, L. K.; Oberling, J.; O'Dea, G. D.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Okada, M. A.; Oliver, M.; Oppermann, P.; Oram, Richard J.; O'Reilly, B.; Ormiston, R.; Ortega, L. F.; O'Shaughnessy, R.; Ossokine, S.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pace, A. E.; Page, J.; Page, M. A.; Pai, A.; Pai, S. A.; Palamos, J. R.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, Howard; Pan, Huang-Wei; Pang, B.; Pang, P. T. H.; Pankow, C.; Pannarale, F.; Pant, B. C.; Paoletti, F.; Paoli, A.; Papa, M. A.; Parida, A.; Parker, W.; Pascucci, D.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Patil, M.; Patricelli, B.; Pearlstone, B. L.; Pedraza, M.; Pedurand, R.; Pekowsky, L.; Pele, A.; Penn, S.; Perez, C. J.; Perreca, A.; Perri, L. M.; Pfeiffer, H. P.; Phelps, M.; Piccinni, O. J.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pirello, M.; Pitkin, M.; Poe, M.; Poggiani, R.; Popolizio, P.; Porter, E. K.; Post, A.; Powell, J.; Prasad, J.; Pratt, J. W. W.; Pratten, G.; Predoi, V.; Prestegard, T.; Prijatelj, M.; Principe, M.; Privitera, S.; Prodi, G. A.; Prokhorov, L. G.; Puncken, O.; Punturo, M.; Puppo, P.; Pürrer, M.; Qi, H.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raja, S.; Rajan, C.; Rajbhandari, B.; Rakhmanov, M.; Ramirez, K. E.; Ramos-Buades, A.; Rapagnani, P.; Raymond, V.; Razzano, M.; Read, J.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Ren, W.; Reyes, S. D.; Ricci, F.; Ricker, P. M.; Rieger, S.; Riles, K.; Rizzo, M.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V. J.; Romano, R.; Romel, C. L.; Romie, J. H.; Rosińska, D.; Ross, M. P.; Rowan, S.; Rüdiger, A.; Ruggi, P.; Rutins, G.; Ryan, K.; Sachdev, S.; Sadecki, T.; Sadeghian, L.; Sakellariadou, M.; Salconi, L.; Saleem, M.; Salemi, F.; Samajdar, A.; Sammut, L.; Sampson, L. M.; Sanchez, E. J.; Sanchez, L. E.; Sanchis-Gual, N.; Sandberg, V.; Sanders, J. R.; Sassolas, B.; Sathyaprakash, B. S.; Sauter, O.; Savage, R. L.; Sawadsky, A.; Schale, P.; Scheel, M.; Scheuer, J.; Schmidt, J.; Schmidt, P.; Schnabel, R.; Schofield, R. M. S.; Schönbeck, A.; Schreiber, E.; Schuette, D.; Schulte, B. W.; Schutz, B. F.; Schwalbe, S. G.; Scott, J.; Scott, S. M.; Seidel, E.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sequino, V.; Sergeev, A.; Shaddock, D. A.; Shaffer, T. J.; Shah, A. A.; Shahriar, M. S.; Shaner, M. B.; Shao, L.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Shoemaker, D. M.; Siellez, K.; Siemens, X.; Sieniawska, M.; Sigg, D.; Silva, A. D.; Singer, L. P.; Singh, A.; Singhal, A.; Sintes, A. M.; Slagmolen, B. J. J.; Smith, B.; Smith, J. R.; Smith, R. J. E.; Somala, S.; Son, E. J.; Sonnenberg, J. A.; Sorazu, B.; Sorrentino, F.; Souradeep, T.; Spencer, A. P.; Srivastava, A. K.; Staats, K.; Staley, A.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stevenson, S. P.; Stone, R.; Stops, D. J.; Strain, K. A.; Stratta, G.; Strigin, S. E.; Strunk, A.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sunil, S.; Suresh, J.; Sutton, P. J.; Swinkels, B. L.; Szczepańczyk, M. J.; Tacca, M.; Tait, S. C.; Talbot, C.; Talukder, D.; Tanner, D. B.; Tápai, M.; Taracchini, A.; Tasson, J. D.; Taylor, J. A.; Taylor, R.; Tewari, S. V.; Theeg, T.; Thies, F.; Thomas, E. G.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thrane, E.; Tiwari, S.; Tiwari, V.; Tokmakov, K. V.; Toland, K.; Tonelli, M.; Tornasi, Z.; Torres-Forné, A.; Torrie, C. I.; Töyrä, D.; Travasso, F.; Traylor, G.; Trinastic, J.; Tringali, M. C.; Trozzo, L.; Tsang, K. W.; Tse, M.; Tso, R.; Tsukada, L.; Tsuna, D.; Tuyenbayev, D.; Ueno, K.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Valdes, G.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; Van Den Broeck, C.; Vander-Hyde, D. C.; van der Schaaf, L.; van Heijningen, J. V.; van Veggel, A. A.; Vardaro, M.; Varma, V.; Vass, S.; Vasúth, M.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Venugopalan, G.; Verkindt, D.; Vetrano, F.; Viceré, A.; Viets, A. D.; Vinciguerra, S.; Vine, D. J.; Vinet, J.-Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Vyatchanin, S. P.; Wade, A. R.; Wade, L. E.; Wade, M.; Walet, R.; Walker, M.; Wallace, L.; Walsh, S.; Wang, G.; Wang, H.; Wang, J. Z.; Wang, W. H.; Wang, Y. F.; Ward, R. L.; Warner, J.; Was, M.; Watchi, J.; Weaver, B.; Wei, L.-W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Wessel, E. K.; Weßels, P.; Westerweck, J.; Westphal, T.; Wette, K.; Whelan, J. T.; Whiting, B. F.; Whittle, C.; Wilken, D.; Williams, D.; Williams, R. D.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M. H.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Woehler, J.; Wofford, J.; Wong, K. W. K.; Worden, J.; Wright, J. L.; Wu, D. S.; Wysocki, D. M.; Xiao, S.; Yamamoto, H.; Yancey, C. C.; Yang, L.; Yap, M. J.; Yazback, M.; Yu, Hang; Yu, Haocun; Yvert, M.; Zadrożny, A.; Zanolin, M.; Zelenova, T.; Zendri, J.-P.; Zevin, M.; Zhang, L.; Zhang, M.; Zhang, T.; Zhang, Y.-H.; Zhao, C.; Zhou, M.; Zhou, Z.; Zhu, S. J.; Zhu, X. J.; Zucker, M. E.; Zweizig, J.; (LIGO Scientific Collaboration; Virgo Collaboration

2017-12-01

On 2017 August 17 the merger of two compact objects with masses consistent with two neutron stars was discovered through gravitational-wave (GW170817), gamma-ray (GRB 170817A), and optical (SSS17a/AT 2017gfo) observations. The optical source was associated with the early-type galaxy NGC 4993 at a distance of just ˜40 Mpc, consistent with the gravitational-wave measurement, and the merger was localized to be at a projected distance of ˜2 kpc away from the galaxy’s center. We use this minimal set of facts and the mass posteriors of the two neutron stars to derive the first constraints on the progenitor of GW170817 at the time of the second supernova (SN). We generate simulated progenitor populations and follow the three-dimensional kinematic evolution from binary neutron star (BNS) birth to the merger time, accounting for pre-SN galactic motion, for considerably different input distributions of the progenitor mass, pre-SN semimajor axis, and SN-kick velocity. Though not considerably tight, we find these constraints to be comparable to those for Galactic BNS progenitors. The derived constraints are very strongly influenced by the requirement of keeping the binary bound after the second SN and having the merger occur relatively close to the center of the galaxy. These constraints are insensitive to the galaxy’s star formation history, provided the stellar populations are older than 1 Gyr.

Searching for dark matter with neutron star mergers and quiet kilonovae

NASA Astrophysics Data System (ADS)

Bramante, Joseph; Linden, Tim; Tsai, Yu-Dai

2018-03-01

We identify new astrophysical signatures of dark matter that implodes neutron stars (NSs), which could decisively test whether NS-imploding dark matter is responsible for missing pulsars in the Milky Way galactic center, the source of some r -process elements, and the origin of fast-radio bursts. First, NS-imploding dark matter forms ˜10-10 solar mass or smaller black holes inside neutron stars, which proceed to convert neutron stars into ˜1.5 solar mass black holes (BHs). This decreases the number of neutron star mergers seen by LIGO/Virgo (LV) and associated merger kilonovae seen by telescopes like DES, BlackGEM, and ZTF, instead producing a population of "black mergers" containing ˜1.5 solar mass black holes. Second, dark matter-induced neutron star implosions may create a new kind of kilonovae that lacks a detectable, accompanying gravitational signal, which we call "quiet kilonovae." Using DES data and the Milky Way's r-process abundance, we constrain quiet kilonovae. Third, the spatial distribution of neutron star merger kilonovae and quiet kilonovae in galaxies can be used to detect dark matter. NS-imploding dark matter destroys most neutron stars at the centers of disc galaxies, so that neutron star merger kilonovae would appear mostly in a donut at large radii. We find that as few as ten neutron star merger kilonova events, located to ˜1 kpc precision could validate or exclude dark matter-induced neutron star implosions at 2 σ confidence, exploring dark matter-nucleon cross-sections 4-10 orders of magnitude below current direct detection experimental limits. Similarly, NS-imploding dark matter as the source of fast radio bursts can be tested at 2 σ confidence once 20 bursts are located in host galaxies by radio arrays like CHIME and HIRAX.

X-ray spectra and atmospheric structures of bursting neutron stars

NASA Technical Reports Server (NTRS)

Ebisuzaki, Toshikazu

1987-01-01

Atmospheric structures and emitted X-ray spectra of bursting neutron stars are investigated. Theoretical curves are fitted to observational ones on the color temperature vs. luminosity diagram and two relations among mass, radius, and distance of the bursters are obtained. The fit of the theoretical curve to observations is statistically acceptable. Two possible sets of mass, radius, and distance to the X-ray bursts source MXB 1636-536 are derived, taking into account absorption lines at 4.1 keV, theoretical mass-radius relations of neutron star models, and the distance to the Galactic center. If the absorption line is due to Cr XX III, then M = 1.7-2.0 solar masses, R = 11-12 km, and d = 6.3-6.7 kpc, and if it is due to Fe XXV, then M = 1.8-2.1 solar masses, R = 8-10 km, and d = 5.8-6,4 kpc. The distance to the Galactic center is almost the same as that to MXB 1636-536.

Unusual Metals in Galactic Center Stars

NASA Astrophysics Data System (ADS)

Hensley, Kerry

2018-03-01

Far from the galactic suburbs where the Sun resides, a cluster of stars in the nucleus of the Milky Way orbits a supermassive black hole. Can chemical abundance measurements help us understand the formation history of the galactic center nuclear star cluster?Studying Stellar PopulationsMetallicity distributions for stars in the inner two degrees of the Milky Way (blue) and the central parsec (orange). [Do et al. 2018]While many galaxies host nuclear star clusters, most are too distant for us to study in detail; only in the Milky Way can we resolve individual stars within one parsec of a supermassive black hole. The nucleus of our galaxy is an exotic and dangerous place, and its not yet clear how these stars came to be where they are were they siphoned off from other parts of the galaxy, or did they form in place, in an environment rocked by tidal forces?Studying the chemical abundances of stars provides a way to separate distinct stellar populations and discern when and where these stars formed. Previous studies using medium-resolution spectroscopy have revealed that many stars within the central parsec of our galaxy have very high metallicities possibly higher than any other region of the Milky Way. Can high-resolution spectroscopy tell us more about this unusual population of stars?Spectral Lines on DisplayTuan Do (University of California, Los Angeles, Galactic Center Group) and collaborators performed high-resolution spectroscopic observations of two late-type giant starslocated half a parsec from the Milky Ways supermassive black hole.Comparison of the observed spectra of the two galactic center stars (black) with synthetic spectra with low (blue) and high (orange) [Sc/Fe] values. Click to enlarge. [Do et al. 2018]In order to constrain the metallicities of these stars, Do and collaborators compared the observed spectra to a grid of synthetic spectra and used a spectral synthesis technique to determine the abundances of individual elements. They found that

Star formation around active galactic nuclei

NASA Technical Reports Server (NTRS)

Keel, William C.

1987-01-01

Active galactic nuclei (Seyfert nuclei and their relatives) and intense star formation can both deliver substantial amounts of energy to the vicinity of a galactic nucleus. Many luminous nuclei have energetics dominated by one of these mechanisms, but detailed observations show that some have a mixture. Seeing both phenomena at once raises several interesting questions: (1) Is this a general property of some kinds of nuclei? How many AGNs have surround starbursts, and vice versa? (2) As in 1, how many undiscovered AGNs or starbursts are hidden by a more luminous instance of the other? (3) Does one cause the other, and by what means, or do both reflect common influences such as potential well shape or level of gas flow? (4) Can surrounding star formation tell us anything about the central active nuclei, such as lifetimes, kinetic energy output, or mechanical disturbance of the ISM? These are important points in the understanding of activity and star formation in galactic nuclei. Unfortunately, the observational ways of addressing them are as yet not well formulated. Some preliminary studies are reported, aimed at clarifying the issues involved in study of the relationships between stellar and nonstellar excitement in galactic nuclei.

Modeling the Spin Equilibrium of Neutron Stars in LMXBs Without Gravitational Radiation

NASA Technical Reports Server (NTRS)

Andersson, N.; Glampedakis, K.; Haskell, B.; Watts, A. L.

2004-01-01

In this paper we discuss the spin-equilibrium of accreting neutron stars in LMXBs. We demonstrate that, when combined with a naive spin-up torque, the observed data leads to inferred magnetic fields which are at variance with those of galactic millisecond radiopulsars. This indicates the need for either additional spin-down torques (eg. gravitational radiation) or an improved accretion model. We show that a simple consistent accretion model can be arrived at by accounting for radiation pressure in rapidly accreting systems (above a few percent of the Eddington accretion rate). In our model the inner disk region is thick and significantly sub-Keplerian, and the estimated equilibrium periods are such that the LMXB neutron stars have properties that accord well with the galactic millisecond radiopulsar sample. The implications for future gravitational-wave observations are also discussed briefly.

Molecular diagnostics of Galactic star-formation regions

NASA Astrophysics Data System (ADS)

Loenen, Edo; Baan, Willem; Spaans, Marco

2007-10-01

We propose a sensitive spectral survey of Galactic star-formation regions. Using the broadband correlator at two different frequencies, we expect to detect the (1-0) transition of CO, CN, HNC, HCN, HCO+, and HCO and various of their isotopes lines, as well as the (12-11) and (10-9) transitions of HC3N. The purpose of these observations is to create a consistent (public) database of molecular emission from galactic star-formation regions. The data will be interpreted using extensive physical and chemical modeling of the whole ensemble of lines, in order to get an accurate description of the molecular environment of these regions. In particular, this diagnostic approach will describe the optical depths, the densities, and the radiation fields in the medium and will allow the establishment of dominant temperature gradients. These observations are part of a program to study molecular emission on all scales, going from individual Galactic star-formation regions, through resolved nearby galaxies, to unresolved extra-galactic emission.

The Galactic O-Star Catalog (GOSC) and the Galactic O-Star Spectroscopic Survey (GOSSS): current status

NASA Astrophysics Data System (ADS)

Maíz Apellániz, J.; Alonso Moragón, A.; Ortiz de Zárate Alcarazo, L.; The Gosss Team

2017-03-01

We present the updates of the Galactic O-Star Catalog (GOSC) that we have undertaken in the last two years: new spectral types, more objects, additional information, and coordination with CDS. We also present updates for the Galactic O-Star Spectroscopic Survey (GOSSS). A new paper (GOSSS-III) has been published and ˜ 1000 targets have been observed since 2014. Four new setups have been added to our lineup and for two of them we have already obtained over 100 spectra: with OSIRIS at the 10.4 m GTC we are observing northern dim stars and with FRODOspec at the 2.0 m Liverpool Telescope we are observing northern bright stars. Finally, we also make available new versions of MGB, the spectral classification tool associated with the project, and of the GOSSS grid of spectroscopic standards.

The Galactic Chemical Evolution of r-Process Elements by Neutron Star Mergers

NASA Astrophysics Data System (ADS)

Komiya, Yutaka; Shigeyama, Toshikazu

Neutron star mergers (NSMs) are prime candidate sources of r-process elements in the universe but it have been said that NSMs cannot reproduce r-process elements on extremely metal-poor (EMP) stars. We revisit this problem using a new chemical evolution model with merger trees of galaxies. We consider (1) propagation of NSM ejecta of kilo-parsec scale due to its very large velocity and (2) star formation efficiency depending on the galaxy mass. In our model with these ingredients, NSMs can successfully reproduce the abundance distribution of EMP stars.

Galactic Winds and the Role Played by Massive Stars

NASA Astrophysics Data System (ADS)

Heckman, Timothy M.; Thompson, Todd A.

Galactic winds from star-forming galaxies play at key role in the evolution of galaxies and the intergalactic medium. They transport metals out of galaxies, chemically enriching the intergalactic medium and modifying the chemical evolution of galaxies. They affect the surrounding interstellar and circumgalactic media, thereby influencing the growth of galaxies though gas accretion and star formation. In this contribution we first summarize the physical mechanisms by which the momentum and energy output from a population of massive stars and associated supernovae can drive galactic winds. We use the prototypical example of M 82 to illustrate the multiphase nature of galactic winds. We then describe how the basic properties of galactic winds are derived from the data, and summarize how the properties of galactic winds vary systematically with the properties of the galaxies that launch them. We conclude with a brief discussion of the broad implications of galactic winds.

Converting neutron stars into strange stars

NASA Technical Reports Server (NTRS)

Olinto, A. V.

1991-01-01

If strange matter is formed in the interior of a neutron star, it will convert the entire neutron star into a strange star. The proposed mechanisms are reviewed for strange matter seeding and the possible strange matter contamination of neutron star progenitors. The conversion process that follows seeding and the recent calculations of the conversion timescale are discussed.

Introduction to neutron stars

NASA Astrophysics Data System (ADS)

Lattimer, James M.

2015-02-01

Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts can set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.

Introduction to neutron stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lattimer, James M.

Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts canmore » set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.« less

A Formation Timescale of the Galactic Halo from Mg Isotopes in Dwarf Stars

NASA Astrophysics Data System (ADS)

Carlos, Marília; Karakas, Amanda I.; Cohen, Judith G.; Kobayashi, Chiaki; Meléndez, Jorge

2018-04-01

We determine magnesium isotopic abundances of metal-poor dwarf stars from the galactic halo, to shed light on the onset of asymptotic giant branch (AGB) star nucleosynthesis in the galactic halo and constrain the timescale of its formation. We observed a sample of eight new halo K dwarfs in a metallicity range of ‑1.9 < [Fe/H] < ‑0.9 and 4200 < T eff(K) < 4950, using the HIRES spectrograph at the Keck Observatory (R ≈ 105 and 200 ≤ S/N ≤ 300). We obtain magnesium isotopic abundances by spectral synthesis on three MgH features and compare our results with galactic chemical evolution models. With the current sample, we almost double the number of metal-poor stars with Mg isotopes determined from the literature. The new data allow us to determine the metallicity when the 26Mg abundances start to become important, [Fe/H] ∼ ‑1.4 ± 0.1. The data with [Fe/H] > ‑1.4 are somewhat higher (1–3σ) than previous chemical evolution model predictions, indicating perhaps higher yields of the neutron-rich isotopes. Our results using only AGB star enrichment suggest a timescale for formation for the galactic halo of about 0.3 Gyr, but considering also supernova enrichment, the upper limit for the timescale formation is about 1.5 Gyr. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Conversion of gas into stars in the Galactic center

NASA Astrophysics Data System (ADS)

Longmore, S. N.

2014-05-01

The star formation rate in the central 500 pc of the Milky Way is lower by a factor of > 10 than expected for the substantial amount of dense gas it contains, which challenges current star formation theories. I discuss which physical mechanisms could be causing this observation and put forward a self-consistent cycle of star formation in the Galactic center, in which the plausible star formation inhibitors are combined. Their ubiquity suggests that the perception of a lowered central SFR should be a common phenomenon in other galaxies with direct implications for galactic star formation and also potentially supermassive black hole growth. I then describe a scenario to explain the presence of super star clusters in the Galactic center environment, in which their formation is triggered by gas streams passing close to the minimum of the global Galactic gravitational potential at the location of the central supermassive black hole, Sgr A*. If this triggering mechanism can be verified, we can use the known time interval since closest approach to Sgr A* to study the physics of stellar mass assembly in an extreme environment as a function of absolute time. I outline the first results from detailed numerical simulations testing this scenario. Finally, I describe a study showing that in terms of the baryonic composition, kinematics, and densities, the gas in the Galactic center is indistinguishable from high-redshift clouds and galaxies. As such, the Galactic center clouds may be used as a template to understand the evolution (and possibly the life cycle) of high-redshift clouds and galaxies.

Star formation across galactic environments

NASA Astrophysics Data System (ADS)

Young, Jason

I present here parallel investigations of star formation in typical and extreme galaxies. The typical galaxies are selected to be free of active galactic nuclei (AGN), while the extreme galaxies host quasars (the most luminous class of AGN). These two environments are each insightful in their own way; quasars are among the most violent objects in the universe, literally reshaping their host galaxies, while my sample of AGN-free star-forming galaxies ranges from systems larger than the Milky Way to small galaxies which are forming stars at unsustainably high rates. The current paradigm of galaxy formation and evolution suggests that extreme circumstances are key stepping stones in the assembly of galaxies like our Milky Way. To test this paradigm and fully explore its ramifications, this dual approach is needed. My sample of AGN-free galaxies is drawn from the KPNO International Spectroscopic Survey. This Halpha-selected, volume-limited survey was designed to detect star-forming galaxies without a bias toward continuum luminosity. This type of selection ensures that this sample is not biased toward galaxies that are large or nearby. My work studies the KISS galaxies in the mid- and far-infrared using photometry from the IRAC and MIPS instruments aboard the Spitzer Space Telescope. These infrared bands are particularly interesting for star formation studies because the ultraviolet light from young stars is reprocessed into thermal emission in the far-infrared (24mum MIPS) by dust and into vibrational transitions features in the mid-infrared (8.0mum IRAC) by polycyclic aromatic hydrocarbons (PAHs). The work I present here examines the efficiencies of PAH and thermal dust emission as tracers of star-formation rates over a wide range of galactic stellar masses. I find that the efficiency of PAH as a star-formation tracer varies with galactic stellar mass, while thermal dust has a highly variable efficiency that does not systematically depend on galactic stellar mass

THE UNREASONABLE WEAKNESS OF R -PROCESS COSMIC RAYS IN THE NEUTRON-STAR-MERGER NUCLEOSYNTHESIS SCENARIO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kyutoku, Koutarou; Ioka, Kunihito, E-mail: koutarou.kyutoku@riken.jp

We reach the robust conclusion that, by combining the observed cosmic rays of r -process elements with the fact that the velocity of the neutron-star-merger ejecta is much higher than that of the supernova ejecta, either (1) the reverse shock in the neutron-star-merger ejecta is a very inefficient accelerator that converts less than 0.003% of the ejecta kinetic energy to the cosmic-ray energy or (2) the neutron star merger is not the origin of the Galactic r -process elements. We also find that the acceleration efficiency should be less than 0.1% for the reverse shock of the supernova ejecta withmore » observed cosmic rays lighter than the iron.« less

Magnetic-distortion-induced Ellipticity and Gravitational Wave Radiation of Neutron Stars: Millisecond Magnetars in Short GRBs, Galactic Pulsars, and Magnetars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, He; Cao, Zhoujian; Zhang, Bing, E-mail: gaohe@bnu.edu.cn

Neutron stars may sustain a non-axisymmetric deformation due to magnetic distortion and are potential sources of continuous gravitational waves (GWs) for ground-based interferometric detectors. With decades of searches using available GW detectors, no evidence of a GW signal from any pulsar has been observed. Progressively stringent upper limits of ellipticity have been placed on Galactic pulsars. In this work, we use the ellipticity inferred from the putative millisecond magnetars in short gamma-ray bursts (SGRBs) to estimate their detectability by current and future GW detectors. For ∼1 ms magnetars inferred from the SGRB data, the detection horizon is ∼30 Mpc andmore » ∼600 Mpc for the advanced LIGO (aLIGO) and Einstein Telescope (ET), respectively. Using the ellipticity of SGRB millisecond magnetars as calibration, we estimate the ellipticity and GW strain of Galactic pulsars and magnetars assuming that the ellipticity is magnetic-distortion-induced. We find that the results are consistent with the null detection results of Galactic pulsars and magnetars with the aLIGO O1. We further predict that the GW signals from these pulsars/magnetars may not be detectable by the currently designed aLIGO detector. The ET detector may be able to detect some relatively low-frequency signals (<50 Hz) from some of these pulsars. Limited by its design sensitivity, the eLISA detector seems to not be suitable for detecting the signals from Galactic pulsars and magnetars.« less

Magnetic-distortion-induced Ellipticity and Gravitational Wave Radiation of Neutron Stars: Millisecond Magnetars in Short GRBs, Galactic Pulsars, and Magnetars

NASA Astrophysics Data System (ADS)

Gao, He; Cao, Zhoujian; Zhang, Bing

2017-08-01

Neutron stars may sustain a non-axisymmetric deformation due to magnetic distortion and are potential sources of continuous gravitational waves (GWs) for ground-based interferometric detectors. With decades of searches using available GW detectors, no evidence of a GW signal from any pulsar has been observed. Progressively stringent upper limits of ellipticity have been placed on Galactic pulsars. In this work, we use the ellipticity inferred from the putative millisecond magnetars in short gamma-ray bursts (SGRBs) to estimate their detectability by current and future GW detectors. For ˜1 ms magnetars inferred from the SGRB data, the detection horizon is ˜30 Mpc and ˜600 Mpc for the advanced LIGO (aLIGO) and Einstein Telescope (ET), respectively. Using the ellipticity of SGRB millisecond magnetars as calibration, we estimate the ellipticity and GW strain of Galactic pulsars and magnetars assuming that the ellipticity is magnetic-distortion-induced. We find that the results are consistent with the null detection results of Galactic pulsars and magnetars with the aLIGO O1. We further predict that the GW signals from these pulsars/magnetars may not be detectable by the currently designed aLIGO detector. The ET detector may be able to detect some relatively low-frequency signals (<50 Hz) from some of these pulsars. Limited by its design sensitivity, the eLISA detector seems to not be suitable for detecting the signals from Galactic pulsars and magnetars.

THE INTERMEDIATE NEUTRON-CAPTURE PROCESS AND CARBON-ENHANCED METAL-POOR STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hampel, Melanie; Stancliffe, Richard J.; Lugaro, Maria

Carbon-enhanced metal-poor (CEMP) stars in the Galactic Halo display enrichments in heavy elements associated with either the s (slow) or the r (rapid) neutron-capture process (e.g., barium and europium, respectively), and in some cases they display evidence of both. The abundance patterns of these CEMP- s / r stars, which show both Ba and Eu enrichment, are particularly puzzling, since the s and the r processes require neutron densities that are more than ten orders of magnitude apart and, hence, are thought to occur in very different stellar sites with very different physical conditions. We investigate whether the abundance patternsmore » of CEMP- s / r stars can arise from the nucleosynthesis of the intermediate neutron-capture process (the i process), which is characterized by neutron densities between those of the s and the r processes. Using nuclear network calculations, we study neutron capture nucleosynthesis at different constant neutron densities n ranging from 10{sup 7}–10{sup 15} cm{sup -3}. With respect to the classical s process resulting from neutron densities on the lowest side of this range, neutron densities on the highest side result in abundance patterns, which show an increased production of heavy s -process and r -process elements, but similar abundances of the light s -process elements. Such high values of n may occur in the thermal pulses of asymptotic giant branch stars due to proton ingestion episodes. Comparison to the surface abundances of 20 CEMP- s / r stars shows that our modeled i -process abundances successfully reproduce observed abundance patterns, which could not be previously explained by s -process nucleosynthesis. Because the i -process models fit the abundances of CEMP- s / r stars so well, we propose that this class should be renamed as CEMP- i .« less

Dibaryons in neutron stars

NASA Technical Reports Server (NTRS)

Olinto, Angela V.; Haensel, Pawel; Frieman, Joshua A.

1991-01-01

The effects are studied of H-dibaryons on the structure of neutron stars. It was found that H particles could be present in neutron stars for a wide range of dibaryon masses. The appearance of dibaryons softens the equations of state, lowers the maximum neutron star mass, and affects the transport properties of dense matter. The parameter space is constrained for dibaryons by requiring that a 1.44 solar mass neutron star be gravitationally stable.

Open star clusters and Galactic structure

NASA Astrophysics Data System (ADS)

Joshi, Yogesh C.

2018-04-01

In order to understand the Galactic structure, we perform a statistical analysis of the distribution of various cluster parameters based on an almost complete sample of Galactic open clusters yet available. The geometrical and physical characteristics of a large number of open clusters given in the MWSC catalogue are used to study the spatial distribution of clusters in the Galaxy and determine the scale height, solar offset, local mass density and distribution of reddening material in the solar neighbourhood. We also explored the mass-radius and mass-age relations in the Galactic open star clusters. We find that the estimated parameters of the Galactic disk are largely influenced by the choice of cluster sample.

The Fate of Merging Neutron Stars

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-08-01

A rapidly spinning, highly magnetized neutron star is one possible outcome when two smaller neutron stars merge. [Casey Reed/Penn State University]When two neutron stars collide, the new object that they make can reveal information about the interior physics of neutron stars. New theoretical work explores what we should be seeing, and what it can teach us.Neutron Star or Black Hole?So far, the only systems from which weve detected gravitational waves are merging black holes. But other compact-object binaries exist and are expected to merge on observable timescales in particular, binary neutron stars. When two neutron stars merge, the resulting object falls into one of three categories:a stable neutron star,a black hole, ora supramassive neutron star, a large neutron star thats supported by its rotation but will eventually collapse to a black hole after it loses angular momentum.Histograms of the initial (left) and final (right) distributions of objects in the authors simulations, for five different equations of state. Most cases resulted primarily in the formation of neutron stars (NSs) or supramassive neutron stars (sNSs), not black holes (BHs). [Piro et al. 2017]Whether a binary-neutron-star merger results in another neutron star, a black hole, or a supramassive neutron star depends on the final mass of the remnant and what the correct equation of state is that describes the interiors of neutron stars a longstanding astrophysical puzzle.In a recent study, a team of scientists led by Anthony Piro (Carnegie Observatories) estimated which of these outcomes we should expect for mergers of binary neutron stars. The teams results along with future observations of binary neutron stars may help us to eventually pin down the equation of state for neutron stars.Merger OutcomesPiro and collaborators used relativistic calculations of spinning and non-spinning neutron stars to estimate the mass range that neutron stars would have for several different realistic equations of

An Upper Bound on Neutron Star Masses from Models of Short Gamma-Ray Bursts

NASA Astrophysics Data System (ADS)

Lawrence, Scott; Tervala, Justin G.; Bedaque, Paulo F.; Miller, M. Coleman

2015-08-01

The discovery of two neutron stars with gravitational masses ≈ 2 {M}⊙ has placed a strong lower limit on the maximum mass of nonrotating neutron stars, and with it a strong constraint on the properties of cold matter beyond nuclear density. Current upper mass limits are much looser. Here, we note that if most short gamma-ray bursts are produced by the coalescence of two neutron stars, and if the merger remnant collapses quickly, then the upper mass limit is constrained tightly. If the rotation of the merger remnant is limited only by mass-shedding (which seems probable based on numerical studies), then the maximum gravitational mass of a nonrotating neutron star is ≈ 2-2.2 {M}⊙ if the masses of neutron stars that coalesce to produce gamma-ray bursts are in the range seen in Galactic double neutron star systems. These limits would be increased by ˜4% in the probably unrealistic case that the remnants rotate at ˜30% below mass-shedding, and by ˜15% in the extreme case that the remnants do not rotate at all. Future coincident detection of short gamma-ray bursts with gravitational waves will strengthen these arguments because they will produce tight bounds on the masses of the components for individual events. If these limits are accurate, then a reasonable fraction of double neutron star mergers might not produce gamma-ray bursts. In that case, or in the case that many short bursts are produced instead by the mergers of neutron stars with black holes, the implied rate of gravitational wave detections will be increased.

The physics of neutron stars.

PubMed

Lattimer, J M; Prakash, M

2004-04-23

Neutron stars are some of the densest manifestations of massive objects in the universe. They are ideal astrophysical laboratories for testing theories of dense matter physics and provide connections among nuclear physics, particle physics, and astrophysics. Neutron stars may exhibit conditions and phenomena not observed elsewhere, such as hyperon-dominated matter, deconfined quark matter, superfluidity and superconductivity with critical temperatures near 10(10) kelvin, opaqueness to neutrinos, and magnetic fields in excess of 10(13) Gauss. Here, we describe the formation, structure, internal composition, and evolution of neutron stars. Observations that include studies of pulsars in binary systems, thermal emission from isolated neutron stars, glitches from pulsars, and quasi-periodic oscillations from accreting neutron stars provide information about neutron star masses, radii, temperatures, ages, and internal compositions.

The Galactic O-Star Spectroscopic Survey (GOSSS): new results from the southern stars

NASA Astrophysics Data System (ADS)

Sota, A.; Maíz Apellániz, J.; Barbá, R. H.; Walborn, N. R.; Alfaro, E. J.; Gamen, R. C.; Morrell, N. I.; Arias, J. I.; Penadés Ordaz, M.

2013-05-01

The Galactic O-Star Spectroscopic Survey (GOSSS) is a project that will observe all known Galactic O stars with B < 14 in the blue-violet part of the spectrum with R ˜ 3000. It is based on v2.0 of the the most complete Galactic O star catalog with accurate spectral types (Maíz Apellániz et al. 2004, ApJS, 151, 103; Sota et al. 2008, RevMexAA Conf. Series, 33, 55) that we have recently compiled. We have completed the first part of the main project and recently published the first articles (Walborn et al. 2010, ApJ, 711, 143; Walborn et al. 2011, AJ, 142, 150; Sota et al. 2011, ApJS, 193, 24). GOSSS is part of a bigger project with the next companion surveys: High resolution spectroscopic surveys: OWN, IACOB, IACOB-sweG, NoMaDS, CAFÉ-BEANS High resolution imaging surveys: Astralux, Astralux Sur.

Trajectories of Cepheid variable stars in the Galactic nuclear bulge

NASA Astrophysics Data System (ADS)

Matsunaga, Noriyuki

2012-06-01

The central region of our Galaxy provides us with a good opportunity to study the evolution of galactic nuclei and bulges because we can observe various phenomena in detail at the proximity of 8 kpc. There is a hierarchical alignment of stellar systems with different sizes; from the extended bulge, the nuclear bulge, down to the compact cluster around the central supermassive blackhole. The nuclear bulge contains stars as young as a few Myr, and even hosts the ongoing star formation. These are in contrast to the more extended bulge which are dominated by old stars, 10Gyr. It is considered that the star formation in the nuclear bulge is caused by fresh gas provided from the inner disk. In this picture, the nuclear bulge plays an important role as the interface between the gas supplier, the inner disk, and the galactic nucleus. Kinematics of young stars in the nuclear bulge is important to discuss the star forming process and the gas circulation in the Galactic Center. We here propose spectroscopic observations of Cepheid variable stars, 25 Myr, which we recently discovered in the nuclear bulge. The spectra taken in this proposal will allow timely estimates of the systemic velocities of the variable stars.

Dusty Mass Loss from Galactic Asymptotic Giant Branch Stars

NASA Astrophysics Data System (ADS)

Sargent, Benjamin A.; Srinivasan, Sundar; Meixner, Margaret; Kastner, Joel H.

2016-06-01

We are probing how mass loss from Asymptotic Giant Branch (AGB) stars depends upon their metallicity. Asymptotic giant branch (AGB) stars are evolved stars that eject large parts of their mass in outflows of dust and gas in the final stages of their lives. Our previous studies focused on mass loss from AGB stars in lower metallicity galaxies: the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). In our present study, we analyze AGB star mass loss in the Galaxy, with special attention to the Bulge, to investigate how mass loss differs in an overall higher metallicity environment. We construct radiative transfer models of the spectral energy distributions (SEDs) of stars in the Galaxy identified as AGB stars from infrared and optical surveys. Our Magellanic Cloud studies found that the AGB stars with the highest mass loss rates tended to have outflows with carbon-rich dust, and that overall more carbon-rich (C-rich) dust than oxygen-rich (O-rich) was produced by AGB stars in both LMC and SMC. Our radiative transfer models have enabled us to determine reliably the dust chemistry of the AGB star from the best-fit model. For our Galactic sample, we are investigating both the dust chemistries of the AGB stars and their mass-loss rates, to compare the balance of C-rich dust to O-rich dust between the Galactic bulge and the Magellanic Clouds. We are also constructing detailed dust opacity models of AGB stars in the Galaxy for which we have infrared spectra; e.g., from the Spitzer Space Telescope Infrared Spectrograph (IRS). This detailed dust modeling of spectra informs our choice of dust properties to use in radiative transfer modeling of SEDs of Galactic AGB stars. BAS acknowledges funding from NASA ADAP grant NNX15AF15G.

r-process enhanched metal-poor stars

NASA Astrophysics Data System (ADS)

Cowan, John; Sneden, Christopher; Lawler, James E.; Den Hartog, Elizabeth A.

Abundance observations indicate the presence of rapid-neutron capture (i.e., r-process) elements in old Galactic halo and globular cluster stars. These observations provide insight into the nature of the earliest generations of stars in the Galaxy - the progenitors of the halo stars - responsible for neutron-capture synthesis of the heavy elements. The large star-to-star scatter observed in the abundances of neutron-capture element/iron ratios at low metallicities - which diminishes with in- creasing metallicity or [Fe/H] - suggests the formation of these heavy elements (presumably from certain types of supernovae) was rare in the early Galaxy. The stellar abundances also indicate a change from the r-process to the slow neutron capture (i.e., s-) process at higher metallicities in the Galaxy and provide insight into Galactic chemical evolution. Finally, the detection of thorium and uranium in halo and globular cluster stars offers an independent age-dating technique that can put lower limits on the age of the Galaxy, and hence the Universe.

Double neutron stars: merger rates revisited

NASA Astrophysics Data System (ADS)

Chruslinska, Martyna; Belczynski, Krzysztof; Klencki, Jakub; Benacquista, Matthew

2018-03-01

We revisit double neutron star (DNS) formation in the classical binary evolution scenario in light of the recent Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo DNS detection (GW170817). The observationally estimated Galactic DNS merger rate of R_MW = 21^{+28}_{-14} Myr-1, based on three Galactic DNS systems, fully supports our standard input physics model with RMW = 24 Myr-1. This estimate for the Galaxy translates in a non-trivial way (due to cosmological evolution of progenitor stars in chemically evolving Universe) into a local (z ≈ 0) DNS merger rate density of Rlocal = 48 Gpc-3 yr-1, which is not consistent with the current LIGO/Virgo DNS merger rate estimate (1540^{+3200}_{-1220} Gpc-3 yr-1). Within our study of the parameter space, we find solutions that allow for DNS merger rates as high as R_local ≈ 600^{+600}_{-300} Gpc-3 yr-1 which are thus consistent with the LIGO/Virgo estimate. However, our corresponding BH-BH merger rates for the models with high DNS merger rates exceed the current LIGO/Virgo estimate of local BH-BH merger rate (12-213 Gpc-3 yr-1). Apart from being particularly sensitive to the common envelope treatment, DNS merger rates are rather robust against variations of several of the key factors probed in our study (e.g. mass transfer, angular momentum loss, and natal kicks). This might suggest that either common envelope development/survival works differently for DNS (˜10-20 M⊙ stars) than for BH-BH (˜40-100 M⊙ stars) progenitors, or high black hole (BH) natal kicks are needed to meet observational constraints for both types of binaries. Our conclusion is based on a limited number of (21) evolutionary models and is valid within this particular DNS and BH-BH isolated binary formation scenario.

Initial data for black hole-neutron star binaries, with rotating stars

NASA Astrophysics Data System (ADS)

Tacik, Nick; Foucart, Francois; Pfeiffer, Harald P.; Muhlberger, Curran; Kidder, Lawrence E.; Scheel, Mark A.; Szilágyi, Béla

2016-11-01

The coalescence of a neutron star with a black hole is a primary science target of ground-based gravitational wave detectors. Constraining or measuring the neutron star spin directly from gravitational wave observations requires knowledge of the dependence of the emission properties of these systems on the neutron star spin. This paper lays foundations for this task, by developing a numerical method to construct initial data for black hole-neutron star binaries with arbitrary spin on the neutron star. We demonstrate the robustness of the code by constructing initial-data sets in large regions of the parameter space. In addition to varying the neutron star spin-magnitude and spin-direction, we also explore neutron star compactness, mass-ratio, black hole spin, and black hole spin-direction. Specifically, we are able to construct initial data sets with neutron stars spinning near centrifugal break-up, and with black hole spins as large as {S}{BH}/{M}{BH}2=0.99.

Probing Neutron Star Evolution with Gamma Rays

NASA Astrophysics Data System (ADS)

Wijers, Ralph A. M. J.

1996-02-01

The research sponsored by this grant was conducted in two fields of high-energy astrophysics: gamma-ray bursts and evolution of neutron stars. It is unknown at this time whether they are related. The work performed in each area is discussed followed by a full list of publications supported by the grant. My research (with E. Fenimore, L. Lubin, B. Paczyiiski, and A. Ulmer) has focussed on devising tests that could distinguish between BATSE and galactic-halo distance scales using the available data. In the first instance, the issue was whether the early BATSE peak flux distribution could be used to extract more than just a slope of the log N(greater than P) distribution, and whether it joined smoothly to the steeper peak flux distribution of bright bursts. To this end, we analysed the peak flux distribution for the presence of a change in slope. This was done both by fitting models with a core radius to see whether a significant value for it could be found, and by developing a completely model-independent test to search for slope changes in arbitrary distributions that are nearly power laws. A slope change was marginally detected in the first-year BATSE data. Good progress has been made in understanding the evolution of neutron stars and their magnetic fields. Having shown in earlier work that magnetic fields in some neutron stars, particularly Her X-1, do not decay spontaneously on million-year time scales, we set out to check whether such spontaneous decay was needed in isolated radio pulsars, as claimed by many. We found that it is not; rather long decay times or no decay are preferred. Since there are neutron stars with low magnetic fields, one must conclude that there is something in their past that distinguishes them from most pulsars. These so-called recycled pulsars are in binaries much more often than normal pulsars. My research concentrates on the class of scenarios in which the recycled pulsars are initially the same as ordinary high-field radio pulsars

Grand unification of neutron stars

PubMed Central

Kaspi, Victoria M.

2010-01-01

The last decade has shown us that the observational properties of neutron stars are remarkably diverse. From magnetars to rotating radio transients, from radio pulsars to isolated neutron stars, from central compact objects to millisecond pulsars, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to establish an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I survey the disparate neutron stars classes, describe their properties, and highlight results made possible by the Chandra X-Ray Observatory, in celebration of its 10th anniversary. Finally, I describe the current status of efforts at physical “grand unification” of this wealth of observational phenomena, and comment on possibilities for Chandra’s next decade in this field. PMID:20404205

Cooling of neutron stars

NASA Technical Reports Server (NTRS)

Pethick, C. J.

1992-01-01

It is at present impossible to predict the interior constitution of neutron stars based on theory and results from laboratory studies. It has been proposed that it is possible to obtain information on neutron star interiors by studying thermal radiation from their surfaces, because neutrino emission rates, and hence the temperature of the central part of a neutron star, depend on the properties of dense matter. The theory predicts that neutron stars cool relatively slowly if their cores are made up of nucleons, and cool faster if the matter is in an exotic state, such as a pion condensate, a kaon condensate, or quark matter. This view has recently been questioned by the discovery of a number of other processes that could lead to copious neutrino emission and rapid cooling.

Constraints on binary neutron star merger product from short GRB observations

NASA Astrophysics Data System (ADS)

Gao, He; Zhang, Bing; Lü, Hou-Jun

2016-02-01

Binary neutron star (NS) mergers are strong gravitational-wave (GW) sources and the leading candidates to interpret short-duration gamma-ray bursts (SGRBs). Under the assumptions that SGRBs are produced by double neutron star mergers and that the x-ray plateau followed by a steep decay as observed in SGRB x-ray light curves marks the collapse of a supramassive neutron star to a black hole (BH), we use the statistical observational properties of Swift SGRBs and the mass distribution of Galactic double neutron star systems to place constraints on the neutron star equation of state (EoS) and the properties of the post-merger product. We show that current observations already impose the following interesting constraints. (1) A neutron star EoS with a maximum mass close to a parametrization of Mmax=2.37 M⊙(1 +1.58 ×10-10P-2.84) is favored. (2) The fractions for the several outcomes of NS-NS mergers are as follows: ˜40 % prompt BHs, ˜30 % supramassive NSs that collapse to BHs in a range of delay time scales, and ˜30 % stable NSs that never collapse. (3) The initial spin of the newly born supramassive NSs should be near the breakup limit (Pi˜1 ms ), which is consistent with the merger scenario. (4) The surface magnetic field of the merger products is typically ˜1015 G . (5) The ellipticity of the supramassive NSs is ɛ ˜(0.004 -0.007 ), so that strong GW radiation is released after the merger. (6) Even though the initial spin energy of the merger product is similar, the final energy output of the merger product that goes into the electromagnetic channel varies in a wide range from several 1049 to several 1052 erg , since a good fraction of the spin energy is either released in the form of GWs or falls into the black hole as the supramassive NS collapses.

Carbon Atmosphere Discovered On Neutron Star

NASA Astrophysics Data System (ADS)

2009-11-01

Evidence for a thin veil of carbon has been found on the neutron star in the Cassiopeia A supernova remnant. This discovery, made with NASA's Chandra X-ray Observatory, resolves a ten-year mystery surrounding this object. "The compact star at the center of this famous supernova remnant has been an enigma since its discovery," said Wynn Ho of the University of Southampton and lead author of a paper that appears in the latest issue of Nature. "Now we finally understand that it can be produced by a hot neutron star with a carbon atmosphere." By analyzing Chandra's X-ray spectrum - akin to a fingerprint of energy - and applying it to theoretical models, Ho and his colleague Craig Heinke, from the University of Alberta, determined that the neutron star in Cassiopeia A, or Cas A for short, has an ultra-thin coating of carbon. This is the first time the composition of an atmosphere of an isolated neutron star has been confirmed. The Chandra "First Light" image of Cas A in 1999 revealed a previously undetected point-like source of X-rays at the center. This object was presumed to be a neutron star, the typical remnant of an exploded star, but researchers were unable to understand its properties. Defying astronomers' expectations, this object did not show any X-ray or radio pulsations or any signs of radio pulsar activity. By applying a model of a neutron star with a carbon atmosphere to this object, Ho and Heinke found that the region emitting X-rays would uniformly cover a typical neutron star. This would explain the lack of X-ray pulsations because -- like a lightbulb that shines consistently in all directions -- this neutron star would be unlikely to display any changes in its intensity as it rotates. Scientists previously have used a neutron star model with a hydrogen atmosphere giving a much smaller emission area, corresponding to a hot spot on a typical neutron star, which should produce X-ray pulsations as it rotates. Interpreting the hydrogen atmosphere model

New Asymptotic Giant Branch Carbon Stars in the Galactic Halo

NASA Astrophysics Data System (ADS)

Mauron, N.; Gigoyan, K. S.; Kostandyan, G. R.

2018-03-01

For the first time the data on the eight confirmed or candidate carbon (C) stars found mainly from objective-prism plates are presented. By using the Catalina database of lightcurves, we find that all these stars are pulsating, allowing a distance to be estimated through the K-band Period-Luminosity (PL) relation. This relation does not depend on spectral type (M or C) and distances are reliable even for C candidates. Seven stars are more than 10 kpc from the galactic plane, suggesting they do not belong to the galactic disk. We also find one star located at about 180 kpc from the Sun, being one of the most distant star in the Galaxy. Many of these new C stars are relatively blue. Some comments are also provided on seven other known halo carbon stars for which either a pulsation period is obtained, or because they were not included in previous works on halo C stars.

Flares from Galactic Centre pulsars: a new class of X-ray transients?

NASA Astrophysics Data System (ADS)

Giannios, Dimitrios; Lorimer, Duncan R.

2016-06-01

Despite intensive searches, the only pulsar within 0.1 pc of the central black hole in our Galaxy, Sgr A*, is a radio-loud magnetar. Since magnetars are rare among the Galactic neutron star population, and a large number of massive stars are already known in this region, the Galactic Centre (GC) should harbour a large number of neutron stars. Population syntheses suggest several thousand neutron stars may be present in the GC. Many of these could be highly energetic millisecond pulsars which are also proposed to be responsible for the GC gamma-ray excess. We propose that the presence of a neutron star within 0.03 pc from Sgr A* can be revealed by the shock interactions with the disc around the central black hole. As we demonstrate, these interactions result in observable transient non-thermal X-ray and gamma-ray emission over time-scales of months, provided that the spin-down luminosity of the neutron star is Lsd ˜ 1035 erg s-1. Current limits on the population of normal and millisecond pulsars in the GC region suggest that a number of such pulsars are present with such luminosities.

Probing the formation history of the nuclear star cluster at the Galactic Centre with millisecond pulsars

NASA Astrophysics Data System (ADS)

Abbate, F.; Mastrobuono-Battisti, A.; Colpi, M.; Possenti, A.; Sippel, A. C.; Dotti, M.

2018-01-01

The origin of the nuclear star cluster in the centre of our Galaxy is still unknown. One possibility is that it formed after the disruption of stellar clusters that spiralled into the Galactic Centre due to dynamical friction. We trace the formation of the nuclear star cluster around the central black hole, using state-of-the-art N-body simulations, and follow the dynamics of the neutron stars born in the clusters. We then estimate the number of millisecond pulsars (MSPs) that are released in the nuclear star cluster during its formation. The assembly and tidal dismemberment of globular clusters lead to a population of MSPs distributed over a radius of about 20 pc, with a peak near 3 pc. No clustering is found on the subparsec scale. We simulate the detectability of this population with future radio telescopes like the MeerKAT radio telescope and SKA1, and find that about an order of 10 MSPs can be observed over this large volume, with a paucity of MSPs within the central parsec. This helps discriminating this scenario from the in situ formation model for the nuclear star cluster that would predict an overabundance of MSPs closer to the black hole. We then discuss the potential contribution of our MSP population to the gamma-ray excess at the Galactic Centre.

ASTE Surveys of Galactic Star-Forming Regions

NASA Astrophysics Data System (ADS)

Kohno, Kotaro

2008-05-01

We report some recent highlights on the observational studies of Galactic star formation based on surveys using the Atacama Submillimeter Telescope Experiment (ASTE), a new 10 m telescope in the Atacama desert in northern Chile (Kohno et al., 2008, ApSS, 313, 279). The highlights will include (1) a large scale CO(3-2) imaging survey of the Galactic Center, unveiling the presence of numerous compact high velocity clouds with high CO(3-2)/CO(1-0) ratios as a "fossil” of the recent burst of star formation in the Galactic Center region (Oka et al., 2007, PASJ, 59, 15; Nagai et al., 2007, PASJ, 59, 25; Tanaka et al., 2007, PASJ, 59, 323), (2) a large scale CO(3-2) imaging survey of the Sgr arm and inter-am regions, revealing the distinct difference on the morphology and physical property of molecular gas between the arm and inter-arm regions for the first time (Sawada, Koda, et al., in prep.), and (3) a wide area 1.1 mm imaging survey of Southern low mass star-forming regions such as Chamaeleon and Lupus molecular clouds using the bolometer camera AzTEC (Wilson et al., 2008, MNRAS, in press) mounted on ASTE, yielding detections of starless cores with a very low mass detection limist down to 0.1 solar masses (Hiramatsu, Tsukagoshi, Kawabe et al., in prep.). Related topics on the massive star-forming regions in very nearby galaxies such as LMC (Minamidani et al., 2008, ApJS, in press) and M 33 (Tosaki et al., 2007, ApJ, 664, L27; Onodera et al., in prep.; Komugi et al., in prep.) will also be reviewed.

Study of a new central compact object: The neutron star in the supernova remnant G15.9+0.2

NASA Astrophysics Data System (ADS)

Klochkov, D.; Suleimanov, V.; Sasaki, M.; Santangelo, A.

2016-08-01

We present our study of the central point source CXOU J181852.0-150213 in the young Galactic supernova remnant (SNR) G15.9+0.2 based on the recent ~90 ks Chandra observations. The point source was discovered in 2005 in shorter Chandra observations and was hypothesized to be a neutron star associated with the SNR. Our X-ray spectral analysis strongly supports the hypothesis of a thermally emitting neutron star associated with G15.9+0.2. We conclude that the object belongs to the class of young cooling low-magnetized neutron stars referred to as central compact objects (CCOs). We modeled the spectrum of the neutron star with a blackbody spectral function and with our hydrogen and carbon neutron star atmosphere models, assuming that the radiation is uniformly emitted by the entire stellar surface. Under this assumption, only the carbon atmosphere models yield a distance that is compatible with a source located in the Galaxy. In this respect, CXOU J181852.0-150213 is similar to two other well-studied CCOs, the neutron stars in Cas A and in HESS J1731-347, for which carbon atmosphere models were used to reconcile their emission with the known or estimated distances.

The galactic reddening law - The evidence from uvby-beta photometry of B stars

NASA Astrophysics Data System (ADS)

Tobin, W.

1985-01-01

Values of interstellar reddening derived from uvby photometry of intermediate and high latitude B stars are used to test between the conflicting ideas of total galactic reddening expounded by Burstein and Heiles (1982) and de Vaucouleurs and Buta (1983). B stars are useful tracers of the galactic reddening because of their empirically and theoretically well-defined colours, and their large distances, but peculiar colours can result in an overestimate of the interstellar reddening, and Nicolet's (1982) B-star estimates of the polar reddening are too high because of this. Selection criteria are developed to exclude B stars with peculiar colours, and 72 selected B stars more than 250 pc from the galactic plane support the Burstein and Heiles zero-point of galactic reddening. The evidence of a few stars supports Burstein and Heiles' use of deep galaxy counts to provide a first-order correction for variations in the dust-to-gas ratio, but for corrections E (b - y) > 0.03 the accuracy may be less than their claimed 10%. However, the comparison of photometrically-derived values of interstellar reddening with values predicted by some model is inevitably partly subjective unless an extensive study is made of every individual star because otherwise any insufficiently red star can always plausibly be discounted as not outside all of the galactic dust, and any star that is too red can always plausibly be discounted as e.g. an undetected binary or emission-line star. The Burstein and Heiles maps are used to determine the intrinsic colours of some slightly-reddened B stars. B stars with projected rotational velocities of 250-300 km s-1 do not appear to be significantly redder than the Crawford (1978) standard relation.

Gravitational Waves from Neutron Stars

NASA Astrophysics Data System (ADS)

Kokkotas, Konstantinos

2016-03-01

Neutron stars are the densest objects in the present Universe, attaining physical conditions of matter that cannot be replicated on Earth. These unique and irreproducible laboratories allow us to study physics in some of its most extreme regimes. More importantly, however, neutron stars allow us to formulate a number of fundamental questions that explore, in an intricate manner, the boundaries of our understanding of physics and of the Universe. The multifaceted nature of neutron stars involves a delicate interplay among astrophysics, gravitational physics, and nuclear physics. The research in the physics and astrophysics of neutron stars is expected to flourish and thrive in the next decade. The imminent direct detection of gravitational waves will turn gravitational physics into an observational science, and will provide us with a unique opportunity to make major breakthroughs in gravitational physics, in particle and high-energy astrophysics. These waves, which represent a basic prediction of Einstein's theory of general relativity but have yet to be detected directly, are produced in copious amounts, for instance, by tight binary neutron star and black hole systems, supernovae explosions, non-axisymmetric or unstable spinning neutron stars. The focus of the talk will be on the neutron star instabilities induced by rotation and the magnetic field. The conditions for the onset of these instabilities and their efficiency in gravitational waves will be presented. Finally, the dependence of the results and their impact on astrophysics and especially nuclear physics will be discussed.

North Galactic Plane Structure with IPHAS Be Stars.

NASA Astrophysics Data System (ADS)

Gkouvelis, L.; Fabregat, J.; IPHAS Consortium

2016-11-01

Our goal is to investigate the spiral structure of the Northern Galactic plane using as tracers the classical Be stars detected by INT Photometric Hα Survey (IPHAS). IPHAS scans the 29ostars, for which we have determined spectral types, astrophysical parameters and distances. From these results we make a first attempt to map the structure of the Galactic disk in the anticenter direction.

The Extinction Toward the Galactic Bulge from RR Lyrae Stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kunder, A; Popowski, P; Cook, K

2007-11-07

The authors present mean reddenings toward 3525 RR0 Lyrae stars from the Galactic bulge fields of the MACHO Survey. These reddenings are determined using the color at minimum V-band light of the RR0 Lyrae stars themselves and are found to be in general agreement with extinction estimates at the same location obtained from other methods. Using 3256 stars located in the Galactic Bulge, they derive the selective extinction coefficient R{sub V,VR} = A{sub V}/E(V-R) = 4.2 {+-} 0.2. this value is what is expected for a standard extinction law with R{sub V,BV} = 3.1 {+-} 0.3

The Impact Of Galactic Environment On Star Formation

NASA Astrophysics Data System (ADS)

Kreckel, Kathryn

2016-09-01

While spiral arms are the most prominent sites for star formation in disk galaxies, interarm star formation contributes significantly to the overall star formation budget. However, it is still an open question if the star formation proceeds differently in the arm and inter-arm environment. We use deep VLT/MUSE optical IFU spectroscopy to resolve and fully characterize the physical properties of 428 interarm and arm HII regions in the nearby grand design spiral galaxy NGC 628. Unlike molecular clouds (the fuel for star formation) which exhibit a clear dependence on galactic environment, we find that most HII region properties (luminosity, size, metallicity, ionization parameter) are independent of environment. One clear exception is the diffuse ionized gas (DIG) contribution to the arm and interarm flux (traced via the temperature sensitive [SII]/Halpha line ratio inside and outside of the HII region boundaries). We find a systematically higher DIG background within HII regions, particularly on the spiral arms. Correcting for this DIG contamination can result in significant (70%) changes to the star formation rate measured. We also show preliminary results comparing well@corrected star formation rates from our MUSE HII regions to ALMA CO(2-1) molecular gas observations at matched 1"=35pc resolution, tracing the Kennicutt-Schmidt star formation law at the scales relevant to the physics of star formation. We estimate the timescales relevant for GMC evolution using distance from the spiral arm as a proxy for age, and test whether star formation feedback or galactic@scale dynamical processes dominate GMC disruption.

The impact of galactic environment on star formation

NASA Astrophysics Data System (ADS)

Kreckel, Kathryn; Blanc, Guillermo A.; Schinnerer, Eva; Groves, Brent; Adamo, Angela; Hughes, Annie; Meidt, Sharon; SFNG Collaboration

2017-01-01

While spiral arms are the most prominent sites for star formation in disk galaxies, interarm star formation contributes significantly to the overall star formation budget. However, it is still an open question if the star formation proceeds differently in the arm and inter-arm environment. We use deep VLT/MUSE optical IFU spectroscopy to resolve and fully characterize the physical properties of 428 interarm and arm HII regions in the nearby grand design spiral galaxy NGC 628. Unlike molecular clouds (the fuel for star formation) which exhibit a clear dependence on galactic environment, we find that most HII region properties (luminosity, size, metallicity, ionization parameter) are independent of environment. One clear exception is the diffuse ionized gas (DIG) contribution to the arm and interarm flux (traced via the temperature sensitive [SII]/Halpha line ratio inside and outside of the HII region boundaries). We find a systematically higher DIG background within HII regions, particularly on the spiral arms. Correcting for this DIG contamination can result in significant (70%) changes to the star formation rate measured. We also show preliminary results comparing well-corrected star formation rates from our MUSE HII regions to ALMA CO(2-1) molecular gas observations at matched 1"=50pc resolution, tracing the Kennicutt-Schmidt star formation law at the scales relevant to the physics of star formation. We estimate the timescales relevant for GMC evolution using distance from the spiral arm as a proxy for age, and test whether star formation feedback or galactic-scale dynamical processes dominate GMC disruption.

Spatial distribution of Galactic Wolf-Rayet stars and implications for the global population

NASA Astrophysics Data System (ADS)

Rosslowe, C. K.; Crowther, P. A.

2015-03-01

We construct revised near-infrared absolute magnitude calibrations for 126 Galactic Wolf-Rayet (WR) stars at known distances, based in part upon recent large-scale spectroscopic surveys. Application to 246 WR stars located in the field permits us to map their Galactic distribution. As anticipated, WR stars generally lie in the thin disc (˜40 pc half-width at half-maximum) between Galactocentric radii 3.5-10 kpc, in accordance with other star formation tracers. We highlight 12 WR stars located at vertical distances of ≥300 pc from the mid-plane. Analysis of the radial variation in WR subtypes exposes a ubiquitously higher NWC/NWN ratio than predicted by stellar evolutionary models accounting for stellar rotation. Models for non-rotating stars or accounting for close binary evolution are more consistent with observations. We consolidate information acquired about the known WR content of the Milky Way to build a simple model of the complete population. We derive observable quantities over a range of wavelengths, allowing us to estimate a total number of 1900 ± 250 Galactic WR stars, implying an average duration of ˜ 0.4 Myr for the WR phase at the current Milky Way star formation rate. Of relevance to future spectroscopic surveys, we use this model WR population to predict follow-up spectroscopy to KS ≃ 17.5 mag will be necessary to identify 95 per cent of Galactic WR stars. We anticipate that ESA's Gaia mission will make few additional WR star discoveries via low-resolution spectroscopy, though will significantly refine existing distance determinations. Appendix A provides a complete inventory of 322 Galactic WR stars discovered since the VIIth catalogue (313 including Annex), including a revised nomenclature scheme.

QPO Constraints on Neutron Stars

NASA Technical Reports Server (NTRS)

Miller, M. Coleman

2005-01-01

The kilohertz frequencies of QPOs from accreting neutron star systems imply that they are generated in regions of strong gravity, close to the star. This suggests that observations of the QPOs can be used to constrain the properties of neutron stars themselves, and in particular to inform us about the properties of cold matter beyond nuclear densities. Here we discuss some relatively model-insensitive constraints that emerge from the kilohertz QPOs, as well as recent developments that may hint at phenomena related to unstable circular orbits outside neutron stars.

Explosive nucleosynthesis in SN 1987A. II - Composition, radioactivities, and the neutron star mass

NASA Technical Reports Server (NTRS)

Thielemann, Friedrich-Karl; Hashimoto, Masa-Aki; Nomoto, Ken'ichi

1990-01-01

The 20 solar mass model of Nomoto and Hashimoto (1988) is utilized with a 6 solar mass. He core is used to perform explosive nucleosynthesis calculations. The employed explosion energy of 10 to the 51st ergs lies within the uncertainty range inferred from the bolometric light curve. The nucleosynthesis processes and their burning products are discussed in detail. The results are compared with abundances from IR observations of SN 1987A and the average nucleosynthesis expected for Type II supernovae in Galactic chemical evolution. The abundances of long-lived radioactive nuclei and their importance for the late light curve and gamma-ray observations are predicted. The position of the mass cut between the neutron star and the ejecta is deduced from the total amount of ejected Ni-56. This requires a neutron star with a baryonic mass of 1.6 + or - 0.045 solar mass, which corresponds to a gravitational mass of 1.43 + or - 0.05 solar mass after subtracting the binding energy of a nonrotating neutron star.

Gravitational Redshift of Deformed Neutron Stars

NASA Astrophysics Data System (ADS)

Romero, Alexis; Zubairi, Omair; Weber, Fridolin

2015-04-01

Non-rotating neutron stars are generally treated in theoretical studies as perfect spheres. Such a treatment, however, may not be correct if strong magnetic fields are present and/or the pressure of the matter in the cores of neutron stars is non-isotropic, leading to neutron stars which are deformed. In this work, we investigate the impact of deformation on the gravitational redshift of neutron stars in the framework of general relativity. Using a parameterized metric to model non-spherical mass distributions, we derive an expression for the gravitational redshift in terms of the mass, radius, and deformity of a neutron star. Numerical solutions for the redshifts of sequences of deformed neutron stars are presented and observational implications are pointed out. This research is funded by the NIH through the Maximizing Access to Research Careers (MARC), under Grant Number: 5T34GM008303-25 and through the National Science Foundation under grant PHY-1411708.

Thermal Evolution of Neutron Stars

NASA Astrophysics Data System (ADS)

Geppert, Ulrich R. M. E.

The thermal evolution of neutron stars is a subject of intense research, both theoretical and observational. The evolution depends very sensitively on the state of dense matter at supranuclear densities, which essentially controls the neutrino emission. The evolution depends, too, on the structure of the stellar outer layers which control the photon emission. Various internal heating processes and the magnetic field strength and structure will influence the thermal evolution. Of great importance for the cooling processes is also whether, when, and where superfluidity and superconductivity appear within the neutron star. This article describes and discusses these issues and presents neutron star cooling calculations based on a broad collection of equations of state for neutron star matter and internal magnetic field geometries. X-ray observations provide reliable data, which allow conclusions about the surface temperatures of neutron stars. To verify the thermal evolution models, the results of model calculations are compared with the body of observed surface temperatures and their distribution. Through these comparisons, a better understanding can be obtained of the physical processes that take place under extreme conditions in the interior of neutron

Jets from Merging Neutron Stars

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-06-01

With the recent discovery of gravitational waves from the merger of two black holes, its especially important to understand the electromagnetic signals resulting from mergers of compact objects. New simulations successfully follow a merger of two neutron stars that produces a short burst of energy via a jet consistent with short gamma-ray burst (sGRB) detections.Still from the authors simulation showing the two neutron stars, and their magnetic fields, before merger. [Adapted from Ruiz et al. 2016]Challenging SystemWe have long suspected that sGRBs are produced by the mergers of compact objects, but this model has been difficult to prove. One major hitch is that modeling the process of merger and sGRB launch is very difficult, due to the fact that these extreme systems involve magnetic fields, fluids and full general relativity.Traditionally, simulations are only able to track such mergers over short periods of time. But in a recent study, Milton Ruiz (University of Illinois at Urbana-Champaign and Industrial University of Santander, Colombia) and coauthors Ryan Lang, Vasileios Paschalidis and Stuart Shapiro have modeled a binary neutron star system all the way through the process of inspiral, merger, and the launch of a jet.A Merger TimelineHow does this happen? Lets walk through one of the teams simulations, in which dipole magnetic field lines thread through the interior of each neutron star and extend beyond its surface(like magnetic fields found in pulsars). In this example, the two neutron stars each have a mass of 1.625 solar masses.Simulation start (0 ms)Loss of energy via gravitational waves cause the neutron stars to inspiral.Merger (3.5 ms)The neutron stars are stretched by tidal effects and make contact. Their merger produces a hypermassive neutron star that is supported against collapse by its differential (nonuniform) rotation.Delayed collapse into a black hole (21.5 ms)Once the differential rotation is redistributed by magnetic fields and partially

Where a Neutron Star's Accretion Disk Ends

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-03-01

In X-ray binaries that consist of a neutron star and a companion star, gas funnels from the companion into an accretion disk surrounding the neutron star, spiraling around until it is eventually accreted. How do the powerful magnetic fields threading through the neutron star affect this accretion disk? Recent observations provide evidence that they may push the accretion disk away from the neutron stars surface.Truncated DisksTheoretical models have indicated that neutron star accretion disks may not extend all the way in to the surface of a neutron star, but may instead be truncated at a distance. This prediction has been difficult to test observationally, however, due to the challenge of measuring the location of the inner disk edge in neutron-star X-ray binaries.In a new study, however, a team of scientists led by Ashley King (Einstein Fellow at Stanford University) has managed to measure the location of the inner edge of the disk in Aquila X-1, a neutron-star X-ray binary located 17,000 light-years away.Iron line feature detected by Swift (red) and NuSTAR (black). The symmetry of the line is one of the indicators that the disk is located far from the neutron star; if the inner regions of the disk were close to the neutron star, severe relativistic effects would skew the line to be asymmetric. [King et al. 2016]Measurements from ReflectionsKing and collaborators used observations made by NuSTAR and Swift/XRT both X-ray space observatories of Aquila X-1 during the peak of an X-ray outburst. By observing the reflection of Aquila X-1s emission off of the inner regions of the accretion disk, the authors were able to estimate the location of the inner edge of the disk.The authors find that this inner edge sits at ~15 gravitational radii. Since the neutron stars surface is at ~5 gravitational radii, this means that the accretion disk is truncated far from the stars surface. In spite of this truncation, material still manages to cross the gap and accrete onto the

Relativistic neutrons in active galactic nuclei

NASA Technical Reports Server (NTRS)

Sikora, Marek; Begelman, Mitchell C.; Rudak, Bronislaw

1989-01-01

The acceleration of protons to relativistic energies in active galactic nuclei leads to the creation of relativistic neutrons which escape from the central engine. The neutrons decay at distances of up to 1-100 pc, depositing their energies and momenta in situ. Energy deposition by decaying neutrons may inhibit spherical accretion and drive a wind, which could be responsible for the velocity fields in emission-line regions and the outflow of broad absorption line systems. Enhanced pressure in the neutron decay region may also help to confine emission line clouds. A fraction of the relativistic proton energy is radiated in gamma-rays with energies which may be as large as about 100,000 GeV.

Mass Loss at Higher Metallicity: Quantifying the Mass Return from Evolved Stars in the Galactic

NASA Astrophysics Data System (ADS)

Sargent, Benjamin

Bulge Mass-losing evolved stars, and in particular asymptotic giant branch (AGB) stars and red supergiant (RSG) stars, are expected to be the major producers of dust in galaxies. This dust will help form planetary systems around future generations of stars. Our ADAP program to measure the mass loss from the AGB and RSG stars in the Magellanic Clouds is nearing completion, and we wish to extend this successful study to the Galactic bulge of the Milky Way Galaxy. Metallicity should determine the amount of elements available to condense dust in the star's outflow, so evolved stars of differing metallicities should have differing mass-loss rates. Building upon our work on evolved stars in the Magellanic Clouds, we will compare the mass-loss rates from AGB and RSG stars in the older and potentially more metal-rich Bulge to the mass-loss rates of AGB and RSG stars in the Magellanic Clouds, which have lower metallicity, making for an interesting contrast. In addition, the Galactic bulge, like the Clouds, is located at a well-determined distance ( 8 kpc), thereby removing the distance ambiguities that present a major uncertainty in determining mass-loss rates and luminosities for evolved stars. To model photometric observations of outflowing dust shells around evolved stars, we have constructed the Grid of Red supergiant and Asymptotic giant branch ModelS (GRAMS; Sargent et al 2011; Srinivasan et al 2011) using the radiative transfer code 2Dust (Ueta and Meixner 2003). Our study will apply these models to the large photometric database of sources identified in the Spitzer Space Telescope GLIMPSE survey of the Milky Way and also to the various infrared spectra of Bulge AGB and RSG stars from Spitzer, ISO, etc. We have already modeled a few Galactic bulge evolved stars with GRAMS, and we will use these results as the foundation for modeling a large and representative sample of Galactic bulge evolved stars identified and measured photometrically by GLIMPSE. We will use our

Neutron star evolution and emission

NASA Astrophysics Data System (ADS)

Epstein, R. I.; Edwards, B. C.; Haines, T. J.

1997-01-01

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The authors investigated the evolution and radiation characteristics of individual neutron stars and stellar systems. The work concentrated on phenomena where new techniques and observations are dramatically enlarging the understanding of stellar phenomena. Part of this project was a study of x-ray and gamma-ray emission from neutron stars and other compact objects. This effort included calculating the thermal x-ray emission from young neutron stars, deriving the radio and gamma-ray emission from active pulsars and modeling intense gamma-ray bursts in distant galaxies. They also measured periodic optical and infrared fluctuations from rotating neutron stars and search for high-energy TeV gamma rays from discrete celestial sources.

Burst Oscillations: Watching Neutron Stars Spin

NASA Technical Reports Server (NTRS)

Strohmayer, Tod

2010-01-01

It is now almost 15 years since the first detection of rotationally modulated emission from X-ray bursting neutron stars, "burst oscillations," This phenomenon enables us to see neutron stars spin, as the X-ray burst flux asymmetrically lights up the surface. It has enabled a new way to probe the neutron star spin frequency distribution, as well as to elucidate the multidimensional nature of nuclear burning on neutron stars. I will review our current observational understanding of the phenomenon, with an eye toward highlighting some of the interesting remaining puzzles, of which there is no shortage.

NUCLEOSYNTHESIS CONSTRAINTS ON THE NEUTRON STAR-BLACK HOLE MERGER RATE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bauswein, A.; Ardevol Pulpillo, R.; Janka, H.-T.

2014-11-01

We derive constraints on the time-averaged event rate of neutron star-black hole (NS-BH) mergers by using estimates of the population-integrated production of heavy rapid neutron-capture (r-process) elements with nuclear mass numbers A > 140 by such events in comparison to the Galactic repository of these chemical species. Our estimates are based on relativistic hydrodynamical simulations convolved with theoretical predictions of the binary population. This allows us to determine a strict upper limit of the average NS-BH merger rate of ∼6× 10{sup –5} per year. We quantify the uncertainties of this estimate to be within factors of a few mostly becausemore » of the unknown BH spin distribution of such systems, the uncertain equation of state of NS matter, and possible errors in the Galactic content of r-process material. Our approach implies a correlation between the merger rates of NS-BH binaries and of double NS systems. Predictions of the detection rate of gravitational-wave signals from such compact object binaries by Advanced LIGO and Advanced Virgo on the optimistic side are incompatible with the constraints set by our analysis.« less

Origin of Neutron Stars

NASA Astrophysics Data System (ADS)

Brecher, K.

1999-12-01

The origin of the concept of neutron stars can be traced to two brief, incredibly insightful publications. Work on the earlier paper by Lev Landau (Phys. Z. Sowjetunion, 1, 285, 1932) actually predated the discovery of neutrons. Nonetheless, Landau arrived at the notion of a collapsed star with the density of a nucleus (really a "nucleus star") and demonstrated (at about the same time as, and independent of, Chandrasekhar) that there is an upper mass limit for dense stellar objects of about 1.5 solar masses. Perhaps even more remarkable is the abstract of a talk presented at the December 1933 meeting of the American Physical Society published by Walter Baade and Fritz Zwicky in 1934 (Phys. Rev. 45, 138). It followed the discovery of the neutron by just over a year. Their report, which was about the same length as the present abstract: (1) invented the concept and word supernova; (2) suggested that cosmic rays are produced by supernovae; and (3) in the authors own words, proposed "with all reserve ... the view that supernovae represent the transitions from ordinary stars to neutron stars (italics), which in their final stages consist of extremely closely packed neutrons." The abstract by Baade and Zwicky probably contains the highest density of new, important (and correct) ideas in high energy astrophysics ever published in a single paper. In this talk, we will discuss some of the facts and myths surrounding these two publications.

Cooling of Accretion-Heated Neutron Stars

NASA Astrophysics Data System (ADS)

Wijnands, Rudy; Degenaar, Nathalie; Page, Dany

2017-09-01

We present a brief, observational review about the study of the cooling behaviour of accretion-heated neutron stars and the inferences about the neutron-star crust and core that have been obtained from these studies. Accretion of matter during outbursts can heat the crust out of thermal equilibrium with the core and after the accretion episodes are over, the crust will cool down until crust-core equilibrium is restored. We discuss the observed properties of the crust cooling sources and what has been learned about the physics of neutron-star crusts. We also briefly discuss those systems that have been observed long after their outbursts were over, i.e, during times when the crust and core are expected to be in thermal equilibrium. The surface temperature is then a direct probe for the core temperature. By comparing the expected temperatures based on estimates of the accretion history of the targets with the observed ones, the physics of neutron-star cores can be investigated. Finally, we discuss similar studies performed for strongly magnetized neutron stars in which the magnetic field might play an important role in the heating and cooling of the neutron stars.

NuSTAR results from the Galactic Center - diffuse emission

NASA Astrophysics Data System (ADS)

Hailey, Charles

2016-03-01

The Nuclear Spectroscopic Telescope Array (NuSTAR) was launched in June 2012. It carried the first true, hard X-ray (>~10 keV-79 keV) focusing telescopes into orbit. Its twin telescopes provide 10 times better angular resolution and 100 times better sensitivity than previously obtainable in the hard X-ray band. Consequently NuSTAR is able to resolve faint diffuse structures whose hard X-rays offer insight into some of the most energetic processes in the Galactic Center. One of the surprising discoveries that NuSTAR made in the Galactic Center is the central hard X-ray emission (CHXE). The CHXE is a diffuse emission detected from ~10 keV to beyond 50 keV in X-ray energy, and extending spatially over a region ~8 parsecs x ~4 parsecs in and out of the plane of the galaxy respectively, and centered on the supermassive black hole Sgr A*. The CHXE was speculated to be due to a large population of unresolved black hole X-ray binaries, millisecond pulsars (MSP), a class of highly magnetized white dwarf binaries called intermediate polars, or to particle outflows from Sgr A*. The presence of an unexpectedly large population of MSP in the Galactic Center would be particularly interesting, since MSP emitting at higher energies and over a much larger region have been posited to be the origin of the gamma-ray emission that is also ascribed to dark matter annihilation in the galaxy. In addition, the connection of the CHXE to the ~9000 unidentified X-ray sources in the central the the ~100 pc detected by the Chandra Observatory, to the soft X-ray emission detected by the Chandra and XMM/Newton observatories in the Galactic Center, and to the hard X-ray emission detected by both the RXTE and INTEGRAL observatories in the Galactic Ridge, is unclear. I review these results and present recent NuSTAR observations that potentially resolve the origin of the CHXE and point to a unified origin for all these X-ray emissions. Two other noteworthy classes of diffuse structures in the

Neutron stars velocities and magnetic fields

NASA Astrophysics Data System (ADS)

Paret, Daryel Manreza; Martinez, A. Perez; Ayala, Alejandro.; Piccinelli, G.; Sanchez, A.

2018-01-01

We study a model that explain neutron stars velocities due to the anisotropic emission of neutrinos. Strong magnetic fields present in neutron stars are the source of the anisotropy in the system. To compute the velocity of the neutron star we model its core as composed by strange quark matter and analice the properties of a magnetized quark gas at finite temperature and density. Specifically we have obtained the electron polarization and the specific heat of magnetized fermions as a functions of the temperature, chemical potential and magnetic field which allow us to study the velocity of the neutron star as a function of these parameters.

A NEAR-INFRARED SURVEY OF THE INNER GALACTIC PLANE FOR WOLF-RAYET STARS. II. GOING FAINTER: 71 MORE NEW W-R STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shara, Michael M.; Faherty, Jacqueline K.; Zurek, David

We are continuing a J, K and narrowband imaging survey of 300 deg{sup 2} of the plane of the Galaxy, searching for new Wolf-Rayet (W-R) stars. Our survey spans 150 Degree-Sign in Galactic longitude and reaches 1 Degree-Sign above and below the Galactic plane. The survey has a useful limiting magnitude of K = 15 over most of the observed Galactic plane, and K = 14 (due to severe crowding) within a few degrees of the Galactic center. Thousands of emission-line candidates have been detected. In spectrographic follow-ups of 146 relatively bright W-R star candidates, we have re-examined 11 previouslymore » known WC and WN stars and discovered 71 new W-R stars, 17 of type WN and 54 of type WC. Our latest image analysis pipeline now picks out W-R stars with a 57% success rate. Star subtype assignments have been confirmed with the K-band spectra and distances approximated using the method of spectroscopic parallax. Some of the new W-R stars are among the most distant known in our Galaxy. The distribution of these new W-R stars is beginning to trace the locations of massive stars along the distant spiral arms of the Milky Way.« less

Theory of Radiation Transfer in Neutron Star Atmospheres

NASA Technical Reports Server (NTRS)

Zavlin, Vyacheslav

2006-01-01

The possibility for direct investigation of thermal emission from isolated neutron stars opened about a quarter of century ago with the launch of the first X-ray observatories Einstein and EXOSAT stimulated developing models of the neutron star surface radiation which began at the end of 80's. Confronting observational data with theoretical models of thermal emission allows one to infer the surface temperatures, magnetic fields, chemical composition, and neutron star masses and radii. This information, supplemented with the model equations of state and neutron star cooling models, provides an opportunity to understand the fundamental properties of the superdense matter in the stars' interiors. Almost all available models are based on the assumption that thermal radiation emitted by a neutron star is formed in the superficial star's layers--atmosphere. The neutron star atmospheres are very different from those of usual stars due to the immense gravity and huge magnetic fields. In this presentation we review the current status of the neutron star atmosphere modeling, present most important results, discuss problems and possible future developments.

Gravitational waves from neutron stars and asteroseismology.

PubMed

Ho, Wynn C G

2018-05-28

Neutron stars are born in the supernova explosion of massive stars. Neutron stars rotate as stably as atomic clocks and possess densities exceeding that of atomic nuclei and magnetic fields millions to billions of times stronger than those created in laboratories on the Earth. The physical properties of neutron stars are determined by many areas of fundamental physics, and detection of gravitational waves can provide invaluable insights into our understanding of these areas. Here, we describe some of the physics and astrophysics of neutron stars and how traditional electromagnetic wave observations provide clues to the sorts of gravitational waves we expect from these stars. We pay particular attention to neutron star fluid oscillations, examining their impact on electromagnetic and gravitational wave observations when these stars are in a wide binary or isolated system, then during binary inspiral right before merger, and finally at times soon after merger.This article is part of a discussion meeting issue 'The promises of gravitational-wave astronomy'. © 2018 The Author(s).

Gravitational waves from neutron stars and asteroseismology

NASA Astrophysics Data System (ADS)

Ho, Wynn C. G.

2018-05-01

Neutron stars are born in the supernova explosion of massive stars. Neutron stars rotate as stably as atomic clocks and possess densities exceeding that of atomic nuclei and magnetic fields millions to billions of times stronger than those created in laboratories on the Earth. The physical properties of neutron stars are determined by many areas of fundamental physics, and detection of gravitational waves can provide invaluable insights into our understanding of these areas. Here, we describe some of the physics and astrophysics of neutron stars and how traditional electromagnetic wave observations provide clues to the sorts of gravitational waves we expect from these stars. We pay particular attention to neutron star fluid oscillations, examining their impact on electromagnetic and gravitational wave observations when these stars are in a wide binary or isolated system, then during binary inspiral right before merger, and finally at times soon after merger. This article is part of a discussion meeting issue `The promises of gravitational-wave astronomy'.

Stellar Structure Models of Deformed Neutron Stars

NASA Astrophysics Data System (ADS)

Zubairi, Omair; Wigley, David; Weber, Fridolin

Traditional stellar structure models of non-rotating neutron stars work under the assumption that these stars are perfect spheres. This assumption of perfect spherical symmetry is not correct if the matter inside neutron stars is described by an anisotropic model for the equation of state. Certain classes of neutron stars such as Magnetars and neutron stars which contain color-superconducting quark matter cores are expected to be deformed making them oblong spheroids. In this work, we investigate the stellar structure of these deformed neutron stars by deriving stellar structure equations in the framework of general relativity. Using a non-isotropic equation of state model, we solve these structure equations numerically in two dimensions. We calculate stellar properties such as masses and radii along with pressure profiles and investigate changes from standard spherical models.

Nuclear Physics of neutron stars

NASA Astrophysics Data System (ADS)

Piekarewicz, Jorge

2015-04-01

One of the overarching questions posed by the recent community report entitled ``Nuclear Physics: Exploring the Heart of Matter'' asks How Does Subatomic Matter Organize Itself and What Phenomena Emerge? With their enormous dynamic range in both density and neutron-proton asymmetry, neutron stars provide ideal laboratories to answer this critical challenge. Indeed, a neutron star is a gold mine for the study of physical phenomena that cut across a variety of disciplines, from particle physics to general relativity. In this presentation--targeted at non-experts--I will focus on the essential role that nuclear physics plays in constraining the dynamics, structure, and composition of neutron stars. In particular, I will discuss some of the many exotic states of matter that are speculated to exist in a neutron star and the impact of nuclear-physics experiments on elucidating their fascinating nature. This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Nuclear Physics under Award Number DE-FD05-92ER40750.

Journey to the Center of a Neutron Star

NASA Technical Reports Server (NTRS)

Wanjek, Christopher

2003-01-01

A neutron star is not a place most would want to visit. This dense remnant of a collapsed star has a magnetic field billions of times stronger than Earth's, enough to shuffle your body's molecules long before you even land. The featureless surface is no fun either. Crushing gravity ensures that the star is a near perfect sphere, compressing all matter so that a sand-grain-sized scoop of neutron star material would weigh as much as a battleship on Earth. At least black holes offer the promise of funky singularity, time warps, and the Odyssean temptation to venture beyond a point of no return. What s a journey to a neutron star good for, one might ask? Well, for starters, it offers the possibility of confirming a theorized state of matter called quark-gluon plasma, which likely existed for a moment after the Big Bang and now might only exist in the superdense interiors of neutron stars. Beneath the neutron star crust, a kilometer-thick plate of crystalline matter, lies the great unknown. The popular theory is that the neutron star interior is made up of a neutron superfluid - a fluid without friction. With the help of two NASA satellites - the Rossi X-Ray Timing Explorer and the Chandra X-Ray Observatory - scientists are journeying to the center of a neutron star. Matter might be so compressed there that it breaks down into quarks, the building blocks of protons and neutrons, and gluons, the carrier of the strong nuclear force. To dig inside a neutron star, no simple drill bit will do. Scientists gain insight into the interior through events called glitches, a sudden change in the neutron star s precise spin rate. 'Glitches are one of the few ways we have to study the neutron star interior,' says Frank Marshall of NASA s Goddard Space Flight Center, who has used the Rossi Explorer to follow the escapades of the glitchiest of all neutron stars, dubbed the Big Glitcher and known scientifically as PSR J0537-6910.

A weight limit emerges for neutron stars

NASA Astrophysics Data System (ADS)

Cho, Adrian

2018-02-01

Astrophysicists have long wondered how massive a neutron star—the corpse of certain exploding stars—could be without collapsing under its own gravity to form a black hole. Now, four teams have independently deduced a mass limit for neutron stars of about 2.2 times the mass of the sun. To do so, all four groups analyzed last year's blockbuster observations of the merger of two neutron stars, spied on 17 September 2017 by dozens of observatories. That approach may seem unpromising, as it might appear that the merging neutron stars would have immediately produced a black hole. However, the researchers argue that the merger first produced a spinning, overweight neutron star momentarily propped up by centrifugal force. They deduce that just before it collapsed, the short-lived neutron star had to be near the maximum mass for one spinning as a solid body. That inference allowed them to use a scaling relationship to estimate the maximum mass of a nonrotating, stable neutron star, starting from the total mass of the original pair and the amount of matter spewed into space.

Superfluidity in the Core of Neutron Stars

NASA Astrophysics Data System (ADS)

Page, Dany

2013-04-01

The year (1958) after the publication of the BCS theory, Bohr, Mottelson & Pines showed that nuclei should also contain superfluid neutrons and superconducting protons. In 1959, A. Migdal proposed that neutron superfluidity should also occur in the interior of neutron stars. Pairing in nuclei forms Cooper pairs with zero spin, but the relevant component of the nuclear interaction becomes repulsive at densities larger than the nuclear matter density. It has been proposed that neutron-neutron interaction in the spin-triplet state, and L=1 orbital angular momentum, that is known to be attractive from laboratory experiments, may result in a new form of neutron superfluidity in the neutron star interior. I will review our present understanding of the structure of neutron stars and describe how superfluidity strongly affects their thermal evolution. I will show how a ``Minimal Model'' that excludes the presence of ``exotic'' matter (Bose condensates, quarks, etc.) is compatible with most observations of the surface temperatures of young isolated neutron stars in the case this neutron superfluid exists. Compared to the case of isotropic spin-zero Cooper pairs, the formation of anisotropic spin-one Cooper pairs results in a strong neutrino emission that leads to an enhanced cooling of neutron stars after the onset of the pairing phase transition and allows the Minimal Cooling scenario to be compatible with most observations. In the case the pairing critical temperature Tc is less than about 6 x10^8 K, the resulting rapid cooling of the neutron star may be observable. It was recently reported that 10 years of Chandra observations of the 333 year young neutron star in the Cassiopeia A supernova remnant revealed that its temperature has dropped by about 5%. This result indicates that neutrons in this star are presently becoming superfluid and, if confirmed, provides us with the first direct observational evidence for neutron superfluidity at supra-nuclear densities.

I-Love-Q: unexpected universal relations for neutron stars and quark stars.

PubMed

Yagi, Kent; Yunes, Nicolás

2013-07-26

Neutron stars and quark stars are not only characterized by their mass and radius but also by how fast they spin, through their moment of inertia, and how much they can be deformed, through their Love number and quadrupole moment. These depend sensitively on the star's internal structure and thus on unknown nuclear physics. We find universal relations between the moment of inertia, the Love number, and the quadrupole moment that are independent of the neutron and quark star's internal structure. These can be used to learn about neutron star deformability through observations of the moment of inertia, break degeneracies in gravitational wave detection to measure spin in binary inspirals, distinguish neutron stars from quark stars, and test general relativity in a nuclear structure-independent fashion.

Lithium and zirconium abundances in massive Galactic O-rich AGB stars

NASA Astrophysics Data System (ADS)

García-Hernández, D. A.; García-Lario, P.; Plez, B.; Manchado, A.; D'Antona, F.; Lub, J.; Habing, H.

2007-02-01

Lithium and zirconium abundances (the latter taken as representative of s-process enrichment) are determined for a large sample of massive Galactic O-rich AGB stars, for which high-resolution optical spectroscopy has been obtained (R˜ 40 000{-}50 000). This was done by computing synthetic spectra based on classical hydrostatic model atmospheres for cool stars and using extensive line lists. The results are discussed in the framework of "hot bottom burning" (HBB) and nucleosynthesis models. The complete sample is studied for various observational properties such as the position of the stars in the IRAS two-colour diagram ([ 12] - [25] vs. [ 25] - [60] ), Galactic distribution, expansion velocity (derived from the OH maser emission), and period of variability (when available). We conclude that a considerable fraction of these sources are actually massive AGB stars (M>3{-}4 M⊙) experiencing HBB, as deduced from the strong Li overabundances we found. A comparison of our results with similar studies carried out in the past for the Magellanic Clouds (MCs) reveals that, in contrast to MC AGB stars, our Galactic sample does not show any indication of s-process element enrichment. The differences observed are explained as a consequence of metallicity effects. Finally, we discuss the results obtained in the framework of stellar evolution by comparing our results with the data available in the literature for Galactic post-AGB stars and PNe. Based on observations at the 4.2 m William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofisica de Canarias. Also based on observations with the ESO 3.6 m telescope at La Silla Observatory (Chile). Tables [see full text]-[see full text] are only available in electronic form at http://www.aanda.org

Testing Intermittence of the Galactic Star Formation History along with the Infall Model

NASA Astrophysics Data System (ADS)

Takeuchi, Tsutomu T.; Hirashita, Hiroyuki

2000-09-01

We analyze the star formation history (SFH) of the Galactic disk by using an infall model. Based on the observed SFH of the Galactic disk, we first determine the timescale of the gas infall into the Galactic disk (tin) and that of the gas consumption to form stars (tsf). Since each of the two timescales does not prove to be determined independently from the SFH, we first fix tsf. Then, tin is determined so that we minimize χ2. Consequently, we choose three parameter sets: [tsf (Gyr),tin (Gyr)]=(6.0, 23), (11, 12), and (15, 9.0), where we set the Galactic age as 15 Gyr. All of the three cases predict almost identical star formation history. Next, we test the intermittence (or variability) of the star formation rate (SFR) along with the smooth SFH suggested from the infall model. The large value of the χ2 statistic supports the violent time variation of the SFH. If we interpret the observed SFH with smooth and variable components, the amplitude of the variable component is comparable to the smooth component. Thus, intermittent SFH of the Galactic disk is strongly suggested. We also examined the metallicity distribution of G dwarfs. We found that the true parameter set lies between [tsf (Gyr),tin (Gyr)]=(6, 23) and (11, 12), though we need a more sophisticated model including the process of metal enrichment within the Galactic halo.

Gravitational waves from remnant massive neutron stars of binary neutron star merger: Viscous hydrodynamics effects

NASA Astrophysics Data System (ADS)

Shibata, Masaru; Kiuchi, Kenta

2017-06-01

Employing a simplified version of the Israel-Stewart formalism of general-relativistic shear-viscous hydrodynamics, we explore the evolution of a remnant massive neutron star of binary neutron star merger and pay special attention to the resulting gravitational waveforms. We find that for the plausible values of the so-called viscous alpha parameter of the order 10-2 the degree of the differential rotation in the remnant massive neutron star is significantly reduced in the viscous time scale, ≲5 ms . Associated with this, the degree of nonaxisymmetric deformation is also reduced quickly, and as a consequence, the amplitude of quasiperiodic gravitational waves emitted also decays in the viscous time scale. Our results indicate that for modeling the evolution of the merger remnants of binary neutron stars we would have to take into account magnetohydrodynamics effects, which in nature could provide the viscous effects.

Binary neutron stars with arbitrary spins in numerical relativity

NASA Astrophysics Data System (ADS)

Tacik, Nick; Foucart, Francois; Pfeiffer, Harald P.; Haas, Roland; Ossokine, Serguei; Kaplan, Jeff; Muhlberger, Curran; Duez, Matt D.; Kidder, Lawrence E.; Scheel, Mark A.; Szilágyi, Béla

2015-12-01

We present a code to construct initial data for binary neutron star systems in which the stars are rotating. Our code, based on a formalism developed by Tichy, allows for arbitrary rotation axes of the neutron stars and is able to achieve rotation rates near rotational breakup. We compute the neutron star angular momentum through quasilocal angular momentum integrals. When constructing irrotational binary neutron stars, we find a very small residual dimensionless spin of ˜2 ×10-4 . Evolutions of rotating neutron star binaries show that the magnitude of the stars' angular momentum is conserved, and that the spin and orbit precession of the stars is well described by post-Newtonian approximation. We demonstrate that orbital eccentricity of the binary neutron stars can be controlled to ˜0.1 % . The neutron stars show quasinormal mode oscillations at an amplitude which increases with the rotation rate of the stars.

Limiting rotational period of neutron stars

NASA Astrophysics Data System (ADS)

Glendenning, Norman K.

1992-11-01

We seek an absolute limit on the rotational period for a neutron star as a function of its mass, based on the minimal constraints imposed by Einstein's theory of relativity, Le Chatelier's principle, causality, and a low-density equation of state, uncertainties in which can be evaluated as to their effect on the result. This establishes a limiting curve in the mass-period plane below which no pulsar that is a neutron star can lie. For example, the minimum possible Kepler period, which is an absolute limit on rotation below which mass shedding would occur, is 0.33 ms for a M=1.442Msolar neutron star (the mass of PSR1913+16). A still lower curve, based only on the structure of Einstein's equations, limits any star whatsoever to lie in the plane above it. Hypothetical stars such as strange stars, if the matter of which they are made is self-bound in bulk at a sufficiently large equilibrium energy density, can lie in the region above the general-relativistic forbidden region, and in the region forbidden to neutron stars.

Cracking on anisotropic neutron stars

NASA Astrophysics Data System (ADS)

Setiawan, A. M.; Sulaksono, A.

2017-07-01

We study the effect of cracking of a local anisotropic neutron star (NS) due to small density fluctuations. It is assumed that the neutron star core consists of leptons, nucleons and hyperons. The relativistic mean field model is used to describe the core of equation of state (EOS). For the crust, we use the EOS introduced by Miyatsu et al. [1]. Furthermore, two models are used to describe pressure anisotropic in neutron star matter. One is proposed by Doneva-Yazadjiev (DY) [2] and the other is proposed by Herrera-Barreto (HB) [3]. The anisotropic parameter of DY and HB models are adjusted in order the predicted maximum mass compatible to the mass of PSR J1614-2230 [4] and PSR J0348+0432 [5]. We have found that cracking can potentially present in the region close to the neutron star surface. The instability due cracking is quite sensitive to the NS mass and anisotropic parameter used.

Hot stars in young massive clusters: Mapping the current Galactic metallicity

NASA Astrophysics Data System (ADS)

de la Fuente, Diego; Najarro, Francisco; Davies, Ben; Trombley, Christine; Figer, Donald F.; Herrero, Artemio

2013-06-01

Young Massive Clusters (YMCs) with ages < 6 Myr are ideal tools for mapping the current chemical abundances in the Galactic disk for several reasons. First of all, the locations of these clusters can be known through spectrophotometric distances. Secondly, their young ages guarantee that these objects present the same chemical composition than the surrounding environment where they are recently born. Finally, the YMCs host very massive stars whose extreme luminosities allow to accomplish detailed spectroscopic analyses even in the most distant regions of the Milky Way. Our group has carried out ISAAC/VLT spectroscopic observations of hot massive stars belonging to several YMCs in different locations around the Galactic disk. As a result, high signal-to-noise, near-infrared spectra of dozens of blue massive stars (including many OB supergiants, Wolf-Rayet stars and a B hypergiant) have been obtained. These data are fully reduced, and NLTE spherical atmosphere modeling is in process. Several line diagnostics will be combined in order to calculate metal abundances accurately for each cluster. The diverse locations of the clusters will allow us to draw a two-dimensional chemical map of the Galactic disk for the first time. The study of the radial and azimuthal variations of elemental abundances will be crucial for understanding the chemical evolution of the Milky Way. Particularly, the ratio between Fe-peak and alpha elements will constitute a powerful tool to investigate the past stellar populations that originated the current Galactic chemistry.

Unveiling the Role of Galactic Rotation on Star Formation

NASA Astrophysics Data System (ADS)

Utreras, José; Becerra, Fernando; Escala, Andrés

2016-12-01

We study the star formation process at galactic scales and the role of rotation through numerical simulations of spiral and starburst galaxies using the adaptive mesh refinement code Enzo. We focus on the study of three integrated star formation laws found in the literature: the Kennicutt-Schmidt (KS) and Silk-Elmegreen (SE) laws, and the dimensionally homogeneous equation proposed by Escala {{{Σ }}}{SFR}\\propto \\sqrt{G/L}{{{Σ }}}{gas}1.5. We show that using the last we take into account the effects of the integration along the line of sight and find a unique regime of star formation for both types of galaxies, suppressing the observed bi-modality of the KS law. We find that the efficiencies displayed by our simulations are anti-correlated with the angular velocity of the disk Ω for the three laws studied in this work. Finally, we show that the dimensionless efficiency of star formation is well represented by an exponentially decreasing function of -1.9{{Ω }}{t}{ff}{ini}, where {t}{ff}{ini} is the initial free-fall time. This leads to a unique galactic star formation relation which reduces the scatter of the bi-modal KS, SE, and Escala relations by 43%, 43%, and 35%, respectively.

The Origin of IRS 16: Dynamically Driven In-Spiral of a Dense Star Cluster to the Galactic Center?

NASA Astrophysics Data System (ADS)

Portegies Zwart, Simon F.; McMillan, Stephen L. W.; Gerhard, Ortwin

2003-08-01

We use direct N-body simulations to study the in-spiral and internal evolution of dense star clusters near the Galactic center. These clusters sink toward the center owing to dynamical friction with the stellar background and may go into core collapse before being disrupted by the Galactic tidal field. If a cluster reaches core collapse before disruption, its dense core, which has become rich in massive stars, survives to reach close to the Galactic center. When it eventually dissolves, the cluster deposits a disproportionate number of massive stars in the innermost parsec of the Galactic nucleus. Comparing the spatial distribution and kinematics of the massive stars with observations of IRS 16, a group of young He I stars near the Galactic center, we argue that this association may have formed in this way.

The Galactic interstellar medium: foregrounds and star formation

NASA Astrophysics Data System (ADS)

Miville-Deschênes, Marc-Antoine

2018-05-01

This review presents briefly two aspects of Galactic interstellar medium science that seem relevant for studying EoR. First, we give some statistical properties of the Galactic foreground emission in the diffuse regions of the sky. The properties of the emission observed in projection on the plane of the sky are then related to how matter is organised along the line of sight. The diffuse atomic gas is multi-phase, with dense filamentary structures occupying only about 1% of the volume but contributing to about 50% of the emission. The second part of the review presents aspect of structure formation in the Galactic interstellar medium that could be relevant for the subgrid physics used to model the formation of the first stars.

Lightweight Double Neutron Star Found

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-02-01

More than forty years after the first discovery of a double neutron star, we still havent found many others but a new survey is working to change that.The Hunt for PairsThe observed shift in the Hulse-Taylor binarys orbital period over time as it loses energy to gravitational-wave emission. [Weisberg Taylor, 2004]In 1974, Russell Hulse and Joseph Taylor discovered the first double neutron star: two compact objects locked in a close orbit about each other. Hulse and Taylors measurements of this binarys decaying orbit over subsequent years led to a Nobel prize and the first clear evidence of gravitational waves carrying energy and angular momentum away from massive binaries.Forty years later, we have since confirmed the existence of gravitational waves directly with the Laser Interferometer Gravitational-Wave Observatory (LIGO). Nonetheless, finding and studying pre-merger neutron-star binaries remains a top priority. Observing such systems before they merge reveals crucial information about late-stage stellar evolution, binary interactions, and the types of gravitational-wave signals we expect to find with current and future observatories.Since the Hulse-Taylor binary, weve found a total of 16 additional double neutron-star systems which represents only a tiny fraction of the more than 2,600 pulsars currently known. Recently, however, a large number of pulsar surveys are turning their eyes toward the sky, with a focus on finding more double neutron stars and at least one of them has had success.The pulse profile for PSR J1411+2551 at 327 MHz. [Martinez et al. 2017]A Low-Mass DoubleConducted with the 1,000-foot Arecibo radio telescope in Puerto Rico, the Arecibo 327 MHz Drift Pulsar Survey has enabled the recent discovery of dozens of pulsars and transients. Among them, as reported by Jose Martinez (Max Planck Institute for Radio Astronomy) and coauthors in a recent publication, is PSR J1411+2551: a new double neutron star with one of the lowest masses ever measured

Binary Neutron Stars with Arbitrary Spins in Numerical Relativity

NASA Astrophysics Data System (ADS)

Pfeiffer, Harald; Tacik, Nick; Foucart, Francois; Haas, Roland; Kaplan, Jeffrey; Muhlberger, Curran; Duez, Matt; Kidder, Lawrence; Scheel, Mark; Szilagyi, Bela

2015-04-01

We present a code to construct initial data for binary neutron star where the stars are rotating. Our code, based on the formalism developed by Tichy, allows for arbitrary rotation axes of the neutron stars and is able to achieve rotation rates near rotational breakup. We demonstrate that orbital eccentricity of the binary neutron stars can be controlled to ~ 0 . 1 % . Preliminary evolutions show that spin- and orbit-precession of Neutron stars is well described by post-Newtonian approximation. The neutron stars show quasi-normal mode oscillations at an amplitude which increases with the rotation rate of the stars.

The Outcome of Neutron Star Mergers

NASA Astrophysics Data System (ADS)

Foucart, Francois

2014-10-01

Black hole-neutron star and neutron star-neutron star mergers are among the main sources of gravitational waves which will be detected in the coming years by the Advanced LIGO/VIRGO/KAGRA observatories. In some cases, these mergers can also power bright electromagnetic emissions: they are the most likely progenitors of short gamma-ray bursts, and the radioactive decay of neutron-rich material ejected by the merger can power optical/infrared transients days after the merger. Finally, they may provide important constraints on the equation of state of cold dense matter, and on the source of heavy elements in the universe. I will discuss the general relativistic simulations which are required to properly model these events, and what they have told us so far about the outcome of neutron star mergers. I will also discuss efforts to improve the physical realism of the simulations by improving the treatment of the most important effects beyond general relativistic hydrodynamics: magnetic fields, neutrinos, and the properties of nuclear matter.

Finding evolved stars in the inner Galactic disk with Gaia

NASA Astrophysics Data System (ADS)

Quiroga-Nuñez, L. H.; van Langevelde, H. J.; Pihlström, Y. M.; Sjouwerman, L. O.; Brown, A. G. A.

2018-04-01

The Bulge Asymmetries and Dynamical Evolution (BAaDE) survey will provide positions and line-of-sight velocities of ~20, 000 evolved, maser bearing stars in the Galactic plane. Although this Galactic region is affected by optical extinction, BAaDE targets may have Gaia cross-matches, eventually providing additional stellar information. In an initial attempt to cross-match BAaDE targets with Gaia, we have found more than 5,000 candidates. Of these, we may expect half to show SiO emission, which will allow us to obtain velocity information. The cross-match is being refined to avoid false positives using different criteria based on distance analysis, flux variability, and color assessment in the mid- and near-IR. Once the cross-matches can be confirmed, we will have a unique sample to characterize the stellar population of evolved stars in the Galactic bulge, which can be considered fossils of the Milky Way formation.

Star-disc interaction in galactic nuclei: orbits and rates of accreted stars

NASA Astrophysics Data System (ADS)

Kennedy, Gareth F.; Meiron, Yohai; Shukirgaliyev, Bekdaulet; Panamarev, Taras; Berczik, Peter; Just, Andreas; Spurzem, Rainer

2016-07-01

We examine the effect of an accretion disc on the orbits of stars in the central star cluster surrounding a central massive black hole by performing a suite of 39 high-accuracy direct N-body simulations using state-of-the art software and accelerator hardware, with particle numbers up to 128k. The primary focus is on the accretion rate of stars by the black hole (equivalent to their tidal disruption rate for black holes in the small to medium mass range) and the eccentricity distribution of these stars. Our simulations vary not only the particle number, but disc model (two models examined), spatial resolution at the centre (characterized by the numerical accretion radius) and softening length. The large parameter range and physically realistic modelling allow us for the first time to confidently extrapolate these results to real galactic centres. While in a real galactic centre both particle number and accretion radius differ by a few orders of magnitude from our models, which are constrained by numerical capability, we find that the stellar accretion rate converges for models with N ≥ 32k. The eccentricity distribution of accreted stars, however, does not converge. We find that there are two competing effects at work when improving the resolution: larger particle number leads to a smaller fraction of stars accreted on nearly circular orbits, while higher spatial resolution increases this fraction. We scale our simulations to some nearby galaxies and find that the expected boost in stellar accretion (or tidal disruption, which could be observed as X-ray flares) in the presence of a gas disc is about a factor of 10. Even with this boost, the accretion of mass from stars is still a factor of ˜100 slower than the accretion of gas from the disc. Thus, it seems accretion of stars is not a major contributor to black hole mass growth.

Color excesses, intrinsic colors, and absolute magnitudes of Galactic and Large Magellanic Cloud Wolf-Rayet stars

NASA Technical Reports Server (NTRS)

Vacca, William D.; Torres-Dodgen, Ana V.

1990-01-01

A new method of determining the color excesses of WR stars in the Galaxy and the LMC has been developed and is used to determine the excesses for 44 Galactic and 32 LMC WR stars. The excesses are combined with line-free, narrow-band spectrophotometry to derive intrinsic colors of the WR stars of nearly all spectral subtypes. No correlation of UV spectral index or intrinsic colors with spectral subtype is found for the samples of single WN or WC stars. There is evidence that early WN stars in the LMC have flatter UV continua and redder intrinsic colors than early WN stars in the Galaxy. No separation is found between the values derived for Galactic WC stars and those obtained for LMC WC stars. The intrinsic colors are compared with those calculated from model atmospheres of WR stars and generally good agreement is found. Absolute magnitudes are derived for WR stars in the LMC and for those Galactic WR stars located in clusters and associations for which there are reliable distance estimates.

Magnetic neutron star cooling and microphysics

NASA Astrophysics Data System (ADS)

Potekhin, A. Y.; Chabrier, G.

2018-01-01

Aims: We study the relative importance of several recent updates of microphysics input to the neutron star cooling theory and the effects brought about by superstrong magnetic fields of magnetars, including the effects of the Landau quantization in their crusts. Methods: We use a finite-difference code for simulation of neutron-star thermal evolution on timescales from hours to megayears with an updated microphysics input. The consideration of short timescales (≲1 yr) is made possible by a treatment of the heat-blanketing envelope without the quasistationary approximation inherent to its treatment in traditional neutron-star cooling codes. For the strongly magnetized neutron stars, we take into account the effects of Landau quantization on thermodynamic functions and thermal conductivities. We simulate cooling of ordinary neutron stars and magnetars with non-accreted and accreted crusts and compare the results with observations. Results: Suppression of radiative and conductive opacities in strongly quantizing magnetic fields and formation of a condensed radiating surface substantially enhance the photon luminosity at early ages, making the life of magnetars brighter but shorter. These effects together with the effect of strong proton superfluidity, which slows down the cooling of kiloyear-aged neutron stars, can explain thermal luminosities of about a half of magnetars without invoking heating mechanisms. Observed thermal luminosities of other magnetars are still higher than theoretical predictions, which implies heating, but the effects of quantizing magnetic fields and baryon superfluidity help to reduce the discrepancy.

Neutron stars: Observational diversity and evolution

NASA Astrophysics Data System (ADS)

Safi-Harb, S.

2017-12-01

Ever since the discovery of the Crab and Vela pulsars in their respective Supernova Remnants, our understanding of how neutron stars manifest themselves observationally has been dramatically shaped by the surge of discoveries and dedicated studies across the electromagnetic spectrum, particularly in the high-energy band. The growing diversity of neutron stars includes the highly magnetized neutron stars (magnetars) and the Central Compact Objects shining in X-rays and mostly lacking pulsar wind nebulae. These two subclasses of high-energy objects, however, seem to be characterized by anomalously high or anomalously low surface magnetic fields (thus dubbed as ‘magnetars’ and ‘anti-magnetars’, respectively), and have pulsar characteristic ages that are often much offset from their associated SNRs’ ages. In addition, some neutron stars act ‘schizophrenic’ in that they occasionally display properties that seem common to more than one of the defined subclasses. I review the growing diversity of neutron stars from an observational perspective, then highlight recent and on-going theoretical and observational work attempting to address this diversity, particularly in light of their magnetic field evolution, energy loss mechanisms, and supernova progenitors’ studies.

Tidal breakup of triple stars in the Galactic Centre

NASA Astrophysics Data System (ADS)

Fragione, Giacomo; Gualandris, Alessia

2018-04-01

The last decade has seen the detection of fast moving stars in the Galactic halo, the so-called hypervelocity stars (HVSs). While the bulk of this population is likely the result of a close encounter between a stellar binary and the supermassive black hole (MBH) in the Galactic Centre (GC), other mechanims may contribute fast stars to the sample. Few observed HVSs show apparent ages, which are shorter than the flight time from the GC, thereby making the binary disruption scenario unlikely. These stars may be the result of the breakup of a stellar triple in the GC, which led to the ejection of a hypervelocity binary (HVB). If such binary evolves into a blue straggler star due to internal processes after ejection, a rejuvenation is possible that make the star appear younger once detected in the halo. A triple disruption may also be responsible for the presence of HVBs, of which one candidate has now been observed. We present a numerical study of triple disruptions by the MBH in the GC and find that the most likely outcomes are the production of single HVSs and single/binary stars bound to the MBH, while the production of HVBs has a probability ≲ 1 per cent regardless of the initial parameters. Assuming a triple fraction of ≈ 10 per cent results in an ejection rate of ≲ 1 Gyr - 1, insufficient to explain the sample of HVSs with lifetimes shorter than their flight time. We conclude that alternative mechanisms are responsible for the origin of such objects and HVBs in general.

Resolving Star Formation, Multiphase ISM Structure, and Wind Driving with MHD and RHD Models of Galactic Disks

NASA Astrophysics Data System (ADS)

Ostriker, Eve

Current studies of star and galaxy formation have concluded that energetic feedback from young stars and supernovae (SNe) is crucial, both for controlling observed interstellar medium (ISM) properties and star formation rates in the Milky Way and other galaxies, and for driving galactic winds that govern the baryon abundance in dark matter halos. However, in many numerical studies of the ISM, energy inputs have not been implemented self-consistently with the evolving rate of gravitational collapse to make stars, or have considered only isolated star-forming clouds without a realistic galactic environment (including sheared rotation and externally-originating SNe), or have not directly incorporated radiation, magnetic, and chemical effects that are important or even dominant. In models of galaxy formation and evolution in the cosmic context, galactic winds are indispensable but highly uncertain as the physics of superbubble evolution and radiation-gas interactions cannot be resolved. Our central objectives are (1) to address the above limitations of current models, developing self-consistent simulations of the multiphase ISM in disk galaxies that resolve both star formation and stellar feedback, covering the range of scales needed to connect star cluster formation to galactic superwind ejection, and the range of environments from dwarfs to ULIRGs; and (2) to analyze the detailed properties of the gas, magnetic field, radiation field, and star formation/SNe in our simulations, including dependencies on local galactic disk environment, and to connect intrinsic properties with observable diagnostics. The proposed project will employ the Athena code for numerical magneto-hydrodynamic (MHD) and radiation-hydrodynamic (RHD) simulations, using comprehensive physics modules that have been developed, tested, and demonstrated in sample simulations. We will consider local ``shearing box'' disk models with gas surface density Sigma = 2 - 10,000 Msun/pc^2, and a range of stellar

NASA'S Chandra Finds Superfluid in Neutron Star's Core

NASA Astrophysics Data System (ADS)

2011-02-01

NASA's Chandra X-ray Observatory has discovered the first direct evidence for a superfluid, a bizarre, friction-free state of matter, at the core of a neutron star. Superfluids created in laboratories on Earth exhibit remarkable properties, such as the ability to climb upward and escape airtight containers. The finding has important implications for understanding nuclear interactions in matter at the highest known densities. Neutron stars contain the densest known matter that is directly observable. One teaspoon of neutron star material weighs six billion tons. The pressure in the star's core is so high that most of the charged particles, electrons and protons, merge resulting in a star composed mostly of uncharged particles called neutrons. Two independent research teams studied the supernova remnant Cassiopeia A, or Cas A for short, the remains of a massive star 11,000 light years away that would have appeared to explode about 330 years ago as observed from Earth. Chandra data found a rapid decline in the temperature of the ultra-dense neutron star that remained after the supernova, showing that it had cooled by about four percent over a 10-year period. "This drop in temperature, although it sounds small, was really dramatic and surprising to see," said Dany Page of the National Autonomous University in Mexico, leader of a team with a paper published in the February 25, 2011 issue of the journal Physical Review Letters. "This means that something unusual is happening within this neutron star." Superfluids containing charged particles are also superconductors, meaning they act as perfect electrical conductors and never lose energy. The new results strongly suggest that the remaining protons in the star's core are in a superfluid state and, because they carry a charge, also form a superconductor. "The rapid cooling in Cas A's neutron star, seen with Chandra, is the first direct evidence that the cores of these neutron stars are, in fact, made of superfluid and

Neutron Skins and Neutron Stars in the Multimessenger Era

NASA Astrophysics Data System (ADS)

Fattoyev, F. J.; Piekarewicz, J.; Horowitz, C. J.

2018-04-01

The historical first detection of a binary neutron star merger by the LIGO-Virgo Collaboration [B. P. Abbott et al., Phys. Rev. Lett. 119, 161101 (2017), 10.1103/PhysRevLett.119.161101] is providing fundamental new insights into the astrophysical site for the r process and on the nature of dense matter. A set of realistic models of the equation of state (EOS) that yield an accurate description of the properties of finite nuclei, support neutron stars of two solar masses, and provide a Lorentz covariant extrapolation to dense matter are used to confront its predictions against tidal polarizabilities extracted from the gravitational-wave data. Given the sensitivity of the gravitational-wave signal to the underlying EOS, limits on the tidal polarizability inferred from the observation translate into constraints on the neutron-star radius. Based on these constraints, models that predict a stiff symmetry energy, and thus large stellar radii, can be ruled out. Indeed, we deduce an upper limit on the radius of a 1.4 M⊙ neutron star of R⋆1.4<13.76 km . Given the sensitivity of the neutron-skin thickness of Pb 208 to the symmetry energy, albeit at a lower density, we infer a corresponding upper limit of about Rskin208≲0.25 fm . However, if the upcoming PREX-II experiment measures a significantly thicker skin, this may be evidence of a softening of the symmetry energy at high densities—likely indicative of a phase transition in the interior of neutron stars.

Neutron stars in supernova remnants and beyond

NASA Astrophysics Data System (ADS)

Gvaramadze, V.

We propose a new approach for studying the neutron star/supernova remnant associations, based on the idea that the supernova remnants can be products of an off-centered supernova explosion in a preexisting bubble created by the wind of a moving massive star. A cavity supernova explosion of a moving star results in a considerable offset of the neutron star birth-place from the geometrical center of the supernova remnant. Therefore: a) the high transverse velocities inferred for a number of neutron stars through their association with supernova remnants can be reduced; b) the proper motion vector of a neutron star should not necessarily point away from the geometrical center of the associated supernova remnant. Taking into account these two facts allow us to enlarge the circle of possible neutron star/supernova remnant associations, and could significantly affect the results of previous studies of associations. The possibilities of our approach are illustrated with some examples. We also show that the concept of an off-centered cavity supernova explosion could be used to explain the peculiar structures of a number of supernova remnants and for searches for stellar remnants possibly associated with them.

Upper Limits on the Rates of Binary Neutron Star and Neutron Star-Black Hole Mergers from Advanced LIGO’s First Observing Run

NASA Astrophysics Data System (ADS)

Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M. R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X.; Adya, V. B.; Affeldt, C.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O. D.; Aiello, L.; Ain, A.; Ajith, P.; Allen, B.; Allocca, A.; Altin, P. A.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Araya, M. C.; Arceneaux, C. C.; Areeda, J. S.; Arnaud, N.; Arun, K. G.; Ascenzi, S.; Ashton, G.; Ast, M.; Aston, S. M.; Astone, P.; Aufmuth, P.; Aulbert, C.; Babak, S.; Bacon, P.; Bader, M. K. M.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Barayoga, J. C.; Barclay, S. E.; Barish, B. C.; Barker, D.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barta, D.; Bartlett, J.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Baune, C.; Bavigadda, V.; Bazzan, M.; Bejger, M.; Bell, A. S.; Berger, B. K.; Bergmann, G.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Birch, J.; Birney, R.; Biscans, S.; Bisht, A.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blair, C. D.; Blair, D. G.; Blair, R. M.; Bloemen, S.; Bock, O.; Boer, M.; Bogaert, G.; Bogan, C.; Bohe, A.; Bond, C.; Bondu, F.; Bonnand, R.; Boom, B. A.; Bork, R.; Boschi, V.; Bose, S.; Bouffanais, Y.; Bozzi, A.; Bradaschia, C.; Brady, P. R.; Braginsky, V. B.; Branchesi, M.; Brau, J. E.; Briant, T.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brockill, P.; Broida, J. E.; Brooks, A. F.; Brown, D. A.; Brown, D. D.; Brown, N. M.; Brunett, S.; Buchanan, C. C.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cabero, M.; Cadonati, L.; Cagnoli, G.; Cahillane, C.; Calderón Bustillo, J.; Callister, T.; Calloni, E.; Camp, J. B.; Cannon, K. C.; Cao, J.; Capano, C. D.; Capocasa, E.; Carbognani, F.; Caride, S.; Casanueva Diaz, J.; Casentini, C.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C. B.; Cerboni Baiardi, L.; Cerretani, G.; Cesarini, E.; Chamberlin, S. J.; Chan, M.; Chao, S.; Charlton, P.; Chassande-Mottin, E.; Cheeseboro, B. D.; Chen, H. Y.; Chen, Y.; Cheng, C.; Chincarini, A.; Chiummo, A.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Q.; Chua, S.; Chung, S.; Ciani, G.; Clara, F.; Clark, J. A.; Cleva, F.; Coccia, E.; Cohadon, P.-F.; Colla, A.; Collette, C. G.; Cominsky, L.; Constancio., M., Jr.; Conte, A.; Conti, L.; Cook, D.; Corbitt, T. R.; Cornish, N.; Corsi, A.; Cortese, S.; Costa, C. A.; Coughlin, M. W.; Coughlin, S. B.; Coulon, J.-P.; Countryman, S. T.; Couvares, P.; Cowan, E. E.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Craig, K.; Creighton, J. D. E.; Cripe, J.; Crowder, S. G.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dal Canton, T.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Darman, N. S.; Dasgupta, A.; Da Silva Costa, C. F.; Dattilo, V.; Dave, I.; Davier, M.; Davies, G. S.; Daw, E. J.; Day, R.; De, S.; DeBra, D.; Debreczeni, G.; Degallaix, J.; De Laurentis, M.; Deléglise, S.; Del Pozzo, W.; Denker, T.; Dent, T.; Dergachev, V.; De Rosa, R.; DeRosa, R. T.; DeSalvo, R.; Devine, R. C.; Dhurandhar, S.; Díaz, M. C.; Di Fiore, L.; Di Giovanni, M.; Di Girolamo, T.; Di Lieto, A.; Di Pace, S.; Di Palma, I.; Di Virgilio, A.; Dolique, V.; Donovan, F.; Dooley, K. L.; Doravari, S.; Douglas, R.; Downes, T. P.; Drago, M.; Drever, R. W. P.; Driggers, J. C.; Ducrot, M.; Dwyer, S. E.; Edo, T. B.; Edwards, M. C.; Effler, A.; Eggenstein, H.-B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Engels, W.; Essick, R. C.; Etzel, T.; Evans, M.; Evans, T. M.; Everett, R.; Factourovich, M.; Fafone, V.; Fair, H.; Fairhurst, S.; Fan, X.; Fang, Q.; Farinon, S.; Farr, B.; Farr, W. M.; Favata, M.; Fays, M.; Fehrmann, H.; Fejer, M. M.; Fenyvesi, E.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Fiori, I.; Fiorucci, D.; Fisher, R. P.; Flaminio, R.; Fletcher, M.; Fournier, J.-D.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Frey, V.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Gabbard, H. A. G.; Gair, J. R.; Gammaitoni, L.; Gaonkar, S. G.; Garufi, F.; Gaur, G.; Gehrels, N.; Gemme, G.; Geng, P.; Genin, E.; Gennai, A.; George, J.; Gergely, L.; Germain, V.; Ghosh, Abhirup; Ghosh, Archisman; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gill, K.; Glaefke, A.; Goetz, E.; Goetz, R.; Gondan, L.; González, G.; Gonzalez Castro, J. M.; Gopakumar, A.; Gordon, N. A.; Gorodetsky, M. L.; Gossan, S. E.; Gosselin, M.; Gouaty, R.; Grado, A.; Graef, C.; Graff, P. B.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Green, A. C.; Groot, P.; Grote, H.; Grunewald, S.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Hacker, J. J.; Hall, B. R.; Hall, E. D.; Hammond, G.; Haney, M.; Hanke, M. M.; Hanks, J.; Hanna, C.; Hannam, M. D.; Hanson, J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M. J.; Hartman, M. T.; Haster, C.-J.; Haughian, K.; Heidmann, A.; Heintze, M. C.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Hennig, J.; Henry, J.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hoak, D.; Hofman, D.; Holt, K.; Holz, D. E.; Hopkins, P.; Hough, J.; Houston, E. A.; Howell, E. J.; Hu, Y. M.; Huang, S.; Huerta, E. A.; Huet, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh-Dinh, T.; Indik, N.; Ingram, D. R.; Inta, R.; Isa, H. N.; Isac, J.-M.; Isi, M.; Isogai, T.; Iyer, B. R.; Izumi, K.; Jacqmin, T.; Jang, H.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jian, L.; Jiménez-Forteza, F.; Johnson, W. W.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; K, Haris; Kalaghatgi, C. V.; Kalogera, V.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Kapadia, S. J.; Karki, S.; Karvinen, K. S.; Kasprzack, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kaur, T.; Kawabe, K.; Kéfélian, F.; Kehl, M. S.; Keitel, D.; Kelley, D. B.; Kells, W.; Kennedy, R.; Key, J. S.; Khalili, F. Y.; Khan, I.; Khan, S.; Khan, Z.; Khazanov, E. A.; Kijbunchoo, N.; Kim, Chi-Woong; Kim, Chunglee; Kim, J.; Kim, K.; Kim, N.; Kim, W.; Kim, Y.-M.; Kimbrell, S. J.; King, E. J.; King, P. J.; Kissel, J. S.; Klein, B.; Kleybolte, L.; Klimenko, S.; Koehlenbeck, S. M.; Koley, S.; Kondrashov, V.; Kontos, A.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Kringel, V.; Krishnan, B.; Królak, A.; Krueger, C.; Kuehn, G.; Kumar, P.; Kumar, R.; Kuo, L.; Kutynia, A.; Lackey, B. D.; Landry, M.; Lange, J.; Lantz, B.; Lasky, P. D.; Laxen, M.; Lazzarini, A.; Lazzaro, C.; Leaci, P.; Leavey, S.; Lebigot, E. O.; Lee, C. H.; Lee, H. K.; Lee, H. M.; Lee, K.; Lenon, A.; Leonardi, M.; Leong, J. R.; Leroy, N.; Letendre, N.; Levin, Y.; Lewis, J. B.; Li, T. G. F.; Libson, A.; Littenberg, T. B.; Lockerbie, N. A.; Lombardi, A. L.; London, L. T.; Lord, J. E.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J. D.; Lück, H.; Lundgren, A. P.; Lynch, R.; Ma, Y.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magaña-Sandoval, F.; Magaña Zertuche, L.; Magee, R. M.; Majorana, E.; Maksimovic, I.; Malvezzi, V.; Man, N.; Mandic, V.; Mangano, V.; Mansell, G. L.; Manske, M.; Mantovani, M.; Marchesoni, F.; Marion, F.; Márka, S.; Márka, Z.; Markosyan, A. S.; Maros, E.; Martelli, F.; Martellini, L.; Martin, I. W.; Martynov, D. V.; Marx, J. N.; Mason, K.; Masserot, A.; Massinger, T. J.; Masso-Reid, M.; Mastrogiovanni, S.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McGuire, S. C.; McIntyre, G.; McIver, J.; McManus, D. J.; McRae, T.; McWilliams, S. T.; Meacher, D.; Meadors, G. D.; Meidam, J.; Melatos, A.; Mendell, G.; Mercer, R. A.; Merilh, E. L.; Merzougui, M.; Meshkov, S.; Messenger, C.; Messick, C.; Metzdorff, R.; Meyers, P. M.; Mezzani, F.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, A. L.; Miller, A.; Miller, B. B.; Miller, J.; Millhouse, M.; Minenkov, Y.; Ming, J.; Mirshekari, S.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moggi, A.; Mohan, M.; Mohapatra, S. R. P.; Montani, M.; Moore, B. C.; Moore, C. J.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mossavi, K.; Mours, B.; Mow-Lowry, C. M.; Mueller, G.; Muir, A. W.; Mukherjee, Arunava; Mukherjee, D.; Mukherjee, S.; Mukund, N.; Mullavey, A.; Munch, J.; Murphy, D. J.; Murray, P. G.; Mytidis, A.; Nardecchia, I.; Naticchioni, L.; Nayak, R. K.; Nedkova, K.; Nelemans, G.; Nelson, T. J. N.; Neri, M.; Neunzert, A.; Newton, G.; Nguyen, T. T.; Nielsen, A. B.; Nissanke, S.; Nitz, A.; Nocera, F.; Nolting, D.; Normandin, M. E. N.; Nuttall, L. K.; Oberling, J.; Ochsner, E.; O'Dell, J.; Oelker, E.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Oliver, M.; Oppermann, P.; Oram, Richard J.; O'Reilly, B.; O'Shaughnessy, R.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pai, A.; Pai, S. A.; Palamos, J. R.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, H.; Pankow, C.; Pannarale, F.; Pant, B. C.; Paoletti, F.; Paoli, A.; Papa, M. A.; Paris, H. R.; Parker, W.; Pascucci, D.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Patricelli, B.; Patrick, Z.; Pearlstone, B. L.; Pedraza, M.; Pedurand, R.; Pekowsky, L.; Pele, A.; Penn, S.; Perreca, A.; Perri, L. M.; Phelps, M.; Piccinni, O. J.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pitkin, M.; Poe, M.; Poggiani, R.; Popolizio, P.; Post, A.; Powell, J.; Prasad, J.; Predoi, V.; Prestegard, T.; Price, L. R.; Prijatelj, M.; Principe, M.; Privitera, S.; Prix, R.; Prodi, G. A.; Prokhorov, L.; Puncken, O.; Punturo, M.; Puppo, P.; Pürrer, M.; Qi, H.; Qin, J.; Qiu, S.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Raab, F. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raja, S.; Rajan, C.; Rakhmanov, M.; Rapagnani, P.; Raymond, V.; Razzano, M.; Re, V.; Read, J.; Reed, C. M.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Rew, H.; Reyes, S. D.; Ricci, F.; Riles, K.; Rizzo, M.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V. J.; Romano, R.; Romanov, G.; Romie, J. H.; Rosińska, D.; Rowan, S.; Rüdiger, A.; Ruggi, P.; Ryan, K.; Sachdev, S.; Sadecki, T.; Sadeghian, L.; Sakellariadou, M.; Salconi, L.; Saleem, M.; Salemi, F.; Samajdar, A.; Sammut, L.; Sanchez, E. J.; Sandberg, V.; Sandeen, B.; Sanders, J. R.; Sassolas, B.; Sathyaprakash, B. S.; Saulson, P. R.; Sauter, O. E. S.; Savage, R. L.; Sawadsky, A.; Schale, P.; Schilling, R.; Schmidt, J.; Schmidt, P.; Schnabel, R.; Schofield, R. M. S.; Schönbeck, A.; Schreiber, E.; Schuette, D.; Schutz, B. F.; Scott, J.; Scott, S. M.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sequino, V.; Sergeev, A.; Setyawati, Y.; Shaddock, D. A.; Shaffer, T.; Shahriar, M. S.; Shaltev, M.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Shoemaker, D. M.; Siellez, K.; Siemens, X.; Sieniawska, M.; Sigg, D.; Silva, A. D.; Singer, A.; Singer, L. P.; Singh, A.; Singh, R.; Singhal, A.; Sintes, A. M.; Slagmolen, B. J. J.; Smith, J. R.; Smith, N. D.; Smith, R. J. E.; Son, E. J.; Sorazu, B.; Sorrentino, F.; Souradeep, T.; Srivastava, A. K.; Staley, A.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stephens, B. C.; Stone, R.; Strain, K. A.; Straniero, N.; Stratta, G.; Strauss, N. A.; Strigin, S.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sunil, S.; Sutton, P. J.; Swinkels, B. L.; Szczepańczyk, M. J.; Tacca, M.; Talukder, D.; Tanner, D. B.; Tápai, M.; Tarabrin, S. P.; Taracchini, A.; Taylor, R.; Theeg, T.; Thirugnanasambandam, M. P.; Thomas, E. G.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thrane, E.; Tiwari, S.; Tiwari, V.; Tokmakov, K. V.; Toland, K.; Tomlinson, C.; Tonelli, M.; Tornasi, Z.; Torres, C. V.; Torrie, C. I.; Töyrä, D.; Travasso, F.; Traylor, G.; Trifirò, D.; Tringali, M. C.; Trozzo, L.; Tse, M.; Turconi, M.; Tuyenbayev, D.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Valdes, G.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; Van Den Broeck, C.; Vander-Hyde, D. C.; van der Schaaf, L.; van Heijningen, J. V.; van Veggel, A. A.; Vardaro, M.; Vass, S.; Vasúth, M.; Vaulin, R.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Verkindt, D.; Vetrano, F.; Viceré, A.; Vinciguerra, S.; Vine, D. J.; Vinet, J.-Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Voss, D. V.; Vousden, W. D.; Vyatchanin, S. P.; Wade, A. R.; Wade, L. E.; Wade, M.; Walker, M.; Wallace, L.; Walsh, S.; Wang, G.; Wang, H.; Wang, M.; Wang, X.; Wang, Y.; Ward, R. L.; Warner, J.; Was, M.; Weaver, B.; Wei, L.-W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Weßels, P.; Westphal, T.; Wette, K.; Whelan, J. T.; Whiting, B. F.; Williams, R. D.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M. H.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Woehler, J.; Worden, J.; Wright, J. L.; Wu, D. S.; Wu, G.; Yablon, J.; Yam, W.; Yamamoto, H.; Yancey, C. C.; Yu, H.; Yvert, M.; Zadrożny, A.; Zangrando, L.; Zanolin, M.; Zendri, J.-P.; Zevin, M.; Zhang, L.; Zhang, M.; Zhang, Y.; Zhao, C.; Zhou, M.; Zhou, Z.; Zhu, X. J.; Zucker, M. E.; Zuraw, S. E.; Zweizig, J.; LIGO Scientific Collaboration; Virgo Collaboration

2016-12-01

We report here the non-detection of gravitational waves from the merger of binary-neutron star systems and neutron star-black hole systems during the first observing run of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). In particular, we searched for gravitational-wave signals from binary-neutron star systems with component masses \\in [1,3] {M}⊙ and component dimensionless spins <0.05. We also searched for neutron star-black hole systems with the same neutron star parameters, black hole mass \\in [2,99] {M}⊙ , and no restriction on the black hole spin magnitude. We assess the sensitivity of the two LIGO detectors to these systems and find that they could have detected the merger of binary-neutron star systems with component mass distributions of 1.35 ± 0.13 M ⊙ at a volume-weighted average distance of ˜70 Mpc, and for neutron star-black hole systems with neutron star masses of 1.4 M ⊙ and black hole masses of at least 5 M ⊙, a volume-weighted average distance of at least ˜110 Mpc. From this we constrain with 90% confidence the merger rate to be less than 12,600 Gpc-3 yr-1 for binary-neutron star systems and less than 3600 Gpc-3 yr-1 for neutron star-black hole systems. We discuss the astrophysical implications of these results, which we find to be in conflict with only the most optimistic predictions. However, we find that if no detection of neutron star-binary mergers is made in the next two Advanced LIGO and Advanced Virgo observing runs we would place significant constraints on the merger rates. Finally, assuming a rate of {10}-7+20 Gpc-3 yr-1, short gamma-ray bursts beamed toward the Earth, and assuming that all short gamma-ray bursts have binary-neutron star (neutron star-black hole) progenitors, we can use our 90% confidence rate upper limits to constrain the beaming angle of the gamma-ray burst to be greater than 2\\buildrel{\\circ}\\over{.} {3}-1.1+1.7 (4\\buildrel{\\circ}\\over{.} {3}-1.9+3.1).

From hadrons to quarks in neutron stars: a review

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baym, Gordon; Hatsuda, Tetsuo; Kojo, Toru

In recent years our understanding of neutron stars has advanced remarkably, thanks to research converging from many directions. The importance of understanding neutron star behavior and structure has been underlined by the recent direct detection of gravitational radiation from merging neutron stars. The clean identification of several heavy neutron stars, of order two solar masses, challenges our current understanding of how dense matter can be sufficiently stiff to support such a mass against gravitational collapse. Furthermore, programs underway to determine simultaneously the mass and radius of neutron stars will continue to constrain and inform theories of neutron star interiors. Atmore » the same time, an emerging understanding in quantum chromodynamics (QCD) of how nuclear matter can evolve into deconfined quark matter at high baryon densities is leading to advances in understanding the equation of state of the matter under the extreme conditions in neutron star interiors.« less

From hadrons to quarks in neutron stars: a review

DOE PAGES

Baym, Gordon; Hatsuda, Tetsuo; Kojo, Toru; ...

2018-03-27

In recent years our understanding of neutron stars has advanced remarkably, thanks to research converging from many directions. The importance of understanding neutron star behavior and structure has been underlined by the recent direct detection of gravitational radiation from merging neutron stars. The clean identification of several heavy neutron stars, of order two solar masses, challenges our current understanding of how dense matter can be sufficiently stiff to support such a mass against gravitational collapse. Furthermore, programs underway to determine simultaneously the mass and radius of neutron stars will continue to constrain and inform theories of neutron star interiors. Atmore » the same time, an emerging understanding in quantum chromodynamics (QCD) of how nuclear matter can evolve into deconfined quark matter at high baryon densities is leading to advances in understanding the equation of state of the matter under the extreme conditions in neutron star interiors.« less

Physics of Neutron Star Crusts.

PubMed

Chamel, Nicolas; Haensel, Pawel

2008-01-01

The physics of neutron star crusts is vast, involving many different research fields, from nuclear and condensed matter physics to general relativity. This review summarizes the progress, which has been achieved over the last few years, in modeling neutron star crusts, both at the microscopic and macroscopic levels. The confrontation of these theoretical models with observations is also briefly discussed.

I-Love-Q: Unexpected Universal Relations for Neutron Stars and Quark Stars

NASA Astrophysics Data System (ADS)

Yagi, Kent; Yunes, Nicolás

2013-07-01

Neutron stars and quark stars are not only characterized by their mass and radius but also by how fast they spin, through their moment of inertia, and how much they can be deformed, through their Love number and quadrupole moment. These depend sensitively on the star’s internal structure and thus on unknown nuclear physics. We find universal relations between the moment of inertia, the Love number, and the quadrupole moment that are independent of the neutron and quark star’s internal structure. These can be used to learn about neutron star deformability through observations of the moment of inertia, break degeneracies in gravitational wave detection to measure spin in binary inspirals, distinguish neutron stars from quark stars, and test general relativity in a nuclear structure-independent fashion.

The Discovery of an Eccentric Millisecond Pulsar in the Galactic Plane

NASA Astrophysics Data System (ADS)

Champion, David J.; Ransom, Scott M.; Lazarus, Patrick; Camilo, Fernando; Kaspi, Victoria M.; Nice, David J.; Freire, Paulo C. C.; Cordes, James M.; Hessels, Jason W. T.; Bassa, Cees; Lorimer, Duncan R.; Stairs, Ingrid H.; van Leeuwen, Joeri; Arzoumnian, Zaven; Backer, Don C.; Bhat, N. D. Ramesh; Chatterjee, Shami; Crawford, Fronefield; Deneva, Julia S.; Faucher-Giguère, Claude-André; Gaensler, B. M.; Han, Jinlin; Jenet, Fredrick A.; Kasian, Laura; Kondratiev, Vlad I.; Kramer, Michael; Lazio, Joseph; McLaughlin, Maura A.; Stappers, Ben W.; Venkataraman, Arun; Vlemmings, Wouter

2008-02-01

The evolution of binary systems is governed by their orbital properties and the stellar density of the local environment. Studies of neutron stars in binary star systems offer unique insights into both these issues. In an Arecibo survey of the Galactic disk, we have found PSR J1903+0327, a radio emitting neutron star (a ``pulsar'') with a 2.15 ms rotation period, in a 95-day orbit around a massive companion. Observations in the infra-red suggests that the companion may be a main-sequence star. Theories requiring an origin in the Galactic disk cannot account for the extraordinarily high orbital eccentricity observed (0.44) or a main-sequence companion of a pulsar that has spin properties suggesting a prolonged accretion history. The most likely formation mechanism is an exchange interaction in a globular star cluster. This requires that the binary was either ejected from its parent globular cluster as a result of a three-body interaction, or that that cluster was disrupted by repeated passages through the disk of the Milky Way.

Neutron star moments of inertia

NASA Technical Reports Server (NTRS)

Ravenhall, D. G.; Pethick, C. J.

1994-01-01

An approximation for the moment of inertia of a neutron star in terms of only its mass and radius is presented, and insight into it is obtained by examining the behavior of the relativistic structural equations. The approximation is accurate to approximately 10% for a variety of nuclear equations of state, for all except very low mass stars. It is combined with information about the neutron-star crust to obtain a simple expression (again in terms only of mass and radius) for the fractional moment of inertia of the crust.

Neutron Star Spin Measurements and Dense Matter with LOFT

NASA Technical Reports Server (NTRS)

Strohmayer, Tod

2011-01-01

Observations over the last decade with RXTE have begun to reveal the X-ray binary progenitors of the fastest spinning neutron stars presently known. Detection and study of the spin rates of binary neutron stars has important implications for constraining the nature of dense matter present in neutron star interiors, as both the maximum spin rate and mass for neutron stars is set by the equation of state. Precision pulse timing of accreting neutron star binaries can enable mass constraints. Particularly promIsing is the combination of the pulse and eclipse timing, as for example, in systems like Swift 11749.4-2807. With its greater sensitivity, LOFT will enable deeper searches for the spin periods of the neutron stars, both during persistent outburst intervals and thermonuclear X-ray bursts, and enable more precise modeling of detected pulsations. I will explore the anticipated impact of LOFT on spin measurements and its potential for constraining dense matter in neutron stars

Accretion Models for Young Neutron Stars

NASA Astrophysics Data System (ADS)

Alpar, M. A.

2003-07-01

Interaction with possible fallback material, along with the magnetic fields and rotation rates at birth should determine the fates and categories of young neutron stars. This paper addresses some issues related to pure or hybrid accretion models for explaining the properties of young neutron stars.

Neutron Star Discovered Where a Black Hole Was Expected

NASA Astrophysics Data System (ADS)

2005-11-01

A very massive star collapsed to form a neutron star and not a black hole as expected, according to new results from NASA's Chandra X-ray Observatory. This discovery shows that nature has a harder time making black holes than previously thought. Scientists found this neutron star -- a dense whirling ball of neutrons about 12 miles in diameter -- in an extremely young star cluster. Astronomers were able to use well-determined properties of other stars in the cluster to deduce that the progenitor of this neutron star was at least 40 times the mass of the Sun. ESO Optical Image of Westerlund 1 ESO Optical Image of Westerlund 1 "Our discovery shows that some of the most massive stars do not collapse to form black holes as predicted, but instead form neutron stars," said Michael Muno, a UCLA postdoctoral Hubble Fellow and lead author of a paper to be published in The Astrophysical Journal Letters. When very massive stars make neutron stars and not black holes, they will have a greater influence on the composition of future generations of stars. When the star collapses to form the neutron star, more than 95% of its mass, much of which is metal-rich material from its core, is returned to the space around it. "This means that enormous amounts of heavy elements are put back into circulation and can form other stars and planets," said J. Simon Clark of the Open University in the United Kingdom. Animation: Dissolve from Optical to X-ray Image of Westerlund 1 Animation: Dissolve from Optical to X-ray Image of Westerlund 1 Astronomers do not completely understand how massive a star must be to form a black hole rather than a neutron star. The most reliable method for estimating the mass of the progenitor star is to show that the neutron star or black hole is a member of a cluster of stars, all of which are close to the same age. Because more massive stars evolve faster than less massive ones, the mass of a star can be estimated from if its evolutionary stage is known. Neutron

Galactic Sources Detected in the NuSTAR Serendipitous Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomsick, John A.; Clavel, Maïca; Chiu, Jeng-Lun

The Nuclear Spectroscopic Telescope Array (NuSTAR) provides an improvement in sensitivity at energies above 10 keV by two orders of magnitude over non-focusing satellites, making it possible to probe deeper into the Galaxy and universe. Lansbury and collaborators recently completed a catalog of 497 sources serendipitously detected in the 3–24 keV band using 13 deg{sup 2} of NuSTAR coverage. Here, we report on an optical and X-ray study of 16 Galactic sources in the catalog. We identify 8 of them as stars (but some or all could have binary companions), and use information from Gaia to report distances and X-ray luminositiesmore » for 3 of them. There are 4 CVs or CV candidates, and we argue that NuSTAR J233426–2343.9 is a relatively strong CV candidate based partly on an X-ray spectrum from XMM-Newton . NuSTAR J092418–3142.2, which is the brightest serendipitous source in the Lansbury catalog, and NuSTAR J073959–3147.8 are low-mass X-ray binary candidates, but it is also possible that these 2 sources are CVs. One of the sources is a known high-mass X-ray binary (HMXB), and NuSTAR J105008–5958.8 is a new HMXB candidate that has strong Balmer emission lines in its optical spectrum and a hard X-ray spectrum. We discuss the implications of finding these HMXBs for the surface density (log N –log S ) and luminosity function of Galactic HMXBs. We conclude that with the large fraction of unclassified sources in the Galactic plane detected by NuSTAR in the 8–24 keV band, there could be a significant population of low-luminosity HMXBs.« less

Anomalous hydrodynamics kicks neutron stars

DOE PAGES

Kaminski, Matthias; Uhlemann, Christoph F.; Bleicher, Marcus; ...

2016-06-28

Observations show that, at the beginning of their existence, neutron stars are accelerated briskly to velocities of up to a thousand kilometers per second. We argue that this remarkable effect can be explained as a manifestation of quantum anomalies on astrophysical scales. To theoretically describe the early stage in the life of neutron stars we use hydrodynamics as a systematic effective-field-theory framework. Within this framework, anomalies of the Standard Model of particle physics as underlying microscopic theory imply the presence of a particular set of transport terms, whose form is completely fixed by theoretical consistency. Here, the resulting chiral transportmore » effects in proto-neutron stars enhance neutrino emission along the internal magnetic field, and the recoil can explain the order of magnitude of the observed kick velocities.« less

Structures of rotating traditional neutron stars and hyperon stars in the relativistic σ -ω model

NASA Astrophysics Data System (ADS)

Wen, De-hua; Chen, Wei; Wang, Xian-ju; Ai, Bao-quan; Liu, Guo-tao; Dong, Dong-qiao; Liu, Liang-gang

The influence of rotation on the total masses and radii of neutron stars is calculated by Hartle's slow-rotation formalism, while the equation of state is considered in a relativistic σ -ω model. As the changes of the mass and radius of a real neutron star caused by rotation are very small in comparison with the total mass and radius, one can see that Hartle's approximate method is rational to deal with the rotating neutron stars. If three property values, mass, radius and period, are observed for the same neutron star, then the EOS of this neutron star could be decided entirely.

Homogeneous photometry and star counts in the field of 9 Galactic star clusters

NASA Astrophysics Data System (ADS)

Seleznev, A. F.; Carraro, G.; Costa, E.; Loktin, A. V.

2010-01-01

We present homogeneous V, I CCD photometry of nine stellar fields in the two inner quadrants of the Galactic plane. The lines-of-view to most of these fields aim in the direction of the very inner Galaxy, where the Galactic field is very dense, and extinction is high and patchy. Our nine fields are, according to several catalogs, centred on Galactic star clusters, namely Trumpler 13, Trumpler 20, Lynga 4, Hogg 19, Lynga 12, Trumpler 25, Trumpler 26, Ruprecht 128, and Trumpler 34. Apart from their coordinates, and in some cases additional basic data (mainly from the 2MASS archive), their properties are poorly known. By means of star count techniques and field star decontaminated Color Magnitude diagrams, the nature and size of these visual over-densities has been established; and, when possible, new cluster fundamental parameters have been derived. To strengthen our findings, we complement our data-set with JHKs photometry from the 2MASS archive, that we analyze using a suitably defined Q-parameter. Most clusters are projected towards the Carina-Sagittarium spiral arm. Because of that, we detect in the Color Magnitude diagrams of most of the other fields several distinctive sequences produced by young population within the arm. All the clusters are of intermediate or old age. The most interesting cases detected by our study are, perhaps, that of Trumpler 20, which seems to be much older than previously believed, as indicated by its prominent - and double - red clump; and that of Hogg 19, a previously overlooked old open cluster, whose existence in such regions of the Milky Way is puzzling.

Star Formation at the Galactic Center

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-08-01

Could stars be forming in the inhospitable environment near Sagittarius A* in the heart of the Milky Way? A possible signature of low-mass star formation has recently been found just two light-years from the black hole at the center of our galaxy — a region that was previously thought to be too hostile for such activity. Searching for Signatures: Previous observations of the central few light-years of the Milky Way had focused on a population of about 200 massive, young and very bright stars in tight orbits around Sgr A*. These stars are only a few million years old and prompted scientists to wonder: have they somehow managed to form in situ, in spite of their close proximity to the black hole, or did they form further out and then migrate in? Motivated by this mystery, Farhad Yusef-Zadeh of Northwestern University and collaborators looked for evidence of even younger stars close to Sagittarius A*, which would demonstrate that star formation in the area is an ongoing process. Using the Very Large Array (VLA), the collaboration discovered several small sources in one arm of activity near Sgr A*. This 34-GHz image provides a close-up view of two protoplanetary disk candidates (labeled P26 and P8) located near Sgr A*. These objects are outlined on the right side by a bow shock caused by impacting stellar wind that streams from the young, hot stars closer to the Galactic center. The disks are thought to contain recently-formed, low-mass stars. (Credit: Yusef-Zadeh et al., 2015) Heated Disks: The team identified these sources as candidate photoevaporative protoplanetary disks, or “proplyds” — areas of dense, ionized gas and dust surrounding young, newly formed stars. The proplyd candidates are between 10,000 and 100,000 years old, and they lie along the edge of a large molecular cloud. It is likely that this cloud produced the disks by providing a reservoir of gas to feed the star-formation activity. The region surrounding these proplyds is blasted with harsh

The Galactic Distribution of Massive Star Formation from the Red MSX Source Survey

NASA Astrophysics Data System (ADS)

Figura, Charles C.; Urquhart, J. S.

2013-01-01

Massive stars inject enormous amounts of energy into their environments in the form of UV radiation and molecular outflows, creating HII regions and enriching local chemistry. These effects provide feedback mechanisms that aid in regulating star formation in the region, and may trigger the formation of subsequent generations of stars. Understanding the mechanics of massive star formation presents an important key to understanding this process and its role in shaping the dynamics of galactic structure. The Red MSX Source (RMS) survey is a multi-wavelength investigation of ~1200 massive young stellar objects (MYSO) and ultra-compact HII (UCHII) regions identified from a sample of colour-selected sources from the Midcourse Space Experiment (MSX) point source catalog and Two Micron All Sky Survey. We present a study of over 900 MYSO and UCHII regions investigated by the RMS survey. We review the methods used to determine distances, and investigate the radial galactocentric distribution of these sources in context with the observed structure of the galaxy. The distribution of MYSO and UCHII regions is found to be spatially correlated with the spiral arms and galactic bar. We examine the radial distribution of MYSOs and UCHII regions and find variations in the star formation rate between the inner and outer Galaxy and discuss the implications for star formation throughout the galactic disc.

Starquakes, Heating Anomalies, and Nuclear Reactions in the Neutron Star Crust

NASA Astrophysics Data System (ADS)

Deibel, Alex Thomas

When the most massive stars perish, their cores may remain intact in the form of extremely dense and compact stars. These stellar remnants, called neutron stars, are on the cusp of becoming black holes and reach mass densities greater than an atomic nucleus in their centers. Although the interiors of neutron stars were difficult to investigate at the time of their discovery, the advent of modern space-based telescopes (e.g., Chandra X-ray Observatory) has pushed our understanding of the neutron star interior into exciting new realms. It has been shown that the neutron star interior spans an enormous range of densities and contains many phases of matter, and further theoretical progress must rely on numerical calculations of neutron star phenomena built with detailed nuclear physics input. To further investigate the properties of the neutron star interior, this dissertation constructs numerical models of neutron stars, applies models to various observations of neutron star high-energy phenomena, and draws new conclusions about the neutron star interior from these analyses. In particular, we model the neutron star's outermost ? 1 km that encompasses the neutron star's envelope, ocean, and crust. The model must implement detailed nuclear physics to properly simulate the hydrostatic and thermal structure of the neutron star. We then apply our model to phenomena that occur in these layers, such as: thermonuclear bursts in the envelope, g-modes in the ocean, torsional oscillations of the crust, and crust cooling of neutron star transients. A comparison of models to observations provides new insights on the properties of dense matter that are often difficult to probe through terrestrial experiments. For example, models of the quiescent cooling of neutron stars, such as the accreting transient MAXI J0556-332, at late times into quiescence probe the thermal transport properties of the deep neutron star crust. This modeling provides independent data from astronomical

Neutron star news and puzzles

NASA Astrophysics Data System (ADS)

Prakash, Madappa

2014-08-01

Gerry Brown has had the most influence on my career in Physics, and my life after graduate studies. This article gives a brief account of some of the many ways in which Gerry shaped my research. Focus is placed on the significant strides on neutron star research made by the group at Stony Brook, which Gerry built from scratch. Selected puzzles about neutron stars that remain to be solved are noted.

Burst Oscillations: A New Spin on Neutron Stars

NASA Technical Reports Server (NTRS)

Strohmayer, Tod

2007-01-01

Observations with NASA's Rossi X-ray Timing Explorer (RXTE) have shown that the X-ray flux during thermonuclear X-ray bursts fr-om accreting neutron stars is often strongly pulsed at frequencies as high as 620 Hz. We now know that these oscillations are produced by spin modulation of the thermonuclear flux from the neutron star surface. In addition to revealing the spin frequency, they provide new ways to probe the properties and physics of accreting neutron stars. I will briefly review our current observational and theoretical understanding of these oscillations and discuss what they are telling us about neutron stars.

New Galactic Candidate Luminous Blue Variables and Wolf-Rayet Stars

NASA Astrophysics Data System (ADS)

Stringfellow, Guy S.; Gvaramadze, Vasilii V.; Beletsky, Yuri; Kniazev, Alexei Y.

2012-04-01

We have undertaken a near-infrared spectral survey of stars associated with compact mid-IR shells recently revealed by the MIPSGAL (24 μm) and GLIMPSE (8 μm) Spitzer surveys, whose morphologies are typical of circumstellar shells produced by massive evolved stars. Through spectral similarity with known Luminous Blue Variable (LBV) and Wolf-Rayet (WR) stars, a large population of candidate LBVs (cLBVs) and a smaller number of new WR stars are being discovered. This significantly increases the Galactic cLBV population and confirms that nebulae are inherent to most (if not all) objects of this class.

On the illumination of neutron star accretion discs

NASA Astrophysics Data System (ADS)

Wilkins, D. R.

2018-03-01

The illumination of the accretion disc in a neutron star X-ray binary by X-rays emitted from (or close to) the neutron star surface is explored through general relativistic ray tracing simulations. The applicability of the canonical suite of relativistically broadened emission line models (developed for black holes) to discs around neutron stars is evaluated. These models were found to describe well emission lines from neutron star accretion discs unless the neutron star radius is larger than the innermost stable orbit of the accretion disc at 6 rg or the disc is viewed at high inclination, above 60° where shadowing of the back side of the disc becomes important. Theoretical emissivity profiles were computed for accretion discs illuminated by hotspots on the neutron star surfaces, bands of emission and emission by the entirety of the hot, spherical star surface and in all cases, the emissivity profile of the accretion disc was found to be well represented by a single power law falling off slightly steeper than r-3. Steepening of the emissivity index was found where the emission is close to the disc plane and the disc can appear truncated when illuminated by a hotspot at high latitude. The emissivity profile of the accretion disc in Serpens X-1 was measured and found to be consistent with a single unbroken power law with index q=3.5_{-0.4}^{+0.3}, suggestive of illumination by the boundary layer between the disc and neutron star surface.

On Fallback Disks around Young Neutron Stars

NASA Astrophysics Data System (ADS)

Alpar, M. Ali; Ertan, Ü.; Erkut, M. H.

2006-08-01

Some bound matter in the form of a fallback disk may be an initial parameter of isolated neutron stars at birth, which, along with the initial rotation rate and dipole (and higher multipole) magnetic moments, determines the evolution of neutron stars and the categories into which they fall. This talk reviews the possibilities of fallback disk models in explaining properties of isolated neutron stars of different categories. Recent observations of a fallback disk and observational limits on fallback disks will also be discussed.

Binary stars in the Galactic thick disc

NASA Astrophysics Data System (ADS)

Izzard, Robert G.; Preece, Holly; Jofre, Paula; Halabi, Ghina M.; Masseron, Thomas; Tout, Christopher A.

2018-01-01

The combination of asteroseismologically measured masses with abundances from detailed analyses of stellar atmospheres challenges our fundamental knowledge of stars and our ability to model them. Ancient red-giant stars in the Galactic thick disc are proving to be most troublesome in this regard. They are older than 5 Gyr, a lifetime corresponding to an initial stellar mass of about 1.2 M⊙. So why do the masses of a sizeable fraction of thick-disc stars exceed 1.3 M⊙, with some as massive as 2.3 M⊙? We answer this question by considering duplicity in the thick-disc stellar population using a binary population-nucleosynthesis model. We examine how mass transfer and merging affect the stellar mass distribution and surface abundances of carbon and nitrogen. We show that a few per cent of thick-disc stars can interact in binary star systems and become more massive than 1.3 M⊙. Of these stars, most are single because they are merged binaries. Some stars more massive than 1.3 M⊙ form in binaries by wind mass transfer. We compare our results to a sample of the APOKASC data set and find reasonable agreement except in the number of these thick-disc stars more massive than 1.3 M⊙. This problem is resolved by the use of a logarithmically flat orbital-period distribution and a large binary fraction.

Planets Around Neutron Stars

NASA Technical Reports Server (NTRS)

Wolszczan, Alexander; Kulkarni, Shrinivas R; Anderson, Stuart B.

2003-01-01

The objective of this proposal was to continue investigations of neutron star planetary systems in an effort to describe and understand their origin, orbital dynamics, basic physical properties and their relationship to planets around normal stars. This research represents an important element of the process of constraining the physics of planet formation around various types of stars. The research goals of this project included long-term timing measurements of the planets pulsar, PSR B1257+12, to search for more planets around it and to study the dynamics of the whole system, and sensitive searches for millisecond pulsars to detect further examples of old, rapidly spinning neutron stars with planetary systems. The instrumentation used in our project included the 305-m Arecibo antenna with the Penn State Pulsar Machine (PSPM), the 100-m Green Bank Telescope with the Berkeley- Caltech Pulsar Machine (BCPM), and the 100-m Effelsberg and 64-m Parkes telescopes equipped with the observatory supplied backend hardware.

Intense electromagnetic outbursts from collapsing hypermassive neutron stars

NASA Astrophysics Data System (ADS)

Lehner, Luis; Palenzuela, Carlos; Liebling, Steven L.; Thompson, Christopher; Hanna, Chad

2012-11-01

We study the gravitational collapse of a magnetized neutron star using a novel numerical approach able to capture both the dynamics of the star and the behavior of the surrounding plasma. In this approach, a fully general relativistic magnetohydrodynamics implementation models the collapse of the star and provides appropriate boundary conditions to a force-free model which describes the stellar exterior. We validate this strategy by comparing with known results for the rotating monopole and aligned rotator solutions and then apply it to study both rotating and nonrotating stellar collapse scenarios and contrast the behavior with what is obtained when employing the electrovacuum approximation outside the star. The nonrotating electrovacuum collapse is shown to agree qualitatively with a Newtonian model of the electromagnetic field outside a collapsing star. We illustrate and discuss a fundamental difference between the force-free and electrovacuum solutions, involving the appearance of large zones of electric-dominated field in the vacuum case. This provides a clear demonstration of how dissipative singularities appear generically in the nonlinear time evolution of force-free fluids. In both the rotating and nonrotating cases, our simulations indicate that the collapse induces a strong electromagnetic transient, which leaves behind an uncharged, unmagnetized Kerr black hole. In the case of submillisecond rotation, the magnetic field experiences strong winding, and the transient carries much more energy. This result has important implications for models of gamma-ray bursts. Even when the neutron star is surrounded by an accretion torus (as in binary merger and collapsar scenarios), a magnetosphere may emerge through a dynamo process operating in a surface shear layer. When this rapidly rotating magnetar collapses to a black hole, the electromagnetic energy released can compete with the later output in a Blandford-Znajek jet. Much less electromagnetic energy is

Gamma Rays from the Galactic Bulge and Large Extra Dimensions

NASA Astrophysics Data System (ADS)

Cassé, Michel; Paul, Jacques; Bertone, Gianfranco; Sigl, Günter

2004-03-01

An intriguing feature of extra dimensions is the possible production of Kaluza Klein gravitons by nucleon-nucleon bremsstrahlung, in the course of core collapse of massive stars, with gravitons then being trapped around the newly born neutron stars and decaying into two gamma rays, making neu­tron stars gamma-ray sources. We strengthen the limits on the radius of compactification of extra dimensions for a small number n of them, or alternatively the fundamental scale of quantum gravity, considering the gamma-ray emission of the whole population of neutron stars sitting in the Galactic bulge, instead of the closest member of this category. For n=1 the constraint on the compactification radius is R<400 μm.

A and F stars as probes of outer Galactic disc kinematics

NASA Astrophysics Data System (ADS)

Harris, A.; Drew, J. E.; Farnhill, H. J.; Monguió, M.; Gebran, M.; Wright, N. J.; Drake, J. J.; Sale, S. E.

2018-04-01

Previous studies of the rotation law in the outer Galactic disc have mainly used gas tracers or clump giants. Here, we explore A and F stars as alternatives: these provide a much denser sampling in the outer disc than gas tracers and have experienced significantly less velocity scattering than older clump giants. This first investigation confirms the suitability of A stars in this role. Our work is based on spectroscopy of ˜1300 photometrically selected stars in the red calcium-triplet region, chosen to mitigate against the effects of interstellar extinction. The stars are located in two low Galactic latitude sightlines, at longitudes ℓ = 118°, sampling strong Galactic rotation shear, and ℓ = 178°, near the anticentre. With the use of Markov Chain Monte Carlo parameter fitting, stellar parameters and radial velocities are measured, and distances computed. The obtained trend of radial velocity with distance is inconsistent with existing flat or slowly rising rotation laws from gas tracers (Brand & Blitz 1993; Reid et al. 2014). Instead, our results fit in with those obtained by Huang et al. (2016) from disc clump giants that favoured rising circular speeds. An alternative interpretation in terms of spiral arm perturbation is not straight forward. We assess the role that undetected binaries in the sample and distance error may have in introducing bias, and show that the former is a minor factor. The random errors in our trend of circular velocity are within ±5 km s-1.

The Open Cluster Chemical Abundances and Mapping (OCCAM) Survey: Galactic Neutron Capture Abundance Gradients

NASA Astrophysics Data System (ADS)

O'Connell, Julia; Frinchaboy, Peter M.; Shetrone, Matthew D.; Melendez, Matthew; Cunha, Katia M. L.; Majewski, Steven R.; Zasowski, Gail; APOGEE Team

2017-01-01

The evolution of elements, as a function or age, throughout the Milky Way disk provides a key constraint for galaxy evolution models. In an effort to provide these constraints, we have conducted an investigation into the r- and s- process elemental abundances for a large sample of open clusters as part of an optical follow-up to the SDSS-III/APOGEE-1 survey. Stars were identified as cluster members by the Open Cluster Chemical Abundance & Mapping (OCCAM) survey, which culls member candidates by radial velocity, metallicity, and proper motion from the observed APOGEE sample. To obtain data for neutron capture elements in these clusters, we conducted a long-term observing campaign covering three years (2013-2016) using the McDonald Observatory Otto Struve 2.1-m telescope and Sandiford Cass Echelle Spectrograph (R ~ 60,000). We present Galactic neutron-capture abundance gradients using 30+ clusters, within 6 kpc of the Sun, covering a range of ages from ~80 Myr to ~10 Gyr .

The Open Cluster Chemical Abundances and Mapping (OCCAM) Survey: Galactic Neutron CaptureAbundance Gradients

NASA Astrophysics Data System (ADS)

O'Connell, Julia; Frinchaboy, Peter M.; Shetrone, Matthew D.; Melendez, Matthew; Cunha, Katia; Majewski, Steven R.; Zasowski, Gail; APOGEE Team

2017-06-01

The evolution of elements, as a function or age, throughout the Milky Way disk provides a key constraint for galaxy evolution models. In an effort to provide these constraints, we have conducted an investigation into the r- and s- process elemental abundances for a large sample of open clusters as part of an optical follow-up to the SDSS-III/APOGEE-1 survey. Stars were identified as cluster members by the Open Cluster Chemical Abundance & Mapping (OCCAM) survey, which culls member candidates by radial velocity, metallicity and proper motion from the observed APOGEE sample. To obtain data for neutron capture elements in these clusters, we conducted a long-term observing campaign covering three years (2013-2016) using the McDonald Observatory Otto Struve 2.1-m telescope and Sandiford Cass Echelle Spectrograph (R ~ 60,000). We present Galactic neutron capture abundance gradients using 30+ clusters, within 6 kpc of the Sun, covering a range of ages from ~80 Myr to ~10 Gyr .

Neutrino Processes in Neutron Stars

NASA Astrophysics Data System (ADS)

Kolomeitsev, E. E.; Voskresensky, D. N.

2010-10-01

The aim of these lectures is to introduce basic processes responsible for cooling of neutron stars and to show how to calculate the neutrino production rate in dense strongly interacting nuclear medium. The formalism is presented that treats on equal footing one-nucleon and multiple-nucleon processes and reactions with virtual bosonic modes and condensates. We demonstrate that neutrino emission from dense hadronic component in neutron stars is subject of strong modifications due to collective effects in the nuclear matter. With the most important in-medium processes incorporated in the cooling code an overall agreement with available soft X ray data can be easily achieved. With these findings the so-called “standard” and “non-standard” cooling scenarios are replaced by one general “nuclear medium cooling scenario” which relates slow and rapid neutron star coolings to the star masses (interior densities). The lectures are split in four parts. Part I: After short introduction to the neutron star cooling problem we show how to calculate neutrino reaction rates of the most efficient one-nucleon and two-nucleon processes. No medium effects are taken into account in this instance. The effects of a possible nucleon pairing are discussed. We demonstrate that the data on neutron star cooling cannot be described without inclusion of medium effects. It motivates an assumption that masses of the neutron stars are different and that neutrino reaction rates should be strongly density dependent. Part II: We introduce the Green’s function diagram technique for systems in and out of equilibrium and the optical theorem formalism. The latter allows to perform calculations of production rates with full Green’s functions including all off-mass-shell effects. We demonstrate how this formalism works within the quasiparticle approximation. Part III: The basic concepts of the nuclear Fermi liquid approach are introduced. We show how strong interaction effects can be

Gravitational radiation from rapidly rotating nascent neutron stars

NASA Technical Reports Server (NTRS)

Lai, Dong; Shapiro, Stuart L.

1995-01-01

We study the secular evolution and gravitational wave signature of a newly formed, rapidly rotating neutron star. The neutron star may arise from core collapse in a massive star or from the accretion-induced collapse of a white dwarf. After a brief dynamical phase, the nascent neutron star settles into an axisymmetric, secularly unstable state. Gravitational radiation drives the star to a nonaxisymmetric, stationary equilibrium configuration via the bar-mode instability. The emitted quasi-periodic gravitational waves have a unique signature: the wave frequency sweeps downward from a few hundred Hertz to zero, while the wave amplitude increase from zero to a maximum and then decays back to zero. Such a wave signal could detected by broadband gravitational wave interferometers currently being constructed. We also characterize two other types of gravitational wave signals that could arise in principle from a rapidly rotating, secularly unstable neutron star: a high-frequency (f greater than or approximately = 1000 Hz) wave which increases the pattern-speed of the star, and a wave that actually increases the angular momentum of the star.

Neutron Star Interior Composition Explorer (NICE)

NASA Technical Reports Server (NTRS)

Gendreau, Keith C.; Arzoumanian, Zaven

2008-01-01

This viewgraph presentation contains an overview of the mission of the Neutron Star Interior Composition Explorer (NICE), a proposed International Space Station (ISS) payload dedicated ot the study of neutron stars. There are also reviews of the Science Objectives of the payload,the science measurements, the design and the expected performance for the instruments for NICE,

Optical-NIR dust extinction towards Galactic O stars

NASA Astrophysics Data System (ADS)

Maíz Apellániz, J.; Barbá, R. H.

2018-05-01

Context. O stars are excellent tracers of the intervening ISM because of their high luminosity, blue intrinsic SED, and relatively featureless spectra. We are currently conducting the Galactic O-Star Spectroscopic Survey (GOSSS), which is generating a large sample of O stars with accurate spectral types within several kpc of the Sun. Aims: We aim to obtain a global picture of the properties of dust extinction in the solar neighborhood based on optical-NIR photometry of O stars with accurate spectral types. Methods: We have processed a carefully selected photometric set with the CHORIZOS code to measure the amount [E(4405 - 5495)] and type [R5495] of extinction towards 562 O-type stellar systems. We have tested three different families of extinction laws and analyzed our results with the help of additional archival data. Results: The Maíz Apellániz et al. (2014, A&A, 564, A63) family of extinction laws provides a better description of Galactic dust that either the Cardelli et al. (1989, ApJ, 345, 245) or Fitzpatrick (1999, PASP, 111, 63) families, so it should be preferentially used when analysing samples similar to the one in this paper. In many cases O stars and late-type stars experience similar amounts of extinction at similar distances but some O stars are located close to the molecular clouds left over from their births and have larger extinctions than the average for nearby late-type populations. In qualitative terms, O stars experience a more diverse extinction than late-type stars, as some are affected by the small-grain-size, low-R5495 effect of molecular clouds and others by the large-grain-size, high-R5495 effect of H II regions. Late-type stars experience a narrower range of grain sizes or R5495, as their extinction is predominantly caused by the average, diffuse ISM. We propose that the reason for the existence of large-grain-size, high-R5495 regions in the ISM in the form of H II regions and hot-gas bubbles is the selective destruction of small dust

Astronomers Discover Most Massive Neutron Star Yet Known

NASA Astrophysics Data System (ADS)

2010-10-01

Astronomers using the National Science Foundation's Green Bank Telescope (GBT) have discovered the most massive neutron star yet found, a discovery with strong and wide-ranging impacts across several fields of physics and astrophysics. "This neutron star is twice as massive as our Sun. This is surprising, and that much mass means that several theoretical models for the internal composition of neutron stars now are ruled out," said Paul Demorest, of the National Radio Astronomy Observatory (NRAO). "This mass measurement also has implications for our understanding of all matter at extremely high densities and many details of nuclear physics," he added. Neutron stars are the superdense "corpses" of massive stars that have exploded as supernovae. With all their mass packed into a sphere the size of a small city, their protons and electrons are crushed together into neutrons. A neutron star can be several times more dense than an atomic nucleus, and a thimbleful of neutron-star material would weigh more than 500 million tons. This tremendous density makes neutron stars an ideal natural "laboratory" for studying the most dense and exotic states of matter known to physics. The scientists used an effect of Albert Einstein's theory of General Relativity to measure the mass of the neutron star and its orbiting companion, a white dwarf star. The neutron star is a pulsar, emitting lighthouse-like beams of radio waves that sweep through space as it rotates. This pulsar, called PSR J1614-2230, spins 317 times per second, and the companion completes an orbit in just under nine days. The pair, some 3,000 light-years distant, are in an orbit seen almost exactly edge-on from Earth. That orientation was the key to making the mass measurement. As the orbit carries the white dwarf directly in front of the pulsar, the radio waves from the pulsar that reach Earth must travel very close to the white dwarf. This close passage causes them to be delayed in their arrival by the distortion of

The spin evolution of nascent neutron stars

NASA Astrophysics Data System (ADS)

Watts, Anna L.; Andersson, Nils

2002-07-01

The loss of angular momentum owing to unstable r-modes in hot young neutron stars has been proposed as a mechanism for achieving the spin rates inferred for young pulsars. One factor that could have a significant effect on the action of the r-mode instability is fallback of supernova remnant material. The associated accretion torque could potentially counteract any gravitational-wave-induced spin-down, and accretion heating could affect the viscous damping rates and hence the instability. We discuss the effects of various external agents on the r-mode instability scenario within a simple model of supernova fallback on to a hot young magnetized neutron star. We find that the outcome depends strongly on the strength of the magnetic field of the star. Our model is capable of generating spin rates for young neutron stars that accord well with initial spin rates inferred from pulsar observations. The combined action of r-mode instability and fallback appears to cause the spin rates of neutron stars born with very different spin rates to converge, on a time-scale of approximately 1 year. The results suggest that stars with magnetic fields <=1013G could emit a detectable gravitational wave signal for perhaps several years after the supernova event. Stars with higher fields (magnetars) are unlikely to emit a detectable gravitational wave signal via the r-mode instability. The model also suggests that the r-mode instability could be extremely effective in preventing young neutron stars from going dynamically unstable to the bar-mode.

From Supernovae to Neutron Stars

NASA Astrophysics Data System (ADS)

Suwa, Yudai

A core-collapse supernova is a generation site of a neutron star as well as one of the largest explosions in the universe. This article gives a brief overview of the studies on supernova explosion mechanism. Basic picture of the explosion mechanism, the method to solve neutrino transfer equation, the impact of the nuclear equation of state on the explosion, and long-term simulation of neutron star evolution from the onset of the explosion are presented.

Detecting dark matter with imploding pulsars in the galactic center.

PubMed

Bramante, Joseph; Linden, Tim

2014-11-07

The paucity of old millisecond pulsars observed at the galactic center of the Milky Way could be the result of dark matter accumulating in and destroying neutron stars. In regions of high dark matter density, dark matter clumped in a pulsar can exceed the Schwarzschild limit and collapse into a natal black hole which destroys the pulsar. We examine what dark matter models are consistent with this hypothesis and find regions of parameter space where dark matter accumulation can significantly degrade the neutron star population within the galactic center while remaining consistent with observations of old millisecond pulsars in globular clusters and near the solar position. We identify what dark matter couplings and masses might cause a young pulsar at the galactic center to unexpectedly extinguish. Finally, we find that pulsar collapse age scales inversely with the dark matter density and linearly with the dark matter velocity dispersion. This implies that maximum pulsar age is spatially dependent on position within the dark matter halo of the Milky Way. In turn, this pulsar age spatial dependence will be dark matter model dependent.

VERY METAL-POOR STARS IN THE OUTER GALACTIC BULGE FOUND BY THE APOGEE SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garcia Perez, Ana E.; Majewski, Steven R.; Hearty, Fred R.

2013-04-10

Despite its importance for understanding the nature of early stellar generations and for constraining Galactic bulge formation models, at present little is known about the metal-poor stellar content of the central Milky Way. This is a consequence of the great distances involved and intervening dust obscuration, which challenge optical studies. However, the Apache Point Observatory Galactic Evolution Experiment (APOGEE), a wide-area, multifiber, high-resolution spectroscopic survey within Sloan Digital Sky Survey III, is exploring the chemistry of all Galactic stellar populations at infrared wavelengths, with particular emphasis on the disk and the bulge. An automated spectral analysis of data on 2403more » giant stars in 12 fields in the bulge obtained during APOGEE commissioning yielded five stars with low metallicity ([Fe/H] {<=} -1.7), including two that are very metal-poor [Fe/H] {approx} -2.1 by bulge standards. Luminosity-based distance estimates place the 5 stars within the outer bulge, where 1246 of the other analyzed stars may reside. A manual reanalysis of the spectra verifies the low metallicities, and finds these stars to be enhanced in the {alpha}-elements O, Mg, and Si without significant {alpha}-pattern differences with other local halo or metal-weak thick-disk stars of similar metallicity, or even with other more metal-rich bulge stars. While neither the kinematics nor chemistry of these stars can yet definitively determine which, if any, are truly bulge members, rather than denizens of other populations co-located with the bulge, the newly identified stars reveal that the chemistry of metal-poor stars in the central Galaxy resembles that of metal-weak thick-disk stars at similar metallicity.« less

From hadrons to quarks in neutron stars: a review.

PubMed

Baym, Gordon; Hatsuda, Tetsuo; Kojo, Toru; Powell, Philip D; Song, Yifan; Takatsuka, Tatsuyuki

2018-05-01

In recent years our understanding of neutron stars has advanced remarkably, thanks to research converging from many directions. The importance of understanding neutron star behavior and structure has been underlined by the recent direct detection of gravitational radiation from merging neutron stars. The clean identification of several heavy neutron stars, of order two solar masses, challenges our current understanding of how dense matter can be sufficiently stiff to support such a mass against gravitational collapse. Programs underway to determine simultaneously the mass and radius of neutron stars will continue to constrain and inform theories of neutron star interiors. At the same time, an emerging understanding in quantum chromodynamics (QCD) of how nuclear matter can evolve into deconfined quark matter at high baryon densities is leading to advances in understanding the equation of state of the matter under the extreme conditions in neutron star interiors. We review here the equation of state of matter in neutron stars from the solid crust through the liquid nuclear matter interior to the quark regime at higher densities. We focus in detail on the question of how quark matter appears in neutron stars, and how it affects the equation of state. After discussing the crust and liquid nuclear matter in the core we briefly review aspects of microscopic quark physics relevant to neutron stars, and quark models of dense matter based on the Nambu-Jona-Lasinio framework, in which gluonic processes are replaced by effective quark interactions. We turn then to describing equations of state useful for interpretation of both electromagnetic and gravitational observations, reviewing the emerging picture of hadron-quark continuity in which hadronic matter turns relatively smoothly, with at most only a weak first order transition, into quark matter with increasing density. We review construction of unified equations of state that interpolate between the reasonably well

From hadrons to quarks in neutron stars: a review

NASA Astrophysics Data System (ADS)

Baym, Gordon; Hatsuda, Tetsuo; Kojo, Toru; Powell, Philip D.; Song, Yifan; Takatsuka, Tatsuyuki

2018-05-01

In recent years our understanding of neutron stars has advanced remarkably, thanks to research converging from many directions. The importance of understanding neutron star behavior and structure has been underlined by the recent direct detection of gravitational radiation from merging neutron stars. The clean identification of several heavy neutron stars, of order two solar masses, challenges our current understanding of how dense matter can be sufficiently stiff to support such a mass against gravitational collapse. Programs underway to determine simultaneously the mass and radius of neutron stars will continue to constrain and inform theories of neutron star interiors. At the same time, an emerging understanding in quantum chromodynamics (QCD) of how nuclear matter can evolve into deconfined quark matter at high baryon densities is leading to advances in understanding the equation of state of the matter under the extreme conditions in neutron star interiors. We review here the equation of state of matter in neutron stars from the solid crust through the liquid nuclear matter interior to the quark regime at higher densities. We focus in detail on the question of how quark matter appears in neutron stars, and how it affects the equation of state. After discussing the crust and liquid nuclear matter in the core we briefly review aspects of microscopic quark physics relevant to neutron stars, and quark models of dense matter based on the Nambu–Jona–Lasinio framework, in which gluonic processes are replaced by effective quark interactions. We turn then to describing equations of state useful for interpretation of both electromagnetic and gravitational observations, reviewing the emerging picture of hadron-quark continuity in which hadronic matter turns relatively smoothly, with at most only a weak first order transition, into quark matter with increasing density. We review construction of unified equations of state that interpolate between the reasonably well

Neutrino-heated stars and broad-line emission from active galactic nuclei

NASA Technical Reports Server (NTRS)

Macdonald, James; Stanev, Todor; Biermann, Peter L.

1991-01-01

Nonthermal radiation from active galactic nuclei indicates the presence of highly relativistic particles. The interaction of these high-energy particles with matter and photons gives rise to a flux of high-energy neutrinos. In this paper, the influence of the expected high neutrino fluxes on the structure and evolution of single, main-sequence stars is investigated. Sequences of models of neutrino-heated stars in thermal equilibrium are presented for masses 0.25, 0.5, 0.8, and 1.0 solar mass. In addition, a set of evolutionary sequences for mass 0.5 solar mass have been computed for different assumed values for the incident neutrino energy flux. It is found that winds driven by the heating due to high-energy particles and hard electromagnetic radiation of the outer layers of neutrino-bloated stars may satisfy the requirements of the model of Kazanas (1989) for the broad-line emission clouds in active galactic nuclei.

The OGLE Collection of Variable Stars. Classical, Type II, and Anomalous Cepheids toward the Galactic Center

NASA Astrophysics Data System (ADS)

Soszyński, I.; Udalski, A.; Szymański, M. K.; Wyrzykowski, Ł.; Ulaczyk, K.; Poleski, R.; Pietrukowicz, P.; Kozłowski, S.; Skowron, D. M.; Skowron, J.; Mróz, P.; Pawlak, M.; Rybicki, K.; Jacyszyn-Dobrzeniecka, A.

2017-12-01

We present a collection of classical, typeII, and anomalous Cepheids detected in the OGLE fields toward the Galactic center. The sample contains 87 classical Cepheids pulsating in one, two or three radial modes, 924 type II Cepheids divided into BL Her, W Vir, peculiar W Vir, and RV Tau stars, and 20 anomalous Cepheids - first such objects found in the Galactic bulge. Additionally, we upgrade the OGLE Collection of RR Lyr stars in the Galactic bulge by adding 828 newly identified variables. For all Cepheids and RRLyr stars, we publish time-series VI photometry obtained during the OGLE-IV project, from 2010 through 2017. We discuss basic properties of our classical pulsators: their spatial distribution, light curve morphology, period-luminosity relations, and position in the Petersen diagram. We present the most interesting individual objects in our collection: a typeII Cepheid with additional eclipsing modulation, WVir stars with the period doubling effect and the RVb phenomenon, a mode-switching RR Lyr star, and a triple-mode anomalous RRd star.

Tidal Love Numbers of Neutron Stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hinderer, Tanja

For a variety of fully relativistic polytropic neutron star models we calculate the star's tidal Love number k{sub 2}. Most realistic equations of state for neutron stars can be approximated as a polytrope with an effective index n {approx} 0.5-1.0. The equilibrium stellar model is obtained by numerical integration of the Tolman-Oppenheimer-Volkhov equations. We calculate the linear l = 2 static perturbations to the Schwarzschild spacetime following the method of Thorne and Campolattaro. Combining the perturbed Einstein equations into a single second-order differential equation for the perturbation to the metric coefficient g{sub tt} and matching the exterior solution to themore » asymptotic expansion of the metric in the star's local asymptotic rest frame gives the Love number. Our results agree well with the Newtonian results in the weak field limit. The fully relativistic values differ from the Newtonian values by up to {approx}24%. The Love number is potentially measurable in gravitational wave signals from inspiralling binary neutron stars.« less

The Mystery of the Lonely Neutron Star

NASA Astrophysics Data System (ADS)

2000-09-01

The VLT Reveals Bowshock Nebula around RX J1856.5-3754 Deep inside the Milky Way, an old and lonely neutron star plows its way through interstellar space. Known as RX J1856.5-3754 , it measures only ~ 20 km across. Although it is unusually hot for its age, about 700,000 °C, earlier observations did not reveal any activity at all, contrary to all other neutron stars known so far. In order to better understand this extreme type of object, a detailed study of RX J1856.5-3754 was undertaken by Marten van Kerkwijk (Institute of Astronomy of the University of Utrecht, The Netherlands) and Shri Kulkarni (California Institute of Technology, Pasadena, California, USA). To the astronomers' delight and surprise, images and spectra obtained with the ESO Very Large Telescope (VLT) now show a small nearby cone-shaped ("bowshock") nebula. It shines in the light from hydrogen atoms and is obviously a product of some kind of interaction with this strange star. Neutron stars - remnants of supernova explosions Neutron stars are among the most extreme objects in the Universe. They are formed when a massive star dies in a "supernova explosion" . During this dramatic event, the core of the star suddenly collapses under its own weight and the outer parts are violently ejected into surrounding space. One of the best known examples is the Crab Nebula in the constellation Taurus (The Bull). It is the gaseous remnant of a star that exploded in the year 1054 and also left behind a pulsar , i.e., a rotating neutron star [1]. A supernova explosion is a very complex event that is still not well understood. Nor is the structure of a neutron star known in any detail. It depends on the extreme properties of matter that has been compressed to incredibly high densities, far beyond the reach of physics experiments on Earth [2]. The ultimate fate of a neutron star is also unclear. From the observed rates of supernova explosions in other galaxies, it appears that several hundred million neutron stars

General relativistic viscous hydrodynamics of differentially rotating neutron stars

NASA Astrophysics Data System (ADS)

Shibata, Masaru; Kiuchi, Kenta; Sekiguchi, Yu-ichiro

2017-04-01

Employing a simplified version of the Israel-Stewart formalism for general-relativistic shear-viscous hydrodynamics, we perform axisymmetric general-relativistic simulations for a rotating neutron star surrounded by a massive torus, which can be formed from differentially rotating stars. We show that with our choice of a shear-viscous hydrodynamics formalism, the simulations can be stably performed for a long time scale. We also demonstrate that with a possibly high shear-viscous coefficient, not only viscous angular momentum transport works but also an outflow could be driven from a hot envelope around the neutron star for a time scale ≳100 ms with the ejecta mass ≳10-2 M⊙ , which is comparable to the typical mass for dynamical ejecta of binary neutron-star mergers. This suggests that massive neutron stars surrounded by a massive torus, which are typical outcomes formed after the merger of binary neutron stars, could be the dominant source for providing neutron-rich ejecta, if the effective shear viscosity is sufficiently high, i.e., if the viscous α parameter is ≳10-2. The present numerical result indicates the importance of a future high-resolution magnetohydrodynamics simulation that is the unique approach to clarify the viscous effect in the merger remnants of binary neutron stars by the first-principle manner.

Magnetized Neutron Stars in the Interstellar Medium

NASA Astrophysics Data System (ADS)

Toropina, O. D.; Romanova, M. M.; Lovelace, R. V. E.

2014-09-01

We investigate the propagation of magnetized, isolated old neutron stars through the interstellar medium. We performed axisymmetric, non-relativistic magnetohydrodynamic simulations of the supersonic motion of neutron star with dipole magnetic field aligned with its velocity through the interstellar medium (ISM). We consider two cases: (1) where the accretion radius is larger than Alfvén radius, i.e. Racc>>RA and gravitational focusing is important; and (2) where Racc<star interacts with the ISM as a “georotator”, without significant gravitational focusing. In the first case we observe Bondi-Hoyle accretion onto an isolated magnetized neutron star. In the second case magnetic field lines are stretched downwind from the star and form a hollow elongated magnetotail. Reconnection of the magnetic field is observed in the tail which may lead to acceleration of particles.

Neutron-capture Nucleosynthesis in the First Stars

NASA Astrophysics Data System (ADS)

Roederer, Ian U.; Preston, George W.; Thompson, Ian B.; Shectman, Stephen A.; Sneden, Christopher

2014-04-01

Recent studies suggest that metal-poor stars enhanced in carbon but containing low levels of neutron-capture elements may have been among the first to incorporate the nucleosynthesis products of the first generation of stars. We have observed 16 stars with enhanced carbon or nitrogen using the MIKE Spectrograph on the Magellan Telescopes at Las Campanas Observatory and the Tull Spectrograph on the Smith Telescope at McDonald Observatory. We present radial velocities, stellar parameters, and detailed abundance patterns for these stars. Strontium, yttrium, zirconium, barium, europium, ytterbium, and other heavy elements are detected. In four stars, these heavy elements appear to have originated in some form of r-process nucleosynthesis. In one star, a partial s-process origin is possible. The origin of the heavy elements in the rest of the sample cannot be determined unambiguously. The presence of elements heavier than the iron group offers further evidence that zero-metallicity rapidly rotating massive stars and pair instability supernovae did not contribute substantial amounts of neutron-capture elements to the regions where the stars in our sample formed. If the carbon- or nitrogen-enhanced metal-poor stars with low levels of neutron-capture elements were enriched by products of zero-metallicity supernovae only, then the presence of these heavy elements indicates that at least one form of neutron-capture reaction operated in some of the first stars. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile, and The McDonald Observatory of The University of Texas at Austin.

Non-identical neutron star twins

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glendenning, Norman K.; Kettner, Christiane

1998-07-01

The work of J. A. Wheeler in the mid 1960's showed that forsmooth equations of state no stable stellar configurations with centraldensities above that corresponding to the limiting mass of 'neutronstars' (in the generic sense) were stable against acoustical vibrationalmodes. A perturbation would cause any such star to collapse to a blackhole or explode. Accordingly, there has been no reason to expect that astable degenerate family of stars with higher density than the knownwhite dwarfs and neutron stars might exist. We have found a class ofexceptions corresponding to certain equations of state that describe afirst order phase transition. We discussmore » how such a higher density familyof stars could be formed in nature, and how the promising new explorationof oscillations in the X-ray brightness of accreting neutron stars mightprovide a means of identifying them. Our proof of the possible existenceof a third family of degenerate stars is one of principle and rests ongeneral principles like causality, microstability of matter and GeneralRelativity.« less

HOW GALACTIC ENVIRONMENT REGULATES STAR FORMATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meidt, Sharon E.

2016-02-10

In a new simple model I reconcile two contradictory views on the factors that determine the rate at which molecular clouds form stars—internal structure versus external, environmental influences—providing a unified picture for the regulation of star formation in galaxies. In the presence of external pressure, the pressure gradient set up within a self-gravitating turbulent (isothermal) cloud leads to a non-uniform density distribution. Thus the local environment of a cloud influences its internal structure. In the simple equilibrium model, the fraction of gas at high density in the cloud interior is determined simply by the cloud surface density, which is itselfmore » inherited from the pressure in the immediate surroundings. This idea is tested using measurements of the properties of local clouds, which are found to show remarkable agreement with the simple equilibrium model. The model also naturally predicts the star formation relation observed on cloud scales and at the same time provides a mapping between this relation and the closer-to-linear molecular star formation relation measured on larger scales in galaxies. The key is that pressure regulates not only the molecular content of the ISM but also the cloud surface density. I provide a straightforward prescription for the pressure regulation of star formation that can be directly implemented in numerical models. Predictions for the dense gas fraction and star formation efficiency measured on large-scales within galaxies are also presented, establishing the basis for a new picture of star formation regulated by galactic environment.« less

Colliding Neutron Stars as the Source of Heavy Elements

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-09-01

Where do the heavy elements the chemical elements beyond iron in our universe come from? One of the primary candidate sources is the merger of two neutron stars, but recent observations have cast doubt on this model. Can neutron-star mergers really be responsible?Elements from Collisions?Periodic table showing the origin of each chemical element. Those produced by the r-process are shaded orange and attributed to supernovae in this image; though supernovae are one proposed source of r-process elements, an alternative source is the merger of two neutron stars. [Cmglee]When a binary-neutron-star system inspirals and the two neutron stars smash into each other, a shower of neutrons are released. These neutrons are thought to bombard the surrounding atoms, rapidly producing heavy elements in what is known as r-process nucleosynthesis.So could these mergers be responsible for producing the majority of the universes heavy r-process elements? Proponents of this model argue that its supported by observations. The overall amount of heavy r-process material in the Milky Way, for instance, is consistent with the expected ejection amounts from mergers, based both on predicted merger rates for neutron stars in the galaxy, and on the observed rates of soft gamma-ray bursts (which are thought to accompany double-neutron-star mergers).Challenges from Ultra-Faint DwarfsRecently, however, r-process elements have been observed in ultra-faint dwarf satellite galaxies. This discovery raises two major challenges to the merger model for heavy-element production:When neutron stars are born during a core-collapse supernova, mass is ejected, providing the stars with asymmetric natal kicks. During the second collapse in a double-neutron-star binary, wouldnt the kick exceed the low escape velocity of an ultra-faint dwarf, ejecting the binary before it could merge and enrich the galaxy?Ultra-faint dwarfs have very old stellar populations and the observation of r-process elements in these stars

Interstellar Medium, Young Stars, and Astrometric Binaries in Galactic Archaeology Spectroscopic Surveys

NASA Astrophysics Data System (ADS)

Zwitter, T.; Kos, J.; Žerjal, M.; Traven, G.

2016-10-01

Current ongoing stellar spectroscopic surveys (RAVE, GALAH, Gaia-ESO, LAMOST, APOGEE, Gaia) are mostly devoted to studying Galactic archaeology and the structure of the Galaxy. But they allow also for important auxiliary science: (i) the Galactic interstellar medium can be studied in four dimensions (position in space plus radial velocity) through weak but numerous diffuse interstellar bands and atomic absorptions seen in spectra of background stars, (ii) emission spectra which are quite frequent even in field stars can serve as a good indicator of their youth, pointing e.g. to stars recently ejected from young stellar environments, (iii) an astrometric solution of the photocenter of a binary to be obtained by Gaia can yield accurate masses when joined by spectroscopic information obtained serendipitously during a survey. These points are illustrated by first results from the first three surveys mentioned above. These hint at the near future: spectroscopic studies of the dynamics of the interstellar medium can identify and quantify Galactic fountains which may sustain star formation in the disk by entraining fresh gas from the halo; RAVE already provided a list of ˜ 14,000 field stars with chromospheric emission in Ca II lines, to be supplemented by many more observations by Gaia in the same band, and by GALAH and Gaia-ESO observations of Balmer lines; several millions of astrometric binaries with periods up to a few years which are being observed by Gaia can yield accurate masses when supplemented with measurements from only a few high-quality ground based spectra.

Westerlund 1 is a Galactic Treasure Chest: The Wolf-Rayet Stars

NASA Astrophysics Data System (ADS)

Rosslowe, C. K.; Crowther, P. A.

2015-01-01

The Westerlund 1 Galactic cluster hosts an eclectic mix of coeval massive stars. At a modest distance of 4-5 kpc, it offers a unique opportunity to study the resolved stellar content of a young (~5 Myr) high mass (5.104 M ⊙) star cluster. With the aim of testing single-star evolutionary predictions, and revealing any signatures of binary evolution, we discuss on-going analyses of NTT/SOFI near-IR spectroscopy of Wolf-Rayet stars in Westerlund 1. We find that late WN stars are H-poor compared to their counterparts in the Milky Way field, and nearly all are less luminous than predicted by single-star Geneva isochrones at the age of Westerlund 1.

SUPERNOVAE, NEUTRON STARS, AND TWO KINDS OF NEUTRINO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chiu, H.Y.

1962-08-15

The role of neutrinos in the core of a star that has undergone a supernova explosion is discussed. The existence of neutron stars, the Schwarzchild singularity in general relativity, and the meaning of conservation of baryons in the neighborhood of a Schwarzchild singularity are also considered. The problem of detection of neutron stars is discussed. It is concluded that neutron stars are the most plausible alternative for the remnant of the core of a supernova. The neutrino emission processes are divided into two groups: the neutrino associated with the meson (mu) and the production of electron neutrinos. (C.E.S.)

The unusual gamma-ray burst GRB 101225A explained as a minor body falling onto a neutron star.

PubMed

Campana, S; Lodato, G; D'Avanzo, P; Panagia, N; Rossi, E M; Della Valle, M; Tagliaferri, G; Antonelli, L A; Covino, S; Ghirlanda, G; Ghisellini, G; Melandri, A; Pian, E; Salvaterra, R; Cusumano, G; D'Elia, V; Fugazza, D; Palazzi, E; Sbarufatti, B; Vergani, S D

2011-11-30

The tidal disruption of a solar-mass star around a supermassive black hole has been extensively studied analytically and numerically. In these events, the star develops into an elongated banana-shaped structure. After completing an eccentric orbit, the bound debris falls into the black hole, forming an accretion disk and emitting radiation. The same process may occur on planetary scales if a minor body passes too close to its star. In the Solar System, comets fall directly into our Sun or onto planets. If the star is a compact object, the minor body can become tidally disrupted. Indeed, one of the first mechanisms invoked to produce strong gamma-ray emission involved accretion of comets onto neutron stars in our Galaxy. Here we report that the peculiarities of the 'Christmas' gamma-ray burst (GRB 101225A) can be explained by a tidal disruption event of a minor body around an isolated Galactic neutron star. This would indicate either that minor bodies can be captured by compact stellar remnants more frequently than occurs in the Solar System or that minor-body formation is relatively easy around millisecond radio pulsars. A peculiar supernova associated with a gamma-ray burst provides an alternative explanation.

Gravitational-Wave Luminosity of Binary Neutron Stars Mergers

NASA Astrophysics Data System (ADS)

Zappa, Francesco; Bernuzzi, Sebastiano; Radice, David; Perego, Albino; Dietrich, Tim

2018-03-01

We study the gravitational-wave peak luminosity and radiated energy of quasicircular neutron star mergers using a large sample of numerical relativity simulations with different binary parameters and input physics. The peak luminosity for all the binaries can be described in terms of the mass ratio and of the leading-order post-Newtonian tidal parameter solely. The mergers resulting in a prompt collapse to black hole have the largest peak luminosities. However, the largest amount of energy per unit mass is radiated by mergers that produce a hypermassive neutron star or a massive neutron star remnant. We quantify the gravitational-wave luminosity of binary neutron star merger events, and set upper limits on the radiated energy and the remnant angular momentum from these events. We find that there is an empirical universal relation connecting the total gravitational radiation and the angular momentum of the remnant. Our results constrain the final spin of the remnant black hole and also indicate that stable neutron star remnant forms with super-Keplerian angular momentum.

Gravitational-Wave Luminosity of Binary Neutron Stars Mergers.

PubMed

Zappa, Francesco; Bernuzzi, Sebastiano; Radice, David; Perego, Albino; Dietrich, Tim

2018-03-16

We study the gravitational-wave peak luminosity and radiated energy of quasicircular neutron star mergers using a large sample of numerical relativity simulations with different binary parameters and input physics. The peak luminosity for all the binaries can be described in terms of the mass ratio and of the leading-order post-Newtonian tidal parameter solely. The mergers resulting in a prompt collapse to black hole have the largest peak luminosities. However, the largest amount of energy per unit mass is radiated by mergers that produce a hypermassive neutron star or a massive neutron star remnant. We quantify the gravitational-wave luminosity of binary neutron star merger events, and set upper limits on the radiated energy and the remnant angular momentum from these events. We find that there is an empirical universal relation connecting the total gravitational radiation and the angular momentum of the remnant. Our results constrain the final spin of the remnant black hole and also indicate that stable neutron star remnant forms with super-Keplerian angular momentum.

Star formation induced by cloud-cloud collisions and galactic giant molecular cloud evolution

NASA Astrophysics Data System (ADS)

Kobayashi, Masato I. N.; Kobayashi, Hiroshi; Inutsuka, Shu-ichiro; Fukui, Yasuo

2018-05-01

Recent millimeter/submillimeter observations towards nearby galaxies have started to map the whole disk and to identify giant molecular clouds (GMCs) even in the regions between galactic spiral structures. Observed variations of GMC mass functions in different galactic environments indicates that massive GMCs preferentially reside along galactic spiral structures whereas inter-arm regions have many small GMCs. Based on the phase transition dynamics from magnetized warm neutral medium to molecular clouds, Kobayashi et al. (2017, ApJ, 836, 175) proposes a semi-analytical evolutionary description for GMC mass functions including a cloud-cloud collision (CCC) process. Their results show that CCC is less dominant in shaping the mass function of GMCs than the accretion of dense H I gas driven by the propagation of supersonic shock waves. However, their formulation does not take into account the possible enhancement of star formation by CCC. Millimeter/submillimeter observations within the Milky Way indicate the importance of CCC in the formation of star clusters and massive stars. In this article, we reformulate the time-evolution equation largely modified from Kobayashi et al. (2017, ApJ, 836, 175) so that we additionally compute star formation subsequently taking place in CCC clouds. Our results suggest that, although CCC events between smaller clouds are more frequent than the ones between massive GMCs, CCC-driven star formation is mostly driven by massive GMCs ≳ 10^{5.5} M_{⊙} (where M⊙ is the solar mass). The resultant cumulative CCC-driven star formation may amount to a few 10 percent of the total star formation in the Milky Way and nearby galaxies.

A Panoramic View of Star Formation in Milky Way: Recent Results from Galactic Plane FIR/Sub-mm Surveys

NASA Astrophysics Data System (ADS)

Elia, Davide

2017-11-01

The star formation process involves a continuous gas flow from galactic (kpc) down to stellar (AU) scales. While targeted observations of single star forming sources are needed to understand the steps of this process with increasing detail, large unbiased Galactic plane surveys permit to reconstruct the map of star forming sites across the Milky Way, considered as an unique star formation engine. On the one hand, such surveys provide the community with a huge number of candidate targets for future follow-up observations with state-of-the-art telescope facilities, on the other hand they can provide reliable estimates of global parameters, such as Galactic star formation efficiency and rate, through which it is possible to establish comparisons with other galaxies. In this talk I will review the main results of recent FIR/sub-mm continuum emission Galactic surveys, with special attention to the Hi-GAL Herschel project, having the advantage (but also the complication) of being a multi-wavelength survey covering the spectral range in which the cold interstellar dust is expected to emit. The subsequent VIALACTEA project represents an articulate effort to combine Hi-GAL with other continuum and line surveys to refine the census of star forming clumps in the Galactic plane, and to use it to describe the Milky Way as a whole. Interpretation limitations imposed by the loss of detail with increasing distance are also discussed.

Thermal states of neutron stars with a consistent model of interior

NASA Astrophysics Data System (ADS)

Fortin, M.; Taranto, G.; Burgio, G. F.; Haensel, P.; Schulze, H.-J.; Zdunik, J. L.

2018-04-01

We model the thermal states of both isolated neutron stars and accreting neutron stars in X-ray transients in quiescence and confront them with observations. We use an equation of state calculated using realistic two-body and three-body nucleon interactions, and superfluid nucleon gaps obtained using the same microscopic approach in the BCS approximation. Consistency with low-luminosity accreting neutron stars is obtained, as the direct Urca process is operating in neutron stars with mass larger than 1.1 M⊙ for the employed equation of state. In addition, proton superfluidity and sufficiently weak neutron superfluidity, obtained using a scaling factor for the gaps, are necessary to explain the cooling of middle-aged neutron stars and to obtain a realistic distribution of neutron star masses.

Cyclotron Lines in Accreting Neutron Star Spectra

NASA Astrophysics Data System (ADS)

Wilms, Jörn; Schönherr, Gabriele; Schmid, Julia; Dauser, Thomas; Kreykenbohm, Ingo

2009-05-01

Cyclotron lines are formed through transitions of electrons between discrete Landau levels in the accretion columns of accreting neutron stars with strong (1012 G) magnetic fields. We summarize recent results on the formation of the spectral continuum of such systems, describe recent advances in the modeling of the lines based on a modification of the commonly used Monte Carlo approach, and discuss new results on the dependence of the measured cyclotron line energy from the luminosity of transient neutron star systems. Finally, we show that Simbol-X will be ideally suited to build and improve the observational database of accreting and strongly magnetized neutron stars.

Anisotropic neutron stars in R2 gravity

NASA Astrophysics Data System (ADS)

Folomeev, Vladimir

2018-06-01

We consider static neutron stars within the framework of R2 gravity. The neutron fluid is described by three different types of realistic equations of state (soft, moderately stiff, and stiff). Using the observational data on the neutron star mass-radius relation, it is demonstrated that the characteristics of the objects supported by the isotropic fluid agree with the observations only if one uses the soft equation of state. We show that the inclusion of the fluid anisotropy enables one also to employ more stiff equations of state to model configurations that will satisfy the observational constraints sufficiently. Also, using the standard thin accretion disk model, we demonstrate potentially observable differences, which allow us to distinguish the neutron stars constructed within the modified gravity framework from those described in Einstein's general relativity.

GOSSS-DR1: The First Data Release of the Galactic O-star Spectroscopic Survey

NASA Astrophysics Data System (ADS)

Sota, Alfredo; Maíz Apellániz, Jesús; Barbá, Rodolfo H.; Walborn, Nolan R.; Alfaro, Emilio J.; Gamen, Roberto C.; Morrell, Nidia I.; Arias, Julia I.; Gallego Calvente, A. T.

2013-06-01

Coinciding with this meeting, we are publishing the first data release of GOSSS. This release contains [a] revised spectral classifications and [b] blue-violet R~2500 spectra in FITS format for ~400 Galactic O stars, including all brighter than B=8. DR1 (and future releases) will take place through GOSC, the Galactic O-Star Catalog (http://gosc.iaa.es), which will be updated for the occasion. Since 2011 GOSC runs on a MySQL database and allows for queries based on coordinates, spectral class, photometry, and other parameters. Future data releases will include the rest of the stars observed in GOSSS (currently 1521 with ~1000 more planned in the next two years).

The black hole at the Galactic Center: observations and models in a nutshell

NASA Astrophysics Data System (ADS)

Zakharov, Alexander

2017-12-01

The Galactic Center (Sgr A*) is a peculiar place in our Galaxy (Milky Way). Our Solar system is located at a distance around 8 kpc from the Galactic Center (GC). There were a number of different including exotic ones such as boson stars, fermion balls, neutrino balls, a cluster of neutron stars. Some of these models are significantly constrained with consequent observations and now supermassive black hole with mass around 4 × 106 M ⊙ is the preferable model for GC. Moreover, one can test alternative theories of gravity with observations of bright stars near the Galactic Center and and observations of bright structures near the black hole at the Galactic Center to reconstruct shadow structure around the black hole with current and future observational VLBI facilities such as the Event Horizon Telescope. In particular, we got a graviton mass constraint which is comparable and consistent with constraints obtained recently by the LIGO-Virgo collaboration.

R-mode constraints from neutron star equation of state

NASA Astrophysics Data System (ADS)

Papazoglou, M. C.; Moustakidis, C. C.

2016-03-01

The gravitational radiation has been proposed a long time before, as an explanation for the observed relatively low spin frequencies of young neutron stars and of accreting neutron stars in low-mass X-ray binaries as well. In the present work we studied the effects of the neutron star equation of state on the r-mode instability window of rotating neutron stars. Firstly, we employed a set of analytical solution of the Tolman-Oppenheimer-Volkoff equations with special emphasis on the Tolman VII solution. In particular, we tried to clarify the effects of the bulk neutron star properties (mass, radius, density distribution, crust size and elasticity) on the r-mode instability window. We found that the critical angular velocity \\varOmegac depends mainly on the neutron star radius. The effects of the gravitational mass and the mass distribution are almost negligible. Secondly, we studied the effect of the elasticity of the crust, via to the slippage factor S and also the effect of the nuclear equation of state, via the slope parameter L, on the instability window. We found that the crust effects are more pronounced, compared to those originated from the equation of state. Moreover, we proposed simple analytical expressions which relate the macroscopic quantity \\varOmegac to the radius, the parameter L and the factor {S}. We also investigated the possibility to measure the radius of a neutron star and the factor {S} with the help of accurate measures of \\varOmegac and the neutron star temperature. Finally, we studied the effects of the mutual friction on the instability window and discussed the results in comparison with previous similar studies.

Flux-limited sample of Galactic carbon stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Claussen, M.J.; Kleinmann, S.G.; Joyce, R.R.

Published observational data (including IRAS observations) for a flux-limited sample of 215 Galactic carbon stars (CSs) selected from the 2-micron sky survey of Neugebauer and Leighton (1969) are compiled in extensive tables and graphs and analyzed statistically. The sample is found to penetrate a volume of radius 1.5 kpc, and the local CS space density and surface density are calculated as log rho0 (per cu kpc) = 2.0 + or - 0.4 and log N (per sq kpc) = 1.6 + or - 0.2, respectively. The total Galactic mass-return rate from these CSs is estimated as 0.013 solar mass/yr, implyingmore » a time scale of 0.1-1 Myr for the CS evolutionary phase and a mass of 1.2-1.6 solar mass for the (probably F-type) main-seqence progenitors of CSs. 81 references.« less

MODEL ATMOSPHERES FOR X-RAY BURSTING NEUTRON STARS

DOE PAGES

Medin, Zachary James; Steinkirch, Marina von; Calder, Alan C.; ...

2016-11-21

The hydrogen and helium accreted by X-ray bursting neutron stars is periodically consumed in runaway thermonuclear reactions that cause the entire surface to glow brightly in X-rays for a few seconds. With models of the emission, the mass and radius of the neutron star can be inferred from the observations. By simultaneously probing neutron star masses and radii, X-ray bursts (XRBs) are one of the strongest diagnostics of the nature of matter at extremely high densities. Accurate determinations of these parameters are difficult, however, due to the highly non-ideal nature of the atmospheres where XRBs occur. Also, observations from X-raymore » telescopes such as RXTE and NuStar can potentially place strong constraints on nuclear matter once uncertainties in atmosphere models have been reduced. Lastly, here we discuss current progress on modeling atmospheres of X-ray bursting neutron stars and some of the challenges still to be overcome.« less

Physics in Strong Magnetic Fields Near Neutron Stars.

ERIC Educational Resources Information Center

Harding, Alice K.

1991-01-01

Discussed are the behaviors of particles and energies in the magnetic fields of neutron stars. Different types of possible research using neutron stars as a laboratory for the study of strong magnetic fields are proposed. (CW)

Effect of non-stationary accretion on spectral state transitions: An example of a persistent neutron star LMXB 4U1636–536

NASA Astrophysics Data System (ADS)

Zhang, Hui; Yu, Wen-Fei

2018-03-01

Observations of black hole and neutron star X-ray binaries show that the luminosity of the hard-to-soft state transition is usually higher than that of the soft-to-hard state transition, indicating additional parameters other than mass accretion rate are required to interpret spectral state transitions. It has been found in some individual black hole or neutron star soft X-ray transients that the luminosity corresponding to the hard-to-soft state transition is positively correlated with the peak luminosity of the following soft state. In this work, we report the discovery of the same correlation in the single persistent neutron star low mass X-ray binary (LMXB) 4U 1636–536 based on data from the All Sky Monitor (ASM) on board RXTE, the Gas Slit Camera (GSC) on board MAXI and the Burst Alert Telescope (BAT) on board Swift. We also found such a positive correlation holds in this persistent neutron star LMXB in a luminosity range spanning about a factor of four. Our results indicate that non-stationary accretion also plays an important role in driving X-ray spectral state transitions in persistent accreting systems with small accretion flares, which is much less dramatic compared with the bright outbursts seen in many Galactic LMXB transients.

The Sixth Catalogue of galactic Wolf-Rayet stars, their past and present

NASA Technical Reports Server (NTRS)

Van Der Hucht, K. A.; Conti, P. S.; Lundstrom, I.; Stenholm, B.

1981-01-01

This paper presents the Sixth Catalogue of galactic Wolf-Rayet stars (Pop. I), a short history on the five earlier WR catalogues, improved spectral classification, finding charts, a discussion on related objects, and a review of the current status of Wolf-Rayet star research. The appendix presents a bibliography on most of the Wolf-Rayet literature published since 1867.

Advanced LIGO constraints on neutron star mergers and r-process sites

DOE PAGES

Côté, Benoit; Belczynski, Krzysztof; Fryer, Chris L.; ...

2017-02-20

The role of compact binary mergers as the main production site of r-process elements is investigated by combining stellar abundances of Eu observed in the Milky Way, galactic chemical evolution (GCE) simulations, and binary population synthesis models, and gravitational wave measurements from Advanced LIGO. We compiled and reviewed seven recent GCE studies to extract the frequency of neutron star–neutron star (NS–NS) mergers that is needed in order to reproduce the observed [Eu/Fe] versus [Fe/H] relationship. We used our simple chemical evolution code to explore the impact of different analytical delay-time distribution functions for NS–NS mergers. We then combined our metallicity-dependent population synthesis models with our chemical evolution code to bring their predictions, for both NS–NS mergers and black hole–neutron star mergers, into a GCE context. Finally, we convolved our results with the cosmic star formation history to provide a direct comparison with current and upcoming Advanced LIGO measurements. When assuming that NS–NS mergers are the exclusive r-process sites, and that the ejected r-process mass per merger event is 0.01 Mmore » $${}_{\\odot }$$, the number of NS–NS mergers needed in GCE studies is about 10 times larger than what is predicted by standard population synthesis models. Here, these two distinct fields can only be consistent with each other when assuming optimistic rates, massive NS–NS merger ejecta, and low Fe yields for massive stars. For now, population synthesis models and GCE simulations are in agreement with the current upper limit (O1) established by Advanced LIGO during their first run of observations. Upcoming measurements will provide an important constraint on the actual local NS–NS merger rate, will provide valuable insights on the plausibility of the GCE requirement, and will help to define whether or not compact binary mergers can be the dominant source of r-process elements in the universe.« less

Evolution of Supernova Remnants Near the Galactic Center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yalinewich, A.; Piran, T.; Sari, R.

Supernovae near the Galactic center (GC) evolve differently from regular Galactic supernovae. This is mainly due to the environment into which the supernova remnants (SNRs) propagate. SNRs near the GC propagate into a wind swept environment with a velocity directed away from the GC, and a graded density profile. This causes these SNRs to be non-spherical, and to evolve faster than their Galactic counterparts. We develop an analytic theory for the evolution of explosions within a stellar wind, and verify it using a hydrodynamic code. We show that such explosions can evolve in one of three possible morphologies. Using thesemore » results we discuss the association between the two SNRs (SGR East and SGR A’s bipolar radio/X-ray lobes) and the two neutron stars (the Cannonball and SGR J1745-2900) near the GC. We show that, given the morphologies of the SNR and positions of the neutron stars, the only possible association is between SGR A’s bipolar radio/X-ray lobes and SGR J1745-2900. If a compact object was created in the explosion of SGR East, it remains undetected, and the SNR of the supernova that created the Cannonball has already disappeared.« less

Quasiparticle Interactions in Neutron Matter for Applications in Neutron Stars

NASA Technical Reports Server (NTRS)

Wambach, J.; Anisworth, T. L.; Pines, D.

1993-01-01

A microscopic model for the quaisiparticle interaction in neutron matter is presented. Both particle-particle (pp) and particle-hole (ph) correlation are are included. The pp correlations are treated in semi-empirical way, while ph correlations are incorporated by solving coupled two-body equations for the particle hole interaction and the scattering amplitude on the Fermi sphere. The resulting integral equations self-consistently sum the ph reducible diagrams. Antisymmetry is kept at all stages and hence the forward-scattering sum rules are obeyed. Results for Landau parameters and transport coefficients in a density regime representing the crust of a neutron star are presented. We also estimate the S-1 gap parameter for neutron superfluidity and comment briefly on neutron-star implications.

Quasiparticle Interactions in Neutron Matter for Applications in Neutron Stars

NASA Technical Reports Server (NTRS)

Wambach, J; Ainsworth, T. L.; Pines, D.

1993-01-01

A microscopic model for the quasiparticle interaction in neutron matter is presented. Both-particle (pp) and particle-hole (ph) correlations are included. The pp correlations are treated in semi-empirical way, while ph correlations are incorporated by solving coupled two-body equations for particle-hole interaction and the scattering amplitude of the Fermi sphere. The resulting integral equations self-consistently sum the ph reducible diagrams. Antisymmetry is kept at all stages and hence the forward-scattering sum rules for the scattering amplitude are obeyed. Results for Landau parameters and transport coefficients in a density regime representing the crust of a neutron star are presented. We also estimate the (1)S(sub 0) gap parameter for neutron superfluidity and comment briefly on neutron-star implications.

NeutronSTARS: A segmented neutron and charged particle detector for low-energy reaction studies

DOE PAGES

Akindele, O. A.; Casperson, R. J.; Wang, B. S.; ...

2017-08-10

NeutronSTARS (Neutron-S ilicon T elescope A rray for R eaction S tudies) consists of 2.2-tons of gadolinium-doped liquid scintillator for neutron detection and large area silicon detectors for charged particle identification. This detector array is intended for low-energy-nuclear-reaction measurements that result in the emission of neutrons such as and fission. This paper describes the NeutronSTARS experimental setup, calibration, and the array’s response to neutral and charged particles.

Gamma-Ray Bursts from Neutron Star Kicks

NASA Astrophysics Data System (ADS)

Huang, Y. F.; Dai, Z. G.; Lu, T.; Cheng, K. S.; Wu, X. F.

2003-09-01

The idea that gamma-ray bursts might be a phenomenon associated with neutron star kicks was first proposed by Dar & Plaga. Here we study this mechanism in more detail and point out that the neutron star should be a high-speed one (with proper motion larger than ~1000 km s-1). It is shown that the model agrees well with observations in many aspects, such as the energetics, the event rate, the collimation, the bimodal distribution of durations, the narrowly clustered intrinsic energy, and the association of gamma-ray bursts with supernovae and star-forming regions. We also discuss the implications of this model on the neutron star kick mechanism and suggest that the high kick speed was probably acquired as the result of the electromagnetic rocket effect of a millisecond magnetar with an off-centered magnetic dipole.

Probing thermonuclear burning on accreting neutron stars

NASA Astrophysics Data System (ADS)

Keek, L.

2008-12-01

Neutron stars are the most compact stars that can be directly observed, which makes them ideal laboratories to study physics at extreme densities. Neutron stars in low-mass X-ray binaries accrete hydrogen and helium from a lower-mass companion star through Roche lobe overflow. This matter undergoes thermonuclear burning in the neutron star envelope, creating carbon and heavier elements. The fusion process may proceed in an unstable manner, resulting in a thermonuclear runaway. Within one second the entire surface is burned, which is observable as a sharp rise in the emitted X-ray flux: a type I X-ray burst. Afterwards the neutron star surface cools down on a timescale of ten to one hundred seconds. During these bursts the surface of an accreting neutron star can be observed directly, which makes them instrumental for studying this type of stars. We have studied rare kinds of X-ray bursts. One such rare burst is the superburst, which lasts a thousand times longer than an ordinary burst. Superbursts are thought to result from the explosive burning of a thick carbon layer, which lies deeper inside the neutron star, close to a layer known as the crust. A prerequisite for the occurrence of a superburst is a high enough temperature, which is set by the temperature of the crust and the heat conductivity of the envelope. The latter is lowered by the presence of heavy elements that are produced during normal X-ray bursts. Using a large set of observations from the Wide Field Camera's onboard the BeppoSAX satellite, we find that, at high accretion rate, sources which do not exhibit normal bursts likely have a longer superburst recurrence time, than the observed superburst recurrence time of one burster. We analyze in detail the first superburst from a transient source, which went into outburst only 55 days before the superburst. Recent models of the neutron star crust predict that this is too small a time to heat the crust sufficiently for superburst ignition, indicating

Neutron stars structure in the context of massive gravity

NASA Astrophysics Data System (ADS)

Hendi, S. H.; Bordbar, G. H.; Eslam Panah, B.; Panahiyan, S.

2017-07-01

Motivated by the recent interests in spin-2 massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in 4 and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV18 potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

Accreting neutron stars, black holes, and degenerate dwarf stars.

PubMed

Pines, D

1980-02-08

During the past 8 years, extended temporal and broadband spectroscopic studies carried out by x-ray astronomical satellites have led to the identification of specific compact x-ray sources as accreting neutron stars, black holes, and degenerate dwarf stars in close binary systems. Such sources provide a unique opportunity to study matter under extreme conditions not accessible in the terrestrial laboratory. Quantitative theoretical models have been developed which demonstrate that detailed studies of these sources will lead to a greatly increased understanding of dense and superdense hadron matter, hadron superfluidity, high-temperature plasma in superstrong magnetic fields, and physical processes in strong gravitational fields. Through a combination of theory and observation such studies will make possible the determination of the mass, radius, magnetic field, and structure of neutron stars and degenerate dwarf stars and the identification of further candidate black holes, and will contribute appreciably to our understanding of the physics of accretion by compact astronomical objects.

Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, volume 73

NASA Technical Reports Server (NTRS)

Haas, Michael R. (Editor); Davidson, Jacqueline A. (Editor); Erickson, Edwin F. (Editor)

1995-01-01

This symposium was organized to review the science related to NASA's Airborne Astronomy Program on the occasion of the twentieth anniversary of the Kuiper Airborne Observatory (KAO). The theme selected, 'The Galactic Ecosystem: From Gas to Stars to Dust,' was considered to capture the underlying commonality of much of the research discussed. The 8 sessions were as follows: The Interstellar Medium; The Life Cycle of the ISM in Other Galaxies; Star and Planetary System Formation; Our Planetary System: The Solar System; The Enrichment of the Interstellar Medium; The Galactic Center: A Unique Region of the Galactic Ecosystem; Instrumentation for Airborne Astronomy; KAO History and Education; and Missions and the Future of Infrared Astronomy.

Exploring the total Galactic extinction with SDSS BHB stars

NASA Astrophysics Data System (ADS)

Tian, Hai-Jun; Liu, Chao; Hu, Jing-Yao; Xu, Yang; Chen, Xue-Lei

2014-01-01

Aims: We used 12 530 photometrically-selected blue horizontal branch (BHB) stars from the Sloan Digital Sky Survey (SDSS) to estimate the total extinction of the Milky Way at the high Galactic latitudes, RV and AV in each line of sight. Methods: A Bayesian method was developed to estimate the reddening values in the given lines of sight. Based on the most likely values of reddening in multiple colors, we were able to derive the values of RV and AV. Results: We selected 94 zero-reddened BHB stars from seven globular clusters as the template. The reddening in the four SDSS colors for the northern Galactic cap were estimated by comparing the field BHB stars with the template stars. The accuracy of this estimation is around 0.01 mag for most lines of sight. We also obtained ⟨ RV ⟩ to be around 2.40 ± 1.05 and AV map within an uncertainty of 0.1 mag. The results, including reddening values in the four SDSS colors, AV, and RV in each line of sight, are released on line. In this work, we employ an up-to-date parallel technique on GPU card to overcome time-consuming computations. We plan to release online the C++ CUDA code used for this analysis. Conclusions: The extinction map derived from BHB stars is highly consistent with that from Schlegel et al. (1998, ApJ, 500, 525). The derived RV is around 2.40 ± 1.05. The contamination probably makes the RV be larger. Tables 1-4 (excerpt) are available in electronic form at http://www.aanda.orgFull Table 4 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/561/A142

Star motion around rotating black hole in the Galactic Center in real time

NASA Astrophysics Data System (ADS)

Dokuchaev, Vyacheslav; Nazarova, Natalia

2017-12-01

The Event Horizon Telescope team intends by the 2020 to resolve the shadow of supermassive black hole SgrA* in the Galactic Center. It would be the first attempt for direct identification of the enigmatic black hole. In other words, it would be the first experimental verification of the General Relativity in the strong field limit. There is a chance to find a star moving on the relativistic orbit close to this black hole. We present the animated numerical model of the gravitational lensing of a star (or any other lighting probe), moving around rotating Kerr black hole in the Galactic Center and viewed by the distant observer.

Chandra Finds Evidence for Swarm of Black Holes Near the Galactic Center

NASA Astrophysics Data System (ADS)

2005-01-01

A swarm of 10,000 or more black holes may be orbiting the Milky Way's supermassive black hole, according to new results from NASA's Chandra X-ray Observatory. This would represent the highest concentration of black holes anywhere in the Galaxy. These relatively small, stellar-mass black holes, along with neutron stars, appear to have migrated into the Galactic Center over the course of several billion years. Such a dense stellar graveyard has been predicted for years, and this represents the best evidence to date of its existence. The Chandra data may also help astronomers better understand how the supermassive black hole at the center of the Milky Way grows. The discovery was made as part of Chandra's ongoing program of monitoring the region around Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way. It was announced today by Michael Muno of the University of California, Los Angeles (UCLA) at a meeting of the American Astronomical Society in San Diego, CA. Animation: Sequence Showing Evidence of Black Hole Swarm in Context Animation: Sequence Showing Evidence of Black Hole Swarm in Context Among the thousands of X-ray sources detected within 70 light years of Sgr A*, Muno and his colleagues searched for those most likely to be active black holes and neutron stars by selecting only the brightest sources that also exhibited large variations in their X-ray output. These characteristics identify black holes and neutron stars that are in binary star systems and are pulling matter from nearby companion stars. Of the seven sources that met these criteria, four are within three light years of Sgr A*. "Although the region around Sgr A* is crowded with stars, we expected that there was only a 20 percent chance that we would find even one X-ray binary within a three-light-year radius," said Muno. "The observed high concentration of these sources implies that a huge number of black holes and neutron stars have gathered in the center of the

Documentation for the machine-readable version of the catalog of galactic O type stars

NASA Technical Reports Server (NTRS)

Warren, W. H., Jr.

1982-01-01

The Catalog of Galactic O-Type Stars (Garmany, Conti and Chiosi 1982), a compilation from the literature of all O-type stars for which spectral types, luminosity classes and UBV photometry exist, contains 765 stars, for each of which designation (HD, DM, etc.), spectral type, V, B-V, cluster membership, Galactic coordinates, and source references are given. Derived values of absolute visual and bolometric magnitudes, and distances are included. The source reference should be consulted for additional details concerning the derived quantities. This description of the machine-readable version of the catalog seeks to enable users to read and process the data with a minimum of guesswork. A copy of this document should be distributed with any machine readable version of the catalog.

The Magnetic Properties of Galactic OB Stars from the Magnetism in Massive Stars Project

NASA Astrophysics Data System (ADS)

Wade, Gregg A.; Grunhut, Jason; Petit, Veronique; Neiner, Coralie; Alecian, Evelyne; Landstreet, John; MiMeS Collaboration

2013-06-01

The Magnetism in Massive Stars (MiMeS) project represents the largest systematic survey of stellar magnetism ever undertaken. Comprising nearly 4500 high resolution polarised spectra of nearly 550 Galactic B and O-type stars, the MiMeS survey aims to address interesting and fundamental questions about the magnetism of hot, massive stars: How and when are massive star magnetic fields generated, and how do they evolve throughout stellar evolution? How do magnetic fields couple to and interact with the powerful winds of OB stars, and what are the consequences for the wind structure, momentum flux and energetics? What are the detailed physical mechanisms that lead to the anomalously slow rotation of many magnetic massive stars? What is the ultimate impact of stellar magnetic fields -- both direct and indirect -- on the evolution of massive stars? In this talk we report results from the analysis of the B-type stars observed within the MiMeS survey. The sample consists of over 450 stars ranging in spectral type from B9 to B0, and in evolutionary stage from the pre-main sequence to the post-main sequence. In addition to general statistical results concerning field incidence, strength and topology, we will elaborate our conclusions for subsamples of special interest, including the Herbig and classical Be stars, pulsating B stars and chemically peculiar B stars.

WEIGHING THE GALACTIC DARK MATTER HALO: A LOWER MASS LIMIT FROM THE FASTEST HALO STAR KNOWN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Przybilla, Norbert; Tillich, Alfred; Heber, Ulrich

2010-07-20

The mass of the Galactic dark matter halo is under vivid discussion. A recent study by Xue et al. revised the Galactic halo mass downward by a factor of {approx}2 relative to previous work, based on the line-of-sight velocity distribution of {approx}2400 blue horizontal-branch (BHB) halo stars. The observations were interpreted with a statistical approach using cosmological galaxy formation simulations, as only four of the six-dimensional phase-space coordinates were determined. Here we concentrate on a close investigation of the stars with the highest negative radial velocity from that sample. For one star, SDSSJ153935.67+023909.8 (J1539+0239 for short), we succeed in measuringmore » a significant proper motion, i.e., full phase-space information is obtained. We confirm the star to be a Population II BHB star from an independent quantitative analysis of the Sloan Digital Sky Survey (SDSS) spectrum-providing the first non-LTE (NLTE) study of any halo BHB star-and reconstruct its three-dimensional trajectory in the Galactic potential. J1539+0239 turns out to be the fastest halo star known to date, with a Galactic rest-frame velocity of 694{sup +300}{sub -221} km s{sup -1} (full uncertainty range from Monte Carlo error propagation) at its current position. The extreme kinematics of the star allows a significant lower limit to be put on the halo mass in order to keep it bound, of M {sub halo} {>=} 1.7{sup +2.3}{sub -1.1} x 10{sup 12} M{sub sun}. We conclude that the Xue et al. results tend to underestimate the true halo mass as their most likely mass value is consistent with our analysis only at a level of 4%. However, our result confirms other studies that make use of the full phase-space information.« less

Direct URCA process in neutron stars

NASA Technical Reports Server (NTRS)

Lattimer, James M.; Prakash, Madappa; Pethick, C. J.; Haensel, Pawel

1991-01-01

It is shown that the direct URCA process can occur in neutron stars if the proton concentration exceeds some critical value in the range 11-15 percent. The proton concentration, which is determined by the poorly known symmetry energy of matter above nuclear density, exceeds the critical value in many current calculations. If it occurs, the direct URCA process enhances neutrino emission and neutron star cooling rates by a large factor compared to any process considered previously.

A Statistical Study of the Mass Distribution of Neutron Stars

NASA Astrophysics Data System (ADS)

Cheng, Zheng; Zhang, Cheng-Min; Zhao, Yong-Heng; Wang, De-Hua; Pan, Yuan-Yue; Lei, Ya-Juan

2014-07-01

By reviewing the methods of mass measurements of neutron stars in four different kinds of systems, i.e., the high-mass X-ray binaries (HMXBs), low-mass X-ray binaries (LMXBs), double neutron star systems (DNSs) and neutron star-white dwarf (NS-WD) binary systems, we have collected the orbital parameters of 40 systems. By using the boot-strap method and the Monte-Carlo method, we have rebuilt the likelihood probability curves of the measured masses of 46 neutron stars. The statistical analysis of the simulation results shows that the masses of neutron stars in the X-ray neutron star systems and those in the radio pulsar systems exhibit different distributions. Besides, the Bayes statistics of these four different kind systems yields the most-probable probability density distributions of these four kind systems to be (1.340 ± 0.230)M8, (1, 505 ± 0.125)M8,(1.335 ± 0.055)M8 and (1.495 ± 0.225)M8, respectively. It is noteworthy that the masses of neutron stars in the HMXB and DNS systems are smaller than those in the other two kind systems by approximately 0.16M8. This result is consistent with the theoretical model of the pulsar to be accelerated to the millisecond order of magnitude via accretion of approximately 0.2M8. If the HMXBs and LMXBs are respectively taken to be the precursors of the BNS and NS-WD systems, then the influence of the accretion effect on the masses of neutron stars in the HMXB systems should be exceedingly small. Their mass distributions should be very close to the initial one during the formation of neutron stars. As for the LMXB and NS-WD systems, they should have already under- gone the process of suffcient accretion, hence there arises rather large deviation from the initial mass distribution.

Measuring neutron star tidal deformability with Advanced LIGO: black hole - neutron star binaries

NASA Astrophysics Data System (ADS)

Kumar, Prayush; Pürrer, Michael; Pfeiffer, Harald

2017-01-01

The pioneering observations of gravitational waves (GW) by Advanced LIGO have ushered us into an era of observational GW astrophysics. Compact binaries remain the primary target sources for GW observations, of which black hole - neutron star (BHNS) binaries form an important subset. GWs from coalescing BHNS systems carry signatures of the tidal distortion of the neutron star by its companion black hole during inspiral, as well as of its disruption close to merger. In this talk, I will discuss how well we can measure tidal effects from individual and populations of LIGO observations of disruptive BHNS mergers. I will also talk about how our measurements of non-tidal parameters can get affected by ignoring tidal effects in BHNS parameter estimation.

The Galactic evolution of phosphorus

NASA Astrophysics Data System (ADS)

Caffau, E.; Bonifacio, P.; Faraggiana, R.; Steffen, M.

2011-08-01

Context. As a galaxy evolves, its chemical composition changes and the abundance ratios of different elements are powerful probes of the underlying evolutionary processes. Phosphorous is an element whose evolution has remained quite elusive until now, because it is difficult to detect in cool stars. The infrared weak P i lines of the multiplet 1, at 1050-1082 nm, are the most reliable indicators of the presence of phosphorus. The availability of CRIRES at VLT has permitted access to this wavelength range in stellar spectra. Aims: We attempt to measure the phosphorus abundance of twenty cool stars in the Galactic disk. Methods: The spectra are analysed with one-dimensional model-atmospheres computed in local thermodynamic equilibrium (LTE). The line formation computations are performed assuming LTE. Results: The ratio of phosphorus to iron behaves similarly to sulphur, increasing towards lower metallicity stars. Its ratio with respect to sulphur is roughly constant and slightly larger than solar, [P/S] = 0.10 ± 0.10. Conclusions: We succeed in taking an important step towards the understanding of the chemical evolution of phosphorus in the Galaxy. However, the observed rise in the P/Fe abundance ratio is steeper than predicted by Galactic chemical evolution model developed by Kobayashi and collaborators. Phosphorus appears to evolve differently from the light odd-Z elements sodium and aluminium. The constant value of [P/S] with metallicity implies that P production is insensitive to the neutron excess, thus processes other than neutron captures operate. We suggest that proton captures on 30Si and α captures on 27Al are possibilities to investigate. We see no clear distinction between our results for stars with planets and stars without any detected planet. Based on observations obtained with the CRIRES spectrograph at ESO-VLT Antu 8.2 m telescope at Paranal, Programme 386.D-0130, P.I. E. Caffau.

The Star Formation Scenario in the Galactic Range from Ophiuchus to Chamaeleon

NASA Astrophysics Data System (ADS)

Sartori, Marília J.

2000-07-01

The molecular cloud complexes of Chamaeleon, Lupus and Ophiuchus, and the OB sub-groups of stars that form the Scorpius OB2 association are located at galactic longitudes in the interval 290° to 360°, all of them in a distance range from 100 to 200 pc. The distribution of known young stars in this region, both of low and of high mass, suggests that they belong to a single large structure. Moreover, a significant number of pre-main sequence (PMS) stars far from the star-forming clouds have been recently discovered. This scenario suggests that a global analysis of the star formation must be performed, especially of such nearby regions for which a large amount of data can be obtained. In order to test the models that intend to describe the history of star formation in these nearby star-forming regions, we collected information on the distribution of gas and dust and on the related young stellar populations. We mapped the molecular clouds of the complexes located in Chamaeleon, Lupus and Ophiuchus by means of an automatic method for star counting on plates of the Digitized Sky Survey. Another improvement with respect to the traditional star counts method is that we have adopted a relation between the extinction and the number of stars based on the predictions of the Galaxy's model by Ortiz & Lépine (1993, A&A 279, 90). Our maps confirm that there is an extended distribution of dust in the regions between the main clouds. We built a complete list of PMS and early-type stars from the literature, including all the available distance, radial velocity and proper motion data. We completed these data with our own determinations of proper motions of PMS stars, using positions obtained with the Valinhos Meridian Circle (IAG/USP, Brazil), photographic plates and public catalogs (Teixeira et al. 2000, A&A in press). Using these kinematical data and comparing the positions and spatial velocities of PMS stars to those of early-type stars, we verified that the kinematics of the

ON THE MASS DISTRIBUTION AND BIRTH MASSES OF NEUTRON STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oezel, Feryal; Psaltis, Dimitrios; Santos Villarreal, Antonio

We investigate the distribution of neutron star masses in different populations of binaries, employing Bayesian statistical techniques. In particular, we explore the differences in neutron star masses between sources that have experienced distinct evolutionary paths and accretion episodes. We find that the distribution of neutron star masses in non-recycled eclipsing high-mass binaries as well as of slow pulsars, which are all believed to be near their birth masses, has a mean of 1.28 M{sub Sun} and a dispersion of 0.24 M{sub Sun }. These values are consistent with expectations for neutron star formation in core-collapse supernovae. On the other hand,more » double neutron stars, which are also believed to be near their birth masses, have a much narrower mass distribution, peaking at 1.33 M{sub Sun }, but with a dispersion of only 0.05 M{sub Sun }. Such a small dispersion cannot easily be understood and perhaps points to a particular and rare formation channel. The mass distribution of neutron stars that have been recycled has a mean of 1.48 M{sub Sun} and a dispersion of 0.2 M{sub Sun }, consistent with the expectation that they have experienced extended mass accretion episodes. The fact that only a very small fraction of recycled neutron stars in the inferred distribution have masses that exceed {approx}2 M{sub Sun} suggests that only a few of these neutron stars cross the mass threshold to form low-mass black holes.« less

The Case of the Neutron Star With a Wayward Wake

NASA Astrophysics Data System (ADS)

2006-06-01

A long observation with NASA's Chandra X-ray Observatory has revealed important new details of a neutron star that is spewing out a wake of high-energy particles as it races through space. The deduced location of the neutron star on the edge of a supernova remnant, and the peculiar orientation of the neutron star wake, pose mysteries that remain unresolved. "Like a kite flying in the wind, the behavior of this neutron star and its wake tell us what sort of gas it must be plowing through," said Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., and lead author of a paper accepted to The Astrophysical Journal. "Yet we're still not sure how the neutron star got to its present location." Animation: Sequence of images of J0617 in IC 443 Animation: Sequence of images of J0617 in IC 443 The neutron star, known as CXOU J061705.3+222127, or J0617 for short, appears to lie near the outer edge of an expanding bubble of hot gas associated with the supernova remnant IC 443. Presumably, J0617 was created at the time of the supernova -- approximately 30,000 years ago -- and propelled away from the site of the explosion at about 500,000 miles per hour. However, the neutron star's wake is oriented almost perpendicularly to the direction expected if the neutron star were moving away from the center of the supernova remnant. This apparent misalignment had previously raised doubts about the association of the speeding neutron star with the supernova remnant. Gaensler and his colleagues provide strong evidence that J0617 was indeed born in the same explosion that created the supernova remnant. First, the shape of the neutron star's wake indicates it is moving a little faster than the speed of sound in Composite Images of SNR IC 443 Composite Images of SNR IC 443 the remnant's multimillion-degree gas. The velocity that one can then calculate from this conclusion closely matches the predicted pace of the neutron star. In contrast, if the neutron

Infrared Spectroscopy of Star Formation in Galactic and Extragalactic Regions

NASA Technical Reports Server (NTRS)

Smith, Howard A.; Hasan, Hashima (Technical Monitor)

2002-01-01

This report details work done in a project involving spectroscopic studies, including data analysis and modeling, of star-formation regions using an ensemble of archival space-based data including some from the Infrared Space Observatory's Long Wavelength Spectrometer and Short Wavelength Spectrometer, and other spectroscopic databases. We will include four kinds of regions: (1) disks around more evolved objects; (2) young, low or high mass pre-main sequence stars in star-formation regions; (3) star formation in external, bright IR (infrared) galaxies; and (4) the galactic center. During this period, work proceeded fully on track and on time. Details on workshops and conferences attended and research results are presented. A preprint article entitled 'The Far Infrared Lines of OH as Molecular Cloud Diagnostics' is included as an appendix.

Neutron stars: history of the magnetic field decay

NASA Astrophysics Data System (ADS)

Igoshev, Andrei P.; Kholtygin, Alexander F.

2013-03-01

Using the data of the ATNF pulsar catalog we study the relation connected the real age t of young neutron stars (NS) and their spin-down age τ. We suppose that this relation is independent from both initial period of the NS and its initial surface magnetic field, and that the laws of the surface magnetic field decay are similar for all NSs in the Milky Way. We further assume that the birth-rate of pulsars was constant during at least last 200 million years. With these assumptions we were able to restore the history of the magnetic field decay for the galactic NSs. We reconstruct the universal function f(t) = B(t)/B 0, where B 0 is the initial magnetic field and B(t) is the magnetic field of NS at the age t. The function f(t) can be fitted by a power law with power index α = -1.17.

An Integrated Picture of Star Formation, Metallicity Evolution, and Galactic Stellar Mass Assembly

NASA Astrophysics Data System (ADS)

Cowie, L. L.; Barger, A. J.

2008-10-01

We present an integrated study of star formation and galactic stellar mass assembly from z = 0.05 to 1.5 and galactic metallicity evolution from z = 0.05 to 0.9 using a very large and highly spectroscopically complete sample selected by rest-frame NIR bolometric flux in the GOODS-N. We assume a Salpeter IMF and fit Bruzual & Charlot models to compute the galactic stellar masses and extinctions. We determine the expected formed stellar mass density growth rates produced by star formation and compare them with the growth rates measured from the formed stellar mass functions by mass interval. We show that the growth rates match if the IMF is slightly increased from the Salpeter IMF at intermediate masses (~10 M⊙). We investigate the evolution of galaxy color, spectral type, and morphology with mass and redshift and the evolution of mass with environment. We find that applying extinction corrections is critical when analyzing galaxy colors; e.g., nearly all of the galaxies in the green valley are 24 μm sources, but after correcting for extinction, the bulk of the 24 μm sources lie in the blue cloud. We find an evolution of the metallicity-mass relation corresponding to a decrease of 0.21 +/- 0.03 dex between the local value and the value at z = 0.77 in the 1010-1011 M⊙ range. We use the metallicity evolution to estimate the gas mass of the galaxies, which we compare with the galactic stellar mass assembly and star formation histories. Overall, our measurements are consistent with a galaxy evolution process dominated by episodic bursts of star formation and where star formation in the most massive galaxies (gtrsim1011 M⊙) ceases at z < 1.5 because of gas starvation. Based in part on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA and was made possible by the generous financial support of the W. M. Keck Foundation.

EUV/soft x-ray spectra for low B neutron stars

NASA Technical Reports Server (NTRS)

Romani, Roger W.; Rajagopal, Mohan; Rogers, Forrest J.; Iglesias, Carlos A.

1995-01-01

Recent ROSAT and EUVE detections of spin-powered neutron stars suggest that many emit 'thermal' radiation, peaking in the EUV/soft X-ray band. These data constrain the neutron stars' thermal history, but interpretation requires comparison with model atmosphere computations, since emergent spectra depend strongly on the surface composition and magnetic field. As recent opacity computations show substantial change to absorption cross sections at neutron star photospheric conditions, we report here on new model atmosphere computations employing such data. The results are compared with magnetic atmosphere models and applied to PSR J0437-4715, a low field neutron star.

Outer crust of nonaccreting cold neutron stars

NASA Astrophysics Data System (ADS)

Rüster, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Jürgen

2006-03-01

The properties of the outer crust of nonaccreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables, updating in particular the classic work of Baym, Pethick, and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 are used and a thorough comparison of many modern theoretical nuclear models, both relativistic and nonrelativistic, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared to check their differences concerning the neutron drip line, magic neutron numbers, the equation of state, and the sequence of neutron-rich nuclei up to the drip line in the outer crust of nonaccreting cold neutron stars.

Establishing binarity amongst Galactic RV Tauri stars with a disc⋆

NASA Astrophysics Data System (ADS)

Manick, Rajeev; Van Winckel, Hans; Kamath, Devika; Hillen, Michel; Escorza, Ana

2017-01-01

Context. Over the last few decades it has become more evident that binarity is a prevalent phenomenon amongst RV Tauri stars with a disc. This study is a contribution to comprehend the role of binarity upon late stages of stellar evolution. Aims: In this paper we determine the binary status of six Galactic RV Tauri stars, namely DY Ori, EP Lyr, HP Lyr, IRAS 17038-4815, IRAS 09144-4933, and TW Cam, which are surrounded by a dusty disc. The radial velocities are contaminated by high-amplitude pulsations. We disentangle the pulsations from the orbital signal in order to determine accurate orbital parameters. We also place them on the HR diagram, thereby establishing their evolutionary nature. Methods: We used high-resolution spectroscopic time series obtained from the HERMES and CORALIE spectrographs mounted on the Flemish Mercator and Swiss Leonhard Euler Telescopes, respectively. An updated ASAS/AAVSO photometric time series is analysed to complement the spectroscopic pulsation search and to clean the radial velocities from the pulsations. The pulsation-cleaned orbits are fitted with a Keplerian model to determine the spectroscopic orbital parameters. We also calibrated a PLC relationship using type II cepheids in the LMC and apply the relation to our Galactic sample to obtain accurate distances and hence luminosities. Results: All six of the Galactic RV Tauri stars included in this study are binaries with orbital periods ranging between 650 and 1700 days and with eccentricities between 0.2 and 0.6. The mass functions range between 0.08 to 0.55 M⊙ which points to an unevolved low-mass companion. In the photometric time series we detect a long-term variation on the timescale of the orbital period for IRAS 17038-4815, IRAS 09144-4933, and TW Cam. Our derived stellar luminosities indicate that all except DY Ori and EP Lyr are post-AGB stars. DY Ori and EP Lyr are likely examples of the recently discovered dusty post-RGB stars. Conclusions: The orbital parameters

Velocity-induced collapses of stable neutron stars

NASA Astrophysics Data System (ADS)

Novak, J.

2001-09-01

The collapse of spherical neutron stars is studied in General Relativity. The initial state is a stable neutron star to which an inward radial kinetic energy has been added through some velocity profile. For two different equations of state and two different shapes of velocity profiles, it is found that neutron stars can collapse to black holes for high enough inward velocities, provided that their masses are higher than some minimal value, depending on the equation of state. For a polytropic equation of state of the form p=Krho gamma, with gamma = 2 it is found to be 1.16 ( (K)/(0.1) right )0.5 Msun, whereas for a more realistic one (described in Pons et al. \\cite{PonREPL00}), it is 0.36 Msun . In some cases of collapse forming a black hole, part of the matter composing the initial neutron star can be ejected through a shock, leaving only a fraction of the initial mass to form a black hole. Therefore, black holes of very small masses can be formed and, in particular, the mass scaling relation, as a function of initial velocity, takes the form discovered by Choptuik (\\cite{Cho93}) for critical collapses.

Constraints on Bygone Nucleosynthesis of Accreting Neutron Stars

DOE PAGES

Meisel, Zach; Deibel, Alex

2017-03-06

Nuclear burning near the surface of an accreting neutron star produces ashes that, when compressed deeper by further accretion, alter the star’s thermal and compositional structure. Bygone nucleosynthesis can be constrained by the impact of compressed ashes on the thermal relaxation of quiescent neutron star transients. In particular, Urca cooling nuclei pairs in nuclear burning ashes that cool the neutron star crust via neutrino emission from e --capture/β --decay cycles and provide signatures of prior nuclear burning over the ~century timescales it takes to accrete to the e --capture depth of the strongest cooling pairs. By using crust cooling modelsmore » of the accreting neutron star transient MAXI J0556-332, we show that this source likely lacked Type I X-ray bursts and superbursts ≳120 years ago. Reduced nuclear physics uncertainties in rp-process reaction rates and e --capture weak transition strengths for low-lying transitions will improve nucleosynthesis constraints using this technique.« less

Unlocking_Secrets_of_Neutron_Stars_with_NICER

NASA Image and Video Library

2017-05-25

Though we know neutron stars are small and extremely dense, there are still many aspects of these remnants of explosive deaths of other stars that we have yet to understand. NICER, a facility to be mounted on the outside of the International Space Station, seeks to find the answers to some of the questions still being asked about neutron stars. By capturing the arrival time and energy of the x-ray photons produced by pulsars emitted by neutron stars, NICER seeks answer decades-old questions about extreme forms of matter and energy. Data from NICER will also be used in Sextant, an on-board demonstration of pulsar-based navigation. Learn more about: https://www.nasa.gov/mission_pages/station/research/experiments/1966.html and keep up with all the science being conducted aboard your orbiting laboratory by visiting: https://www.nasa.gov/iss-science/ISS Research Overview on nasa.gov http://www.twitter.com/ISS_Research on Twitter.

Testing the Formation Scenarios of Binary Neutron Star Systems with Measurements of the Neutron Star Moment of Inertia

NASA Astrophysics Data System (ADS)

Newton, William G.; Steiner, Andrew W.; Yagi, Kent

2018-03-01

Two low-mass (M < 1.4 M ⊙) neutron stars, J0737-3039B and the companion to J1756-2251, show strong evidence of being formed in an ultra-stripped supernova explosion (US-SN) with a ONeMg or Fe progenitor. Using systematically generated sets of equations of state we map out the relationship between the moment of inertia of J0737-3039A, a candidate for a moment of inertia measurement within a decade, and the binding energy of the two low-mass neutron stars. This relationship, similar to the I-Love-Q relations, is more robust than a previously explored correlation between the binding energy and the slope of the nuclear symmetry energy L. We find that, if either J0737-3039B or the J1756-2251 companion were formed in a US-SN, no more than 0.06 M ⊙ could have been lost from the progenitor core. Furthermore, a measurement of the moment of inertia of J0737-3039A to within 10% accuracy can discriminate between formation scenarios and, given current constraints on the predicted core mass loss, potentially rule them out. Advanced LIGO can potentially measure the neutron star tidal polarizability to equivalent accuracy which, using the I-Love-Q relations, would obtain similar constraints on the formation scenarios. Such information would help constrain important aspects of binary evolution used for population synthesis predictions of the rate of binary neutron star mergers and resulting electromagnetic and gravitational wave signals. Further progress needs to be made in modeling the core-collapse process that leads to low-mass neutron stars, particularly in making robust predictions for the mass loss from the progenitor core.

A Statistical Study on Neutron Star Masses

NASA Astrophysics Data System (ADS)

Cheng, Z.; Zhang, C. M.; Zhao, Y. H.; Wang, D. H.; Pan, Y. Y.; Lei, Y. J.

2013-11-01

We investigate the measurement of neutron star masses in different population of binaries. Based on the collection of the orbital parameters of 40 systems (46 sources), we apply the boot-strap method together with the Monte Carlo method to reconstruct the likelihood curves for each source separately. The cumulative analysis of the simulation result shows that the neutron star masses in X-ray systems and radio systems obey different distributions, and no evidence for the bimodal distribution could be found. Employing the Bayesian statistical techniques, we find that the most likely distributions for the high mass X-ray binaries (HMXBs), low mass X-ray binaries (LMXBs), double neutron star (DNS) systems, and neutron star-white dwarf (NS-WD) binary systems are (1.340±0.230) M_{⊙}, (1.505±0.125) M_{⊙}, (1.335±0.055) M_{⊙}, and (1.495±0.225) M_{⊙}, respectively. The statistical distribution has no significant deviation from the standard neutron star formation mechanism. It is noticed that the statistical results of the center masses of LMXBs and NS-WD systems are significantly higher than the other groups by about 0.16 M_{⊙}, which could be regarded as the evidence of accretion episodes. And if we regard the HMXBs and LMXBs as the progenitors of DNS and NS-WD systems, then we can draw the conclusion that the accretion effect must be very week during the evolution trajectory from HMXBs to DNS systems, and this could be the reason why the masses of DNS systems have such a narrow distribution.

ARE THE kHz QPO LAGS IN NEUTRON STAR 4U 1608–52 DUE TO REVERBERATION?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cackett, Edward M., E-mail: ecackett@wayne.edu

2016-08-01

X-ray reverberation lags have recently been discovered in both active galactic nuclei (AGNs) and black hole X-ray binaries. A recent study of the neutron star low-mass X-ray binary (LMXB) 4U 1608 52 has also shown significant lags, whose properties hint at a reverberation origin. Here, we adapt general relativistic ray tracing impulse response functions used to model X-ray reverberation in AGNs for neutron star LMXBs. Assuming that relativistic reflection forms the broad iron line and associated reflection continuum, we use reflection fits to the energy spectrum along with the impulse response functions to calculate the expected lags as a functionmore » of energy over the range of observed kHz quasi-periodic oscillation (QPO) frequencies in 4U 1608 52. We find that the lag energy spectrum is expected to increase with increasing energy above 8 keV, while the observed lags in 4U 1608 52 show the opposite behavior. This demonstrates that the lags in the lower kHz QPO of 4U 1608 52 are not solely due to reverberation. We do note, however, that the models appear to be more consistent with the much flatter lag energy spectrum observed in the upper kHz QPO of several neutron star LMXBs, suggesting that lower and upper kHz QPOs may have different origins.« less

Dissertation Award in Nuclear Physics Recipient: Astromaterials in Neutron Stars

NASA Astrophysics Data System (ADS)

Caplan, Matthew E.

2017-09-01

Stars freeze. As they age and cool white dwarfs and neutron stars crystallize, with remarkable materials forming in their interiors. These `astromaterials' have structures similar to terrestrial crystalline solids and liquid crystals, though they are over a trillion times denser. Notably, because their material properties affect the observable properties of the star, astromaterials must be understood to interpret observations of neutron stars. Thus, astromaterial science can be thought of as an interdisciplinary field, using techniques from material science to study nuclear physics systems with astrophysical relevance. In this talk, I will discuss recent results from simulations of astromaterials and how we use these results to interpret observations of neutron stars in X-ray binaries. In addition, I will discuss how nuclear pasta, in neutron stars, forms structures remarkably similar to biophysical membranes seen in living organisms.

Constraining the mass and radius of neutron stars in globular clusters

NASA Astrophysics Data System (ADS)

Steiner, A. W.; Heinke, C. O.; Bogdanov, S.; Li, C. K.; Ho, W. C. G.; Bahramian, A.; Han, S.

2018-05-01

We analyse observations of eight quiescent low-mass X-ray binaries in globular clusters and combine them to determine the neutron star mass-radius curve and the equation of state of dense matter. We determine the effect that several uncertainties may have on our results, including uncertainties in the distance, the atmosphere composition, the neutron star maximum mass, the neutron star mass distribution, the possible presence of a hotspot on the neutron star surface, and the prior choice for the equation of state of dense matter. The distance uncertainty is implemented in a new Gaussian blurring method that can be directly applied to the probability distribution over mass and radius. We find that the radius of a 1.4 solar mass neutron star is most likely from 10 to 14 km and that tighter constraints are only possible with stronger assumptions about the nature of the neutron stars, the systematics of the observations, or the nature of dense matter. Strong phase transitions in the equation of state are preferred, and in this case, the radius is likely smaller than 12 km. However, radii larger than 12 km are preferred if the neutron stars have uneven temperature distributions.

Nearby stars of the Galactic disk and halo. III.

NASA Astrophysics Data System (ADS)

Fuhrmann, K.

2004-01-01

High-resolution spectroscopic observations of about 150 nearby stars or star systems are presented and discussed. The study of these and another 100 objects of the previous papers of this series implies that the Galaxy became reality 13 or 14 Gyr ago with the implementation of a massive, rotationally-supported population of thick-disk stars. The very high star formation rate in that phase gave rise to a rapid metal enrichment and an expulsion of gas in supernovae-driven Galactic winds, but was followed by a star formation gap for no less than three billion years at the Sun's galactocentric distance. In a second phase, then, the thin disk - our ``familiar Milky Way'' - came on stage. Nowadays it traces the bright side of the Galaxy, but it is also embedded in a huge coffin of dead thick-disk stars that account for a large amount of baryonic dark matter. As opposed to this, cold-dark-matter-dominated cosmologies that suggest a more gradual hierarchical buildup through mergers of minor structures, though popular, are a poor description for the Milky Way Galaxy - and by inference many other spirals as well - if, as the sample implies, the fossil records of its long-lived stars do not stick to this paradigm. Apart from this general picture that emerges with reference to the entire sample stars, a good deal of the present work is however also concerned with detailed discussions of many individual objects. Among the most interesting we mention the blue straggler or merger candidates HD 165401 and HD 137763/HD 137778, the likely accretion of a giant planet or brown dwarf on 59 Vir in its recent history, and HD 63433 that proves to be a young solar analog at \\tau˜200 Myr. Likewise, the secondary to HR 4867, formerly suspected non-single from the Hipparcos astrometry, is directly detectable in the high-resolution spectroscopic tracings, whereas the visual binary \\chi Cet is instead at least triple, and presumably even quadruple. With respect to the nearby young stars a

Probing the Galactic Potential with Next-generation Observations of Disk Stars

NASA Astrophysics Data System (ADS)

Sumi, T.; Johnston, K. V.; Tremaine, S.; Spergel, D. N.; Majewski, S. R.

2009-07-01

Our current knowledge of the rotation curve of the Milky Way is remarkably poor compared to other galaxies, limited by the combined effects of extinction and the lack of large samples of stars with good distance estimates and proper motions. Near-future surveys promise a dramatic improvement in the number and precision of astrometric, photometric, and spectroscopic measurements of stars in the Milky Way's disk. We examine the impact of such surveys on our understanding of the Galaxy by "observing" particle realizations of nonaxisymmetric disk distributions orbiting in an axisymmetric halo with appropriate errors and then attempting to recover the underlying potential using a Markov Chain Monte Carlo approach. We demonstrate that the azimuthally averaged gravitational force field in the Galactic plane—and hence, to a lesser extent, the Galactic mass distribution—can be tightly constrained over a large range of radii using a variety of types of surveys so long as the error distribution of the measurements of the parallax, proper motion, and radial velocity are well understood and the disk is surveyed globally. One advantage of our method is that the target stars can be selected nonrandomly in real or apparent-magnitude space to ensure just such a global sample without biasing the results. Assuming that we can always measure the line-of-sight velocity of a star with at least 1 km s-1 precision, we demonstrate that the force field can be determined to better than ~1% for Galactocentric radii in the range R = 4-20 kpc using either: (1) small samples (a few hundred stars) with very accurate trigonometric parallaxes and good proper-motion measurements (uncertainties δ p,tri lsim 10 μas and δμ lsim 100 μas yr-1 respectively); (2) modest samples (~1000 stars) with good indirect parallax estimates (e.g., uncertainty in photometric parallax δ p,phot~ 10%-20%) and good proper-motion measurements (δμ ~ 100 μas yr-1) or (3) large samples (~104 stars) with good

Gravitational waves from neutron star excitations in a binary inspiral

NASA Astrophysics Data System (ADS)

Parisi, Alessandro; Sturani, Riccardo

2018-02-01

In the context of a binary inspiral of mixed neutron star-black hole systems, we investigate the excitation of the neutron star oscillation modes by the orbital motion. We study generic eccentric orbits and show that tidal interaction can excite the f -mode oscillations of the star by computing the amount of energy and angular momentum deposited into the star by the orbital motion tidal forces via closed form analytic expressions. We study the f -mode oscillations of cold neutron stars using recent microscopic nuclear equations of state, and we compute their imprint into the emitted gravitational waves.

Neutron star dynamos and the origins of pulsar magnetism

NASA Technical Reports Server (NTRS)

Thompson, Christopher; Duncan, Robert C.

1993-01-01

Neutron star convection is a transient phenomenon and has an extremely high magnetic Reynolds number. In this sense, a neutron star dynamo is the quintessential fast dynamo. The convective motions are only mildly turbulent on scales larger than the approximately 100 cm neutrino mean free path, but the turbulence is well developed on smaller scales. Several fundamental issues in the theory of fast dynamos are raised in the study of a neutron star dynamo, in particular the possibility of dynamo action in mirror-symmetric turbulence. It is argued that in any high magnetic Reynolds number dynamo, most of the magnetic energy becomes concentrated in thin flux ropes when the field pressure exceeds the turbulent pressure at the smallest scale of turbulence. In addition, the possibilities for dynamo action during the various (pre-collapse) stages of convective motion that occur in the evolution of a massive star are examined, and the properties of white dwarf and neutron star progenitors are contrasted.

Outer crust of nonaccreting cold neutron stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruester, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Juergen

The properties of the outer crust of nonaccreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables, updating in particular the classic work of Baym, Pethick, and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 are used and a thorough comparison of many modern theoretical nuclear models, both relativistic and nonrelativistic, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared to check their differences concerning the neutron drip line, magic neutron numbers, the equationmore » of state, and the sequence of neutron-rich nuclei up to the drip line in the outer crust of nonaccreting cold neutron stars.« less

The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars

NASA Astrophysics Data System (ADS)

Dauphas, Nicolas

2005-06-01

Some heavy elements (with atomic number A > 69) are produced by the `rapid' (r)-process of nucleosynthesis, where lighter elements are bombarded with a massive flux of neutrons. Although this is characteristic of supernovae and neutron star mergers, uncertainties in where the r-process occurs persist because stellar models are too crude to allow precise quantification of this phenomenon. As a result, there are many uncertainties and assumptions in the models used to calculate the production ratios of actinides (like uranium-238 and thorium-232). Current estimates of the U/Th production ratio range from ~0.4 to 0.7. Here I show that the U/Th abundance ratio in meteorites can be used, in conjunction with observations of low-metallicity stars in the halo of the Milky Way, to determine the U/Th production ratio very precisely . This value can be used in future studies to constrain the possible nuclear mass formulae used in r-process calculations, to help determine the source of Galactic cosmic rays, and to date circumstellar grains. I also estimate the age of the Milky Way ( in a way that is independent of the uncertainties associated with fluctuations in the microwave background or models of stellar evolution.

Applicaton of the Calculating Formula for Mean Neutron Exposure on Barium stars

NASA Astrophysics Data System (ADS)

Zhang, F. H.; Zhang, L.; Cui, W. Y.; Zhang, B.

2017-11-01

Latest studies have shown that, in the s-process nucleosynthesis model for the low-mass asymptotic giant branch (AGB) star with (13C) pocket radiative burning during the interpulse period, the distribution of neutron exposures in the nucleosynthesis region can be regarded as an exponential function, and the relation between the mean neutron exposure (τ0) and the model parameters is (τ0} = - Δ τ/ln [q/(1 - r + q)]), in which (Δ τ) is the exposure value of each neutron irradiation, (r) is the overlap factor, and (q) is the mass ratio of the (13C) shell to the He intershell. In this paper the formula is applied to 26 samples of barium stars to test its reliability, and furthermore the neutron exposure nature in the AGB companion stars of 26 barium stars are analyzed. The results show that, the formula is reliable; in the AGB companion stars of 26 barium stars, at least 8 stars definitely have and 12 stars are highly likely to have exponential distribution of neutron exposures, while 4 stars tend to experience single neutron exposure; most of the AGB companion stars may have experienced fewer times of neutron irradiations before the element abundance distribution of the s-process comes to asymptotic condition.

Probing axions with neutron star inspirals and other stellar processes

NASA Astrophysics Data System (ADS)

Hook, Anson; Huang, Junwu

2018-06-01

In certain models of a QCD axion, finite density corrections to the axion potential can result in the axion being sourced by large dense objects. There are a variety of ways to test this phenomenon, but perhaps the most surprising effect is that the axion can mediate forces between neutron stars that can be as strong as gravity. These forces can be attractive or repulsive and their presence can be detected by Advanced LIGO observations of neutron star inspirals. By a numerical coincidence, axion forces between neutron stars with gravitational strength naturally have an associated length scale of tens of kilometers or longer, similar to that of a neutron star. Future observations of neutron star mergers in Advanced LIGO can probe many orders of magnitude of axion parameter space. Because the axion is only sourced by large dense objects, the axion force evades fifth force constraints. We also outline several other ways to probe this phenomenon using electromagnetic signals associated with compact objects.

Searching for X-ray Pulsations from Neutron Stars Using NICER

NASA Astrophysics Data System (ADS)

Ray, Paul S.; Arzoumanian, Zaven; Bogdanov, Slavko; Bult, Peter; Chakrabarty, Deepto; Guillot, Sebastien; Kust Harding, Alice; Ho, Wynn C. G.; Lamb, Frederick K.; Mahmoodifar, Simin; Miller, M. Coleman; Strohmayer, Tod E.; Wilson-Hodge, Colleen A.; Wolff, Michael Thomas

2017-08-01

The Neutron Star Interior Composition Explorer (NICER) presents an exciting new capability for discovering new modulation properties of X-ray emitting neutron stars, including large area, low background, extremely precise absolute time stamps, superb low-energy response and flexible scheduling. The Pulsation Searches and Multiwavelength Coordination working group has designed a 2.5 Ms observing program to search for pulsations and characterize the modulation properties of about 30 known or suspected neutron star sources across a number of source categories. A key early goal will be to search for pulsations from millisecond pulsars that might exhibit thermal pulsations from the surface suitable for pulse profile modeling to constrain the neutron star equation of state. In addition, we will search for pulsations from transitional millisecond pulsars, isolated neutron stars, LMXBs, accretion-powered millisecond pulsars, central compact objects and other sources. We will present our science plan and initial results from the first months of the NICER mission.

Searching for X-ray Pulsations from Neutron Stars Using NICER

NASA Astrophysics Data System (ADS)

Ray, Paul S.; Arzoumanian, Zaven; Gendreau, Keith C.; Bogdanov, Slavko; Bult, Peter; Chakrabarty, Deepto; Chakrabarty, Deepto; Guillot, Sebastien; Harding, Alice; Ho, Wynn C. G.; Lamb, Frederick; Mahmoodifar, Simin; Miller, Cole; Strohmayer, Tod; Wilson-Hodge, Colleen; Wolff, Michael T.; NICER Science Team Working Group on Pulsation Searches and Multiwavelength Coordination

2018-01-01

The Neutron Star Interior Composition Explorer (NICER) presents an exciting new capability for discovering new modulation properties of X-ray emitting neutron stars, including large area, low background, extremely precise absolute time stamps, superb low-energy response and flexible scheduling. The Pulsation Searches and Multiwavelength Coordination working group has designed a 2.5 Ms observing program to search for pulsations and characterize the modulation properties of about 30 known or suspected neutron star sources across a number of source categories. A key early goal will be to search for pulsations from millisecond pulsars that might exhibit thermal pulsations from the surface suitable for pulse profile modeling to constrain the neutron star equation of state. In addition, we will search for pulsations from transitional millisecond pulsars, isolated neutron stars, LMXBs, accretion-powered millisecond pulsars, central compact objects and other sources. We present our science plan and initial results from the first months of the NICER mission.

Mass ejection by strange star mergers and observational implications.

PubMed

Bauswein, A; Janka, H-T; Oechslin, R; Pagliara, G; Sagert, I; Schaffner-Bielich, J; Hohle, M M; Neuhäuser, R

2009-07-03

We determine the Galactic production rate of strangelets as a canonical input to calculations of the measurable cosmic ray flux of strangelets by performing simulations of strange star mergers and combining the results with recent estimates of stellar binary populations. We find that the flux depends sensitively on the bag constant of the MIT bag model of QCD and disappears for high values of the bag constant and thus more compact strange stars. In the latter case, strange stars could coexist with ordinary neutron stars as they are not converted by the capture of cosmic ray strangelets. An unambiguous detection of an ordinary neutron star would then not rule out the strange matter hypothesis.

Triaxial instabilities in rapidly rotating neutron stars

NASA Astrophysics Data System (ADS)

Basak, Arkadip

2018-06-01

Viscosity driven bar mode secular instabilities of rapidly rotating neutron stars are studied using LORENE/Nrotstar code. These instabilities set a more rigorous limit to the rotation frequency of a neutron star than the Kepler frequency/mass-shedding limit. The procedure employed in the code comprises of perturbing an axisymmetric and stationary configuration of a neutron star and studying its evolution by constructing a series of triaxial quasi-equilibrium configurations. Symmetry breaking point was found out for Polytropic as well as 10 realistic equations of states (EOS) from the CompOSE data base. The concept of piecewise polytropic EOSs has been used to comprehend the rotational instability of Realistic EOSs and validated with 19 different Realistic EOSs from CompOSE. The possibility of detecting quasi-periodic gravitational waves from viscosity driven instability with ground-based LIGO/VIRGO interferometers is also discussed very briefly.

Stability analysis of magnetized neutron stars - a semi-analytic approach

NASA Astrophysics Data System (ADS)

Herbrik, Marlene; Kokkotas, Kostas D.

2017-04-01

We implement a semi-analytic approach for stability analysis, addressing the ongoing uncertainty about stability and structure of neutron star magnetic fields. Applying the energy variational principle, a model system is displaced from its equilibrium state. The related energy density variation is set up analytically, whereas its volume integration is carried out numerically. This facilitates the consideration of more realistic neutron star characteristics within the model compared to analytical treatments. At the same time, our method retains the possibility to yield general information about neutron star magnetic field and composition structures that are likely to be stable. In contrast to numerical studies, classes of parametrized systems can be studied at once, finally constraining realistic configurations for interior neutron star magnetic fields. We apply the stability analysis scheme on polytropic and non-barotropic neutron stars with toroidal, poloidal and mixed fields testing their stability in a Newtonian framework. Furthermore, we provide the analytical scheme for dropping the Cowling approximation in an axisymmetric system and investigate its impact. Our results confirm the instability of simple magnetized neutron star models as well as a stabilization tendency in the case of mixed fields and stratification. These findings agree with analytical studies whose spectrum of model systems we extend by lifting former simplifications.

Globular Cluster Contributions to the Galactic Halo

NASA Astrophysics Data System (ADS)

Martell, Sarah; Grebel, Eva; Lai, David

2010-08-01

The goal of this project is to confirm chemically that globular clusters are the source of as much as half the population of the Galactic halo. Using moderate-resolution spectroscopy from the SEGUE survey, we have identified a previously unknown population of halo field giants with distinctly strong CN features. CN variations are typically only observed in globular clusters, so these stars are interpreted as immigrants to the halo that originally formed in globular clusters. In one night of Keck/HIRES time, we will obtain high-quality, high- resolution spectra for five such stars, and determine abundances of O, Na, Mg, Al, alpha, iron-peak and neutron-capture elements. With this information we can state clearly whether these unusual CN-strong halo stars carry the full abundance pattern seen in CN-strong globular cluster stars, with depleted C, O, and Mg and enhanced N, Na, and Al. This type of coarse ``chemical tagging'' will allow a clearer division of the Galactic halo into contributions from globular clusters and from dwarf galaxies, and will place constraints on theoretical models of globular cluster formation and evolution.

Magnetic fields in Neutron Stars

NASA Astrophysics Data System (ADS)

Viganò, D.; Pons, J. A.; Miralles, J. A.; Rea, N.

2015-05-01

Isolated neutron stars show a diversity in timing and spectral properties, which has historically led to a classification in different sub-classes. The magnetic field plays a key role in many aspects of the neutron star phenomenology: it regulates the braking torque responsible for their timing properties and, for magnetars, it provides the energy budget for the outburst activity and high quiescent luminosities (usually well above the rotational energy budget). We aim at unifying this observational variety by linking the results of the state-of-the-art 2D magneto-thermal simulations with observational data. The comparison between theory and observations allows to place two strong constraints on the physical properties of the inner crust. First, strong electrical currents must circulate in the crust, rather than in the star core. Second, the innermost part of the crust must be highly resistive, which is in principle in agreement with the presence of a novel phase of matter so-called nuclear pasta phase.

Gamma-ray bursts generated from phase transition of neutron stars to quark stars

NASA Astrophysics Data System (ADS)

Shu, Xiao-Yu; Huang, Yong-Feng; Zong, Hong-Shi

2017-02-01

The evolution of compact stars is believed to be able to produce various violent phenomena in our universe. In this paper, we discuss the possibility that gamma-ray bursts (GRBs) might result from the phase transition of a neutron star to a quark star and calculate the energy released from the conversion. In our study, we utilize the relativistic mean field (RMF) theory to describe the hadronic phase of neutron stars, while an improved quasi-particle model is adopted to describe the quark phase of quark stars. With quark matter equation-of-state (EOS) more reliable than models used before, it is found that the energy released is of the order of 1052 erg, which confirms the validity of the phase transition model.

Ancient Black Hole Speeds Through Sun's Galactic Neighborhood, Devouring Companion Star

NASA Astrophysics Data System (ADS)

2001-09-01

Astronomers using the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope have found an ancient black hole speeding through the Sun's Galactic neighborhood, devouring a small companion star as the pair travels in an eccentric orbit looping to the outer reaches of our Milky Way Galaxy. The scientists believe the black hole is the remnant of a massive star that lived out its brief life billions of years ago and later was gravitationally kicked from its home star cluster to wander the Galaxy with its companion. "This discovery is the first step toward filling in a missing chapter in the history of our Galaxy," said Felix Mirabel, an astrophysicist at the Institute for Astronomy and Space Physics of Argentina and French Atomic Energy Commission. "We believe that hundreds of thousands of very massive stars formed early in the history of our Galaxy, but this is the first black hole remnant of one of those huge primeval stars that we've found." "This also is the first time that a black hole's motion through space has been measured," Mirabel added. A black hole is a dense concentration of mass with a gravitational pull so strong that not even light can escape it. The research is reported in the Sept. 13 issue of the scientific journal Nature. XTE J1118+480 The object is called XTE J1118+480 and was discovered by the Rossi X-Ray satellite on March 29, 2000. Later observations with optical and radio telescopes showed that it is about 6,000 light-years from Earth and that it is a "microquasar" in which material sucked by the black hole from its companion star forms a hot, spinning disk that spits out "jets" of subatomic particles that emit radio waves. Most of the stars in our Milky Way Galaxy are within a thin disk, called the plane of the Galaxy. However, there also are globular clusters, each containing hundreds of thousands of the oldest stars in the Galaxy which orbit the Galaxy's center in paths that take them far from the Galaxy's plane. XTE J

Hadron-quark crossover and hot neutron stars at birth

NASA Astrophysics Data System (ADS)

Masuda, Kota; Hatsuda, Tetsuo; Takatsuka, Tatsuyuki

2016-02-01

We construct a new isentropic equation of state (EOS) at finite temperature, "CRover," on the basis of the hadron-quark crossover at high density. By using the new EOS, we study the structure of hot neutron stars at birth with typical lepton fraction (Y_l=0.3-0.4) and typical entropy per baryon (hat {S}=1{-}2). Due to the gradual appearance of quark degrees of freedom at high density, the temperature T and the baryon density ρ at the center of hot neutron stars with hadron-quark crossover are found to be smaller than those without the crossover by a factor of two or more. Typical energy release due to the contraction of a hot neutron star to a cold neutron star with mass M=1.4 M_{⊙} is shown to be about 0.04 M_{⊙}, with a spin-up rate of about 14%.

An ultraluminous X-ray source powered by an accreting neutron star.

PubMed

Bachetti, M; Harrison, F A; Walton, D J; Grefenstette, B W; Chakrabarty, D; Fürst, F; Barret, D; Beloborodov, A; Boggs, S E; Christensen, F E; Craig, W W; Fabian, A C; Hailey, C J; Hornschemeier, A; Kaspi, V; Kulkarni, S R; Maccarone, T; Miller, J M; Rana, V; Stern, D; Tendulkar, S P; Tomsick, J; Webb, N A; Zhang, W W

2014-10-09

The majority of ultraluminous X-ray sources are point sources that are spatially offset from the nuclei of nearby galaxies and whose X-ray luminosities exceed the theoretical maximum for spherical infall (the Eddington limit) onto stellar-mass black holes. Their X-ray luminosities in the 0.5-10 kiloelectronvolt energy band range from 10(39) to 10(41) ergs per second. Because higher masses imply less extreme ratios of the luminosity to the isotropic Eddington limit, theoretical models have focused on black hole rather than neutron star systems. The most challenging sources to explain are those at the luminous end of the range (more than 10(40) ergs per second), which require black hole masses of 50-100 times the solar value or significant departures from the standard thin disk accretion that powers bright Galactic X-ray binaries, or both. Here we report broadband X-ray observations of the nuclear region of the galaxy M82 that reveal pulsations with an average period of 1.37 seconds and a 2.5-day sinusoidal modulation. The pulsations result from the rotation of a magnetized neutron star, and the modulation arises from its binary orbit. The pulsed flux alone corresponds to an X-ray luminosity in the 3-30 kiloelectronvolt range of 4.9 × 10(39) ergs per second. The pulsating source is spatially coincident with a variable source that can reach an X-ray luminosity in the 0.3-10 kiloelectronvolt range of 1.8 × 10(40) ergs per second. This association implies a luminosity of about 100 times the Eddington limit for a 1.4-solar-mass object, or more than ten times brighter than any known accreting pulsar. This implies that neutron stars may not be rare in the ultraluminous X-ray population, and it challenges physical models for the accretion of matter onto magnetized compact objects.

Gamma-ray lines from neutron stars as probes of fundamental physics

NASA Technical Reports Server (NTRS)

Brecher, K.

1978-01-01

The detection of gamma-ray lines produced at the surface of neutron stars will serve to test both the strong and gravitational interactions under conditions unavailable in terrestrial laboratories. Observation of a single redshifted gamma-ray line, combined with an estimate of the mass of the star will serve as a strong constraint on allowable equations of state of matter at supernuclear densities. Detection of two redshifted lines arising from different physical processes at the neutron star surface can provide a test of the strong principle of equivalence. Expected fluxes of nuclear gamma-ray lines from accreting neutron stars were calculated, including threshold, radiative transfer and redshift effects. The most promising probes of neutron star structure are the deuterium formation line and the positron annihilation line. Detection of sharp redshifted gamma-ray lines from X-ray sources such as Cyg X-1 would argue strongly in favor of a neutron star rather than black hole identification for the object.

Star Formation Driven Galactic Winds at z~1.4

NASA Astrophysics Data System (ADS)

Weiner, Benjamin J.

2009-12-01

Galactic winds are a prime suspect for driving metals out of galaxies, creating the mass-metallicity relation, probably enriching the IGM, and explaining the low baryon fraction in galaxies. They may also be related to the quenching of star formation in red galaxies. However, it is unclear how efficiently winds couple to the ISM, and which types and masses of galaxies drove winds in the past. Spectroscopy of blueshifted Mg II absorption in galaxies at z~1.4 in the DEEP2 survey shows that winds are ubiquitous at that redshift (where the SFR in the bulk of galaxies is higher than today), and that they are driven by star formation. Many of these galaxies will become spirals rather than ellipticals, showing that SF-driven winds are part of the past history of many galaxies, but that such winds do not directly lead to quenching or deterrence of subsequent star formation.

White Dwarfs, Neutron Stars and Black Holes

ERIC Educational Resources Information Center

Szekeres, P.

1977-01-01

The three possible fates of burned-out stars: white dwarfs, neutron stars and black holes, are described in elementary terms. Characteristics of these celestial bodies, as provided by Einstein's work, are described. (CP)

Physics in strong magnetic fields near neutron stars

NASA Technical Reports Server (NTRS)

Harding, Alice K.

1991-01-01

Electromagnetic phenomena occurring in the strong magnetic fields of neutron stars are currently of great interest in high-energy astrophysics. Observations of rotation rate changes and cyclotron lines in pulsars and gamma-ray bursts indicate that surface magnetic fields of neutron stars often exceed a trillion gauss. In fields this strong, where electrons behave much as if they were in bound atomic states, familiar processes undergo profound changes, and exotic processes become important. Strong magnetic fields affect the physics in several fundamental ways: energies perpendicular to the field are quantized, transverse momentum is not conserved, and electron-positron spin is important. Neutron stars therefore provide a unique laboratory for the study of physics in extremely high fields that cannot be generated on earth.

Accreting Millisecond Pulsars: Neutron Star Masses and Radii

NASA Technical Reports Server (NTRS)

Strohmayer, Tod

2004-01-01

High amplitude X-ray brightness oscillations during thermonuclear X-ray bursts were discovered with the Rossi X-ray Timing Explorer (RXTE) in early 1996. Spectral and timing evidence strongly supports the conclusion that these oscillations are caused by rotational modulation of the burst emission and that they reveal the spin frequency of neutron stars in low mass X-ray binaries. The recent discovery of X-ray burst oscillations from two accreting millisecond pulsars has confirmed this basic picture and provided a new route to measuring neutron star properties and constraining the dense matter equation of state. I will briefly summarize the current observational understanding of accreting millisecond pulsars, and describe recent attempts to determine the mass and radius of the neutron star in XTE J1814-338.

PALFA Discovers Neutron Stars on a Collision Course

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-03-01

Got any plans in 46 million years? If not, you should keep an eye out for PSR J1946+2052 around that time this upcoming merger of two neutron stars promises to be an exciting show!Survey SuccessAverage profile for PSR J1946+2052 at 1.43 GHz from a 2 hr observation from the Arecibo Observatory. [Stovall et al. 2018]It seems like we just wrote about the dearth of known double-neutron-star systems, and about how new surveys are doing their best to find more of these compact binaries. Observing these systems improves our knowledge of how pairs of evolved stars behave before they eventually spiral in, merge, and emit gravitational waves that detectors like the Laser Interferometer Gravitational-wave Observatory might observe.Todays study, led by Kevin Stovall (National Radio Astronomy Observatory), goes to show that these surveys are doing a great job so far! Yet another double-neutron-star binary, PSR J1946+2052, has now been discovered as part of the Arecibo L-Band Feed Array pulsar (PALFA) survey. This one is especially unique due to the incredible speed with which these neutron stars orbit each other and their correspondingly (relatively!) short timescale for merger.An Extreme ExampleThe PALFA survey, conducted with the enormous 305-meter radio dish at Arecibo, has thus far resulted in the discovery of 180 pulsars including two double-neutron-star systems. The most recent discovery by Stovall and collaborators brings that number up to three, for a grand total of 16 binary-neutron-star systems (confirmed and unconfirmed) known to date.The 305-m Arecibo Radio Telescope, built into the landscape at Arecibo, Puerto Rico. [NOAO/AURA/NSF/H. Schweiker/WIYN]The newest binary in this collection, PSR J1946+2052, exhibits a pulsar with a 17-millisecond spin period thatwhips around its compact companion at a terrifying rate: the binary period is just 1.88 hours. Follow-up observations with the Jansky Very Large Array and other telescopes allowed the team to identify the binarys

On obtaining neutron-star mass and radius constraints from quiescent low-mass X-ray binaries in the Galactic plane

NASA Astrophysics Data System (ADS)

Marino, Alessio; Degenaar, N.; Di Salvo, T.; Wijnands, R.; Burderi, L.; Iaria, R.

2018-06-01

X-ray spectral analysis of quiescent low-mass X-ray binaries (LMXBs) has been one of the most common tools to measure the radius of neutron stars (NSs) for over a decade. So far, this method has been mainly applied to NSs in globular clusters, primarily because of their well-constrained distances. Here, we study Chandra data of seven transient LMXBs in the Galactic plane in quiescence to investigate the potential of constraining the radius (and mass) of the NSs inhabiting these systems. We find that only two of these objects had X-ray spectra of sufficient quality to obtain reasonable constraints on the radius, with the most stringent being an upper limit of R ≲14.5 km for EXO 0748-676 (for assumed ranges for mass and distance). Using these seven sources, we also investigate systematic biases on the mass/radius determination; for Aql X-1 we find that omitting a power-law spectral component when it does not seem to be required by the data, results in peculiar trends in the obtained radius with changing mass and distance. For EXO 0748-676 we find that a slight variation in the lower limit of the energy range chosen for the fit leads to systematically different masses and radii. Finally, we simulated Athena spectra and found that some of the biases can be lifted when higher quality spectra are available and that, in general, the search for constraints on the equation of state of ultra-dense matter via NS radius and mass measurements may receive a considerable boost in the future.

The Galactic Center S-stars and the Hypervelocity Stars in the Galactic Halo: Two Faces of the Tidal Breakup of Stellar Binaries by the Central Massive Black Hole?

NASA Astrophysics Data System (ADS)

Zhang, Fupeng; Lu, Youjun; Yu, Qingjuan

2013-05-01

In this paper, we investigate the link between the hypervelocity stars (HVSs) discovered in the Galactic halo and the Galactic center (GC) S-stars, under the hypothesis that they are both the products of the tidal breakup of the same population of stellar binaries by the central massive black hole (MBH). By adopting several hypothetical models for binaries to be injected into the vicinity of the MBH and doing numerical simulations, we realize the tidal breakup processes of the binaries and their follow-up dynamical evolution. We find that many statistical properties of the detected HVSs and GC S-stars could be reproduced under some binary injecting models, and their number ratio can be reproduced if the stellar initial mass function is top-heavy (e.g., with slope ~ - 1.6). The total number of the captured companions is ~50 that have masses in the range ~3-7 M ⊙ and semimajor axes <~ 4000 AU and survive to the present within their main-sequence lifetime. The innermost one is expected to have a semimajor axis ~300-1500 AU and a pericenter distance ~10-200 AU, with a significant probability of being closer to the MBH than S2. Future detection of such a close star would offer an important test to general relativity. The majority of the surviving ejected companions of the GC S-stars are expected to be located at Galactocentric distances <~ 20 kpc, and have heliocentric radial velocities ~ - 500-1500 km s-1 and proper motions up to ~5-20 mas yr-1. Future detection of these HVSs may provide evidence for the tidal breakup formation mechanism of the GC S-stars.

Constraints on the symmetry energy from neutron star observations

NASA Astrophysics Data System (ADS)

Newton, W. G.; Gearheart, M.; Wen, De-Hua; Li, Bao-An

2013-03-01

The modeling of many neutron star observables incorporates the microphysics of both the stellar crust and core, which is tied intimately to the properties of the nuclear matter equation of state (EoS). We explore the predictions of such models over the range of experimentally constrained nuclear matter parameters, focusing on the slope of the symmetry energy at nuclear saturation density L. We use a consistent model of the composition and EoS of neutron star crust and core matter to model the binding energy of pulsar B of the double pulsar system J0737-3039, the frequencies of torsional oscillations of the neutron star crust and the instability region for r-modes in the neutron star core damped by electron-electron viscosity at the crust-core interface. By confronting these models with observations, we illustrate the potential of astrophysical observables to offer constraints on poorly known nuclear matter parameters complementary to terrestrial experiments, and demonstrate that our models consistently predict L < 70 MeV.

NICER observations of highly magnetized neutron stars: Initial results

NASA Astrophysics Data System (ADS)

Enoto, Teruaki; Arzoumanian, Zaven; Gendreau, Keith C.; Nynka, Melania; Kaspi, Victoria; Harding, Alice; Guver, Tolga; Lewandowska, Natalia; Majid, Walid; Ho, Wynn C. G.; NICER Team

2018-01-01

The Neutron star Interior Composition Explorer (NICER) was launched on June 3, 2017, and attached to the International Space Station. The large effective area of NICER in soft X-rays makes it a powerful tool not only for its primary science objective (diagnostics of the nuclear equation state) but also for studying neutron stars of various classes. As one of the NICER science working groups, the Magnetars and Magnetospheres (M&M) team coordinates monitoring and target of opportunity (ToO) observations of magnetized neutron stars, including magnetars, high-B pulsars, X-ray dim isolated neutron stars, and young rotation-powered pulsars. The M&M working group has performed simultaneous X-ray and radio observations of the Crab and Vela pulsars, ToO observations of the active anomalous X-ray pulsar 4U 0142+61, and a monitoring campaign for the transient magnetar SGR 0501+4516. Here we summarize the current status and initial results of the M&M group.

Tidal breakup of quadruple stars in the Galactic Centre

NASA Astrophysics Data System (ADS)

Fragione, Giacomo

2018-06-01

The most likely origin of hypervelocity stars (HVSs) is the tidal disruption of a binary star by the supermassive black hole (MBH) in the Galactic Centre (GC). However, HE0437-5439, a 9 M_⊙ B-type main-sequence star moving with a heliocentric radial velocity of about 720 km s^{-1} at a distance of ˜ 60{ kpc}, and the recent discovered hypervelocity binary candidate (HVB), traveling at ˜ 570 km s^{-1}, challenge this standard scenario. Recently, Fragione & Gualandris (2018) have demonstrated that the tidal breakup of a triple star leads to an insufficient rate. Observations show that quadruple stars made up of two binaries orbiting their common center of mass (the so-called 2+2 quadruples) are ≈4% of the stars in the solar neighborhood. Although rarer than triples, 2+2 quadruple stars may have a role in ejecting HVBs as due to their larger energy reservoir. We present a numerical study of 2+2 quadruple disruptions by the MBH in the GC and find that the production of HVBs has a probability ≲ 2 - 4%, which translates into an ejection rate of ≲ 1{ Gyr}^{-1}, comparable to the triple disruption scenario. Given the low ejection rate, we suggest that alternative mechanisms are responsible for the origin of HVBs, as the ejection from the interaction of a young star cluster with the MBH in the GC and the origin in the Large Magellanic Cloud.

Role of strangeness to the neutron star mass and cooling

NASA Astrophysics Data System (ADS)

Lee, Chang-Hwan; Lim, Yeunhwan; Hyun, Chang Ho; Kwak, Kyujin

2018-01-01

Neutron star provides unique environments for the investigation of the physics of extreme dense matter beyond normal nuclear saturation density. In such high density environments, hadrons with strange quarks are expected to play very important role in stabilizing the system. Kaons and hyperons are the lowest mass states with strangeness among meson and bayron families, respectively. In this work, we investigate the role of kaons and hyperons to the neutron star mass, and discuss their role in the neutron star cooling.

Gamma-ray and X-ray emission from the Galactic centre: hints on the nuclear star cluster formation history

NASA Astrophysics Data System (ADS)

Arca-Sedda, Manuel; Kocsis, Bence; Brandt, Timothy D.

2018-06-01

The Milky Way centre exhibits an intense flux in the gamma and X-ray bands, whose origin is partly ascribed to the possible presence of a large population of millisecond pulsars (MSPs) and cataclysmic variables (CVs), respectively. However, the number of sources required to generate such an excess is much larger than what is expected from in situ star formation and evolution, opening a series of questions about the formation history of the Galactic nucleus. In this paper we make use of direct N-body simulations to investigate whether these sources could have been brought to the Galactic centre by a population of star clusters that underwent orbital decay and formed the Galactic nuclear star cluster (NSC). Our results suggest that the gamma ray emission is compatible with a population of MSPs that were mass segregated in their parent clusters, while the X-ray emission is consistent with a population of CVs born via dynamical interactions in dense star clusters. Combining observations with our modelling, we explore how the observed γ ray flux can be related to different NSC formation scenarios. Finally, we show that the high-energy emission coming from the galactic central regions can be used to detect black holes heavier than 105M⊙ in nearby dwarf galaxies.

A new survey of nebulae around Galactic Wolf-Rayet stars in the northern sky

NASA Technical Reports Server (NTRS)

Miller, Grant J.; Chu, You-Hua

1993-01-01

Interference filter CCD images have been obtained in H-alpha and forbidden O III 5007 A for 62 Wolf-Rayet (W-R) stars, representing a complete survey of nebulae around Galactic W-R stars in the northern sky. We find probable new ring nebulae around W-R stars number 113, 116 and 132, and possible new ring nebulae around W-R stars number 133 and 153. All survey images showing nebulosities around W-R stars are presented in this paper. New physical information is derived from the improved images of known ring nebulae. The absence of ring nebulae around most W-R stars is discussed.

A debris disk around an isolated young neutron star.

PubMed

Wang, Zhongxiang; Chakrabarty, Deepto; Kaplan, David L

2006-04-06

Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk. Such 'fallback' is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar. The disk does not power the pulsar's X-ray emission but is passively illuminated by these X-rays. The estimated mass of the disk is of the order of 10 Earth masses, and its lifetime (> or = 10(6) years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars.

White dwarf stars and the age of the Galactic disk

NASA Technical Reports Server (NTRS)

Wood, M. A.

1990-01-01

The history of the Galaxy is written in its oldest stars, the white dwarf (WD) stars. Significant limits can be placed on both the Galactic age and star formation history. A wide range of input WD model sequences is used to derive the current limits to the age estimates suggested by fitting to the observed falloff in the WD luminosity function. The results suggest that the star formation rate over the history of the Galaxy has been relatively constant, and that the disk age lies in the range 6-12 billion years, depending upon the assumed structure of WD stars, and in particular on the core composition and surface helium layer mass. Using plausible mixed C/O core input models, the estimates for the disk age range from 8-10.5 Gyr, i.e.,sustantially younger than most age estimates for the halo globular clusters. After speculating on the significance of the results, expected observational and theoretical refinements which will further enhance the reliability of the method are discussed.

Gas cloud G2 can illuminate the black hole population near the galactic center.

PubMed

Bartos, Imre; Haiman, Zoltán; Kocsis, Bence; Márka, Szabolcs

2013-05-31

Galactic nuclei are expected to be densely populated with stellar- and intermediate-mass black holes. Exploring this population will have important consequences for the observation prospects of gravitational waves as well as understanding galactic evolution. The gas cloud G2 currently approaching Sgr A* provides an unprecedented opportunity to probe the black hole and neutron star population of the Galactic nucleus. We examine the possibility of a G2-cloud-black-hole encounter and its detectability with current x-ray satellites, such as Chandra and NuSTAR. We find that multiple encounters are likely to occur close to the pericenter, which may be detectable upon favorable circumstances. This opportunity provides an additional important science case for leading x-ray observatories to closely follow G2 on its way to the nucleus.

Dynamics of supernova remnants in the Galactic centre.

NASA Astrophysics Data System (ADS)

Bortolas, E.; Mapelli, M.; Spera, M.

The Galactic centre (GC) is a unique place to study the extreme dynamical processes occurring near a super-massive black hole (SMBH). Here we simulate a large set of binaries orbiting the SMBH while the primary member undergoes a supernova (SN) explosion, in order to study the impact of SN kicks on the orbits of stars and dark remnants in the GC. We find that SN explosions are efficient in scattering neutron stars and other light stars on new (mostly eccentric) orbits, while black holes (BHs) tend to retain memory of the orbit of their progenitor star. SN kicks are thus unable to eject BHs from the GC: a cusp of dark remnants may be lurking in the central parsec of our Galaxy.

Star Formation and Gas Dynamics in Galactic Disks: Physical Processes and Numerical Models

NASA Astrophysics Data System (ADS)

Ostriker, Eve C.

2011-04-01

Star formation depends on the available gaseous ``fuel'' as well as galactic environment, with higher specific star formation rates where gas is predominantly molecular and where stellar (and dark matter) densities are higher. The partition of gas into different thermal components must itself depend on the star formation rate, since a steady state distribution requires a balance between heating (largely from stellar UV for the atomic component) and cooling. In this presentation, I discuss a simple thermal and dynamical equilibrium model for the star formation rate in disk galaxies, where the basic inputs are the total surface density of gas and the volume density of stars and dark matter, averaged over ~kpc scales. Galactic environment is important because the vertical gravity of the stars and dark matter compress gas toward the midplane, helping to establish the pressure, and hence the cooling rate. In equilibrium, the star formation rate must evolve until the gas heating rate is high enough to balance this cooling rate and maintain the pressure imposed by the local gravitational field. In addition to discussing the formulation of this equilibrium model, I review the current status of numerical simulations of multiphase disks, focusing on measurements of quantities that characterize the mean properties of the diffuse ISM. Based on simulations, turbulence levels in the diffuse ISM appear relatively insensitive to local disk conditions and energetic driving rates, consistent with observations. It remains to be determined, both from observations and simulations, how mass exchange processes control the ratio of cold-to-warm gas in the atomic ISM.

Neutron stars interiors: Theory and reality

NASA Astrophysics Data System (ADS)

Stone, J. R.

2016-03-01

There are many fascinating processes in the universe which we observe in more detail thanks to increasingly sophisticated technology. One of the most interesting phenomena is the life cycle of stars, their birth, evolution and death. If the stars are massive enough, they end their lives in a core-collapse supernova explosion, one of the most violent events in the universe. As a result, the densest objects in the universe, neutron stars and/or black holes, are created. The physical basis of these events should be understood in line with observation. Unfortunately, available data do not provide adequate constraints for many theoretical models of dense matter. One of the most open areas of research is the composition of matter in the cores of neutron stars. Unambiguous fingerprints for the appearance and evolution of particular components, such as strange baryons and mesons, with increasing density, have not been identified. In particular, the hadron-quark phase transition remains a subject of intensive research. In this contribution we briefly survey the most promising observational and theoretical directions leading to progress in understanding high density matter in neutron stars. A possible way forward in modeling high-density matter is outlined, exemplified by the quark-meson-coupling model (QMC). This model makes connection between hadronic structure and the underlying quark make-up. It offers a natural explanation for the saturation of nuclear force and treats high-density matter, containing the full baryon octet, in terms of four uniquely defined parameters adjusted to properties of symmetric nuclear matter at saturation.

Constraining neutron-star tidal Love numbers with gravitational-wave detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flanagan, Eanna E.; Hinderer, Tanja

Ground-based gravitational wave detectors may be able to constrain the nuclear equation of state using the early, low frequency portion of the signal of detected neutron star-neutron star inspirals. In this early adiabatic regime, the influence of a neutron star's internal structure on the phase of the waveform depends only on a single parameter {lambda} of the star related to its tidal Love number, namely, the ratio of the induced quadrupole moment to the perturbing tidal gravitational field. We analyze the information obtainable from gravitational wave frequencies smaller than a cutoff frequency of 400 Hz, where corrections to the internal-structuremore » signal are less than 10%. For an inspiral of two nonspinning 1.4M{sub {center_dot}} neutron stars at a distance of 50 Megaparsecs, LIGO II detectors will be able to constrain {lambda} to {lambda}{<=}2.0x10{sup 37} g cm{sup 2} s{sup 2} with 90% confidence. Fully relativistic stellar models show that the corresponding constraint on radius R for 1.4M{sub {center_dot}} neutron stars would be R{<=}13.6 km (15.3 km) for a n=0.5 (n=1.0) polytrope with equation of state p{proportional_to}{rho}{sup 1+1/n}.« less

The Neutron Star Interior Composition Explorer (NICER)

NASA Technical Reports Server (NTRS)

Wilson-Hodge, Colleen A.; Gendreau, K.; Arzoumanian, Z.

2014-01-01

The Neutron Star Interior Composition Explorer (NICER) is an approved NASA Explorer Mission of Opportunity dedicated to the study of the extraordinary gravitational, electromagnetic, and nuclear-physics environments embodied by neutron stars. Scheduled to be launched in 2016 as an International Space Station payload, NICER will explore the exotic states of matter, using rotation-resolved spectroscopy of the thermal and non-thermal emissions of neutron stars in the soft (0.2-12 keV) X-ray band. Grazing-incidence "concentrator" optics coupled with silicon drift detectors, actively pointed for a full hemisphere of sky coverage, will provide photon-counting spectroscopy and timing registered to GPS time and position, with high throughput and relatively low background. The NICER project plans to implement a Guest Observer Program, which includes competitively selected user targets after the first year of flight operations. I will describe NICER and discuss ideas for potential Be/X-ray binary science.

Coulomb crystals in neutron star crust

NASA Astrophysics Data System (ADS)

Baiko, D. A.

2014-03-01

It is well known that neutron star crust in a wide range of mass densities and temperatures is in a crystal state. At a given density, the crystal is made of fully ionized atomic nuclei of a single species immersed in a nearly incompressible (i.e., constant and uniform) charge compensating background of electrons. This model is known as the Coulomb crystal model. In this talk we analyze thermodynamic and elastic properties of the Coulomb crystals and discuss various deviations from the ideal model. In particular, we study the Coulomb crystal behavior in the presence of a strong magnetic field, consider the effect of the electron gas polarizability, outline the main properties of binary Coulomb crystals, and touch the subject of quasi-free neutrons permeating the Coulomb crystal of ions in deeper layers of neutron star crust.

Neutron Star Structure in the Presence of Conformally Coupled Scalar Fields

NASA Technical Reports Server (NTRS)

Sultana, Joseph; Bose, Benjamin; Kazanas, Demosthenes

2014-01-01

Neutron star models are studied in the context of scalar-tensor theories of gravity in the presence of a conformally coupled scalar field, using two different numerical equations of state (EoS) representing different degrees of stiffness. In both cases we obtain a complete solution by matching the interior numerical solution of the coupled Einstein-scalar field hydrostatic equations, with an exact metric on the surface of the star. These are then used to find the effect of the scalar field and its coupling to geometry, on the neutron star structure, particularly the maximum neutron star mass and radius. We show that in the presence of a conformally coupled scalar field, neutron stars are less dense and have smaller masses and radii than their counterparts in the minimally coupled case, and the effect increases with the magnitude of the scalar field at the center of the star.

X-ray Observations of Neutron Stars

NASA Astrophysics Data System (ADS)

Enoto, Teruaki

A large diversity of neutron stars has been discovered by recent multi-wavelength observations from the radio band to the X-ray and gamma-ray energy range. Among different manifestation of neutron stars, magnetars are strongly magnetised objects with the magnetic field strength of B = 1014-15 G. Some of magnetars exhibit transient behaviours, in which activated state the magnetars radiate sporadic short bursts and enhanced persistent X-ray emission for a couple of weeks or more. The Suzaku X-ray satellite has observed 15 magnetars among 23 known sources in 2006-2013, including persistently bright sources and transient objects. We showed that the broadband magnetar spectra, including both of surface emission below 10 keV and magnetospheric power-law radiation above 10 keV, follow spectral evolution as a function of the magnetic field, in terms of wide-band spectral hardness ratio and of power-law photon index. Magnetars are also compared with other rotation powered pulsars on the correlation between X-ray luminosity and the spin-down luminosity. I will address future missions related with investigation of the nature of neutron stars.

Electromagnetic Chirps from Neutron Star-Black Hole Mergers

NASA Technical Reports Server (NTRS)

Schnittman, Jeremy D.; Dal Canton, Tito; Camp, Jordan B.; Tsang, David; Kelly, Bernard J.

2018-01-01

We calculate the electromagnetic signal of a gamma-ray flare coming from the surface of a neutron star shortly before merger with a black hole companion. Using a new version of the Monte Carlo radiation transport code Pandurata that incorporates dynamic spacetimes, we integrate photon geodesics from the neutron star surface until they reach a distant observer or are captured by the black hole. The gamma-ray light curve is modulated by a number of relativistic effects, including Doppler beaming and gravitational lensing. Because the photons originate from the inspiraling neutron star, the light curve closely resembles the corresponding gravitational waveform: a chirp signal characterized by a steadily increasing frequency and amplitude. We propose to search for these electromagnetic chirps using matched filtering algorithms similar to those used in LIGO data analysis.

Determining the properties of accretion-gap neutron stars

NASA Technical Reports Server (NTRS)

Kluzniak, Wlodzimierz; Michelson, Peter; Wagoner, Robert V.

1990-01-01

If neutron stars have radii as small as has been argued by some, observations of accretion-powered X-rays could verify the existence of innermost stable circular orbits (predicted by general relativity) around weakly magnetized neutron stars. This may be done by detecting X-ray emission from clumps of matter before and after they cross the gap (where matter cannot be supported by rotation) between the inner accretion disk and the stellar surface. Assuming the validity of general relativity, it would then be possible to determine the masses of such neutron stars independently of any knowledge of binary orbital parameters. If an accurate mass determination were already available through any of the methods conventionally used, the new mass determination method proposed here could then be used to quantitatively test strong field effects of gravitational theory.

The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars.

PubMed

Dauphas, Nicolas

2005-06-30

Some heavy elements (with atomic number A > 69) are produced by the 'rapid' (r)-process of nucleosynthesis, where lighter elements are bombarded with a massive flux of neutrons. Although this is characteristic of supernovae and neutron star mergers, uncertainties in where the r-process occurs persist because stellar models are too crude to allow precise quantification of this phenomenon. As a result, there are many uncertainties and assumptions in the models used to calculate the production ratios of actinides (like uranium-238 and thorium-232). Current estimates of the U/Th production ratio range from approximately 0.4 to 0.7. Here I show that the U/Th abundance ratio in meteorites can be used, in conjunction with observations of low-metallicity stars in the halo of the Milky Way, to determine the U/Th production ratio very precisely (0.57(+0.037)(-0.031). This value can be used in future studies to constrain the possible nuclear mass formulae used in r-process calculations, to help determine the source of Galactic cosmic rays, and to date circumstellar grains. I also estimate the age of the Milky Way (14.5(+2.8)(-2.2)Gyr in a way that is independent of the uncertainties associated with fluctuations in the microwave background or models of stellar evolution.

Holographic Quark Matter and Neutron Stars.

PubMed

Hoyos, Carlos; Jokela, Niko; Rodríguez Fernández, David; Vuorinen, Aleksi

2016-07-15

We use a top-down holographic model for strongly interacting quark matter to study the properties of neutron stars. When the corresponding equation of state (EOS) is matched with state-of-the-art results for dense nuclear matter, we consistently observe a first-order phase transition at densities between 2 and 7 times the nuclear saturation density. Solving the Tolman-Oppenheimer-Volkov equations with the resulting hybrid EOSs, we find maximal stellar masses in excess of two solar masses, albeit somewhat smaller than those obtained with simple extrapolations of the nuclear matter EOSs. Our calculation predicts that no quark matter exists inside neutron stars.

Neutron-Star Radius from a Population of Binary Neutron Star Mergers.

PubMed

Bose, Sukanta; Chakravarti, Kabir; Rezzolla, Luciano; Sathyaprakash, B S; Takami, Kentaro

2018-01-19

We show how gravitational-wave observations with advanced detectors of tens to several tens of neutron-star binaries can measure the neutron-star radius with an accuracy of several to a few percent, for mass and spatial distributions that are realistic, and with none of the sources located within 100 Mpc. We achieve such an accuracy by combining measurements of the total mass from the inspiral phase with those of the compactness from the postmerger oscillation frequencies. For estimating the measurement errors of these frequencies, we utilize analytical fits to postmerger numerical relativity waveforms in the time domain, obtained here for the first time, for four nuclear-physics equations of state and a couple of values for the mass. We further exploit quasiuniversal relations to derive errors in compactness from those frequencies. Measuring the average radius to well within 10% is possible for a sample of 100 binaries distributed uniformly in volume between 100 and 300 Mpc, so long as the equation of state is not too soft or the binaries are not too heavy. We also give error estimates for the Einstein Telescope.

A Search for Black Holes and Neutron Stars in the Kepler Field

NASA Astrophysics Data System (ADS)

Orosz, Jerome; Short, Donald; Welsh, William; Windmiller, Gur; Dabney, David

2018-01-01

Black holes and neutron stars represent the final evolutionary stages of the most massive stars. In addition to their use as probes into the evolution of massive stars, black holes and neutron stars are ideal laboratories to test General Relativity in the strong field limit. The number of neutron stars and black holes in the Milky Way is not precisely known, but there are an estimated one billion neutron stars in the galaxy based on the observed numbers of radio pulsars. The number of black holes is about 100 million, based on the behavior of the Initial Mass Function at high stellar masses.All of the known steller-mass black holes (and a fair number of neutron stars) are in ``X-ray binaries'' that were discovered because of their luminous X-ray emission. The requirement to be in an X-ray-emitting binary places a strong observational bias on the discovery of stellar-mass black holes. Thus the 21 known black hole binaries represent only the very uppermost tip of the population iceberg.We have conducted an optical survey using Kepler data designed to uncover black holes and neutron stars in both ``quiescent'' X-ray binaries and ``pre-contact'' X-ray binaries. We discuss how the search was conducted, including how potentially interesting light curves were classified and the how variability types were identified. Although we did not find any convincing candidate neutron star or black hole systems, we did find a few noteworthy binary systems, including two binaries that contain low-mass stars with unusually low albedos.

An extremely primitive star in the Galactic halo.

PubMed

Caffau, Elisabetta; Bonifacio, Piercarlo; François, Patrick; Sbordone, Luca; Monaco, Lorenzo; Spite, Monique; Spite, François; Ludwig, Hans-G; Cayrel, Roger; Zaggia, Simone; Hammer, François; Randich, Sofia; Molaro, Paolo; Hill, Vanessa

2011-08-31

The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium; almost all other elements were subsequently created in stars and supernovae. The mass fraction of elements more massive than helium, Z, is known as 'metallicity'. A number of very metal-poor stars has been found, some of which have a low iron abundance but are rich in carbon, nitrogen and oxygen. For theoretical reasons and because of an observed absence of stars with Z < 1.5 × 10(-5), it has been suggested that low-mass stars cannot form from the primitive interstellar medium until it has been enriched above a critical value of Z, estimated to lie in the range 1.5 × 10(-8) to 1.5 × 10(-6) (ref. 8), although competing theories claiming the contrary do exist. (We use 'low-mass' here to mean a stellar mass of less than 0.8 solar masses, the stars that survive to the present day.) Here we report the chemical composition of a star in the Galactic halo with a very low Z (≤ 6.9 × 10(-7), which is 4.5 × 10(-5) times that of the Sun) and a chemical pattern typical of classical extremely metal-poor stars--that is, without enrichment of carbon, nitrogen and oxygen. This shows that low-mass stars can be formed at very low metallicity, that is, below the critical value of Z. Lithium is not detected, suggesting a low-metallicity extension of the previously observed trend in lithium depletion. Such lithium depletion implies that the stellar material must have experienced temperatures above two million kelvin in its history, given that this is necessary to destroy lithium.

Intermittent behavior of galactic dynamo activities

NASA Technical Reports Server (NTRS)

Ko, C. M.; Parker, E. N.

1989-01-01

Recent observations by Beck and Golla of far-infrared and radio continuum emission from nearby spiral galaxies suggest that the galactic magnetic field strength is connected to the current star formation rate. The role of star formation on the generation of large-scale galactic magnetic field is studied in this paper. Using a simple galactic model, it is shown how the galactic dynamo depends strongly on the turbulent velocity of the interstellar medium. When the star formation efficiency is high, the ISM is churned which in turn amplifies the galactic magnetic field. Between active star formation epochs, the magnetic field is in dormant state and decays at a negligible rate. If density waves trigger star formation, then they also turn on the otherwise dormant dynamo.

The Fate of the Compact Remnant in Neutron Star Mergers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fryer, Chris L.; Belczynski, Krzysztoff; Ramirez-Ruiz, Enrico

Neutron star (binary neutron star and neutron star - black hole) mergers are believed to produce short-duration gamma-ray bursts. They are also believed to be the dominant source of gravitational waves to be detected by the advanced LIGO and the dominant source of the heavy r-process elements in the universe. Whether or not these mergers produce short-duration GRBs depends sensitively on the fate of the core of the remnant (whether, and how quickly, it forms a black hole). In this paper, we combine the results of merger calculations and equation of state studies to determine the fate of the coresmore » of neutron star mergers. Using population studies, we can determine the distribution of these fates to compare to observations. We find that black hole cores form quickly only for equations of state that predict maximum non-rotating neutron star masses below 2.3-2.4 solar masses. If quick black hole formation is essential in producing gamma-ray bursts, LIGO observed rates compared to GRB rates could be used to constrain the equation of state for dense nuclear matter.« less

The Fate of the Compact Remnant in Neutron Star Mergers

DOE PAGES

Fryer, Chris L.; Belczynski, Krzysztoff; Ramirez-Ruiz, Enrico; ...

2015-10-06

Neutron star (binary neutron star and neutron star - black hole) mergers are believed to produce short-duration gamma-ray bursts. They are also believed to be the dominant source of gravitational waves to be detected by the advanced LIGO and the dominant source of the heavy r-process elements in the universe. Whether or not these mergers produce short-duration GRBs depends sensitively on the fate of the core of the remnant (whether, and how quickly, it forms a black hole). In this paper, we combine the results of merger calculations and equation of state studies to determine the fate of the coresmore » of neutron star mergers. Using population studies, we can determine the distribution of these fates to compare to observations. We find that black hole cores form quickly only for equations of state that predict maximum non-rotating neutron star masses below 2.3-2.4 solar masses. If quick black hole formation is essential in producing gamma-ray bursts, LIGO observed rates compared to GRB rates could be used to constrain the equation of state for dense nuclear matter.« less

The suppression of star formation by powerful active galactic nuclei.

PubMed

Page, M J; Symeonidis, M; Vieira, J D; Altieri, B; Amblard, A; Arumugam, V; Aussel, H; Babbedge, T; Blain, A; Bock, J; Boselli, A; Buat, V; Castro-Rodríguez, N; Cava, A; Chanial, P; Clements, D L; Conley, A; Conversi, L; Cooray, A; Dowell, C D; Dubois, E N; Dunlop, J S; Dwek, E; Dye, S; Eales, S; Elbaz, D; Farrah, D; Fox, M; Franceschini, A; Gear, W; Glenn, J; Griffin, M; Halpern, M; Hatziminaoglou, E; Ibar, E; Isaak, K; Ivison, R J; Lagache, G; Levenson, L; Lu, N; Madden, S; Maffei, B; Mainetti, G; Marchetti, L; Nguyen, H T; O'Halloran, B; Oliver, S J; Omont, A; Panuzzo, P; Papageorgiou, A; Pearson, C P; Pérez-Fournon, I; Pohlen, M; Rawlings, J I; Rigopoulou, D; Riguccini, L; Rizzo, D; Rodighiero, G; Roseboom, I G; Rowan-Robinson, M; Sánchez Portal, M; Schulz, B; Scott, D; Seymour, N; Shupe, D L; Smith, A J; Stevens, J A; Trichas, M; Tugwell, K E; Vaccari, M; Valtchanov, I; Viero, M; Vigroux, L; Wang, L; Ward, R; Wright, G; Xu, C K; Zemcov, M

2012-05-09

The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.

Galactic Halo Stars in Phase Space: A Hint of Satellite Accretion?

NASA Astrophysics Data System (ADS)

Brook, Chris B.; Kawata, Daisuke; Gibson, Brad K.; Flynn, Chris

2003-03-01

The present-day chemical and dynamical properties of the Milky Way bear the imprint of the Galaxy's formation and evolutionary history. One of the most enduring and critical debates surrounding Galactic evolution is that regarding the competition between ``satellite accretion'' and ``monolithic collapse'' the apparent strong correlation between orbital eccentricity and metallicity of halo stars was originally used as supporting evidence for the latter. While modern-day unbiased samples no longer support the claims for a significant correlation, recent evidence has been presented by Chiba & Beers for the existence of a minor population of high-eccentricity metal-deficient halo stars. It has been suggested that these stars represent the signature of a rapid (if minor) collapse phase in the Galaxy's history. Employing velocity and integrals of motion phase-space projections of these stars, coupled with a series of N-body/smoothed particle hydrodynamic chemodynamical simulations, we suggest that an alternative mechanism for creating such stars may be the recent accretion of a polar orbit dwarf galaxy.

Does mass accretion lead to field decay in neutron stars

NASA Technical Reports Server (NTRS)

Shibazaki, N.; Murakami, T.; Shaham, Jacob; Nomoto, K.

1989-01-01

The recent discovery of cyclotron lines from gamma-ray bursts indicates that the strong magnetic fields of isolated neutron stars might not decay. The possible inverse correlation between the strength of the magnetic field and the mass accreted by the neutron star suggests that mass accretion itself may lead to the decay of the magnetic field. The spin and magnetic field evolution of the neutron star was calculated under the hypothesis of the accretion-induced field decay. It is shown that the calculated results are consistent with the observations of binary and millisecond radio pulsars.

Gamma-ray burst constraints on the galactic frequency of extrasolar Oort Clouds

NASA Technical Reports Server (NTRS)

Shull, J. Michael; Stern, S. Alan

1995-01-01

With the strong Compton Gamma-Ray Observatory/Burst and Transient Source Experiment (CGRO/BATSE) evidence that most gamma-ray bursts do not come from galactic neutron stars, models involving the accretion of a comet onto a neutron star (NS) no longer appear to be strong contenders for explaining the majority of bursts. If this is the case, then it is worth asking whether the lack of an observed galactic gamma-ray burst population provides a useful constraint on the number of comets and comet clouds in the galaxy. Owing to the previously unrecognized structural weakness of cometary nuclei, we find the capture cross sections for comet-NS events to be much higher than previously published estimates, with tidal breakup at distances R(sub b) approx. equals 4 x 10(exp 10) cm from the NS. As a result, impacts of comets onto field NSs penetrating the Oort Clouds of other stars are found to dominate all other galactic NS-comet capture rates by a factor of 100. This in turn predicts that if comet clouds are common, there should be a significant population of repeater sources with (1) a galactic distribution, (2) space-correlated repetition, and (3) a wide range of peak luminosities and luminosity time histories. If all main sequence stars have Oort Clouds like our own, we predict approximately 4000 such repeater sources in the Milky Way at any time, each repeating on time scales of months to years. Based on estimates of the sensitivity of the CGRO/BATSE instrument and assuming isotropic gamma-ray beaming from such events, we estimate that a population of approximately 20-200 of these galactic NS-Oort Cloud gamma-ray repeater sources should be detectable by CGRO. In addition, if giant planet formation is common in the galaxy, we estimate that the accretion of isolated comets injected to the interstellar medium by giant planet formation should produce an additional source of galactic, nonrepeating, events. Comparing these estimates to the 3-4 soft gamma-ray repeater sources

Intermediate-mass Elements in Young Supernova Remnants Reveal Neutron Star Kicks by Asymmetric Explosions

NASA Astrophysics Data System (ADS)

Katsuda, Satoru; Morii, Mikio; Janka, Hans-Thomas; Wongwathanarat, Annop; Nakamura, Ko; Kotake, Kei; Mori, Koji; Müller, Ewald; Takiwaki, Tomoya; Tanaka, Masaomi; Tominaga, Nozomu; Tsunemi, Hiroshi

2018-03-01

The birth properties of neutron stars (NSs) yield important information about the still-debated physical processes that trigger the explosion as well as on intrinsic neutron-star physics. These properties include the high space velocities of young neutron stars with average values of several 100 km s‑1, with an underlying “kick” mechanism that is not fully clarified. There are two competing possibilities that could accelerate NSs during their birth: anisotropic ejection of either stellar debris or neutrinos. Here we present new evidence from X-ray measurements that chemical elements between silicon and calcium in six young gaseous supernova remnants are preferentially expelled opposite to the direction of neutron star motion. There is no correlation between the kick velocities and magnetic field strengths of these neutron stars. Our results support a hydrodynamic origin of neutron-star kicks connected to asymmetric explosive mass ejection, and they conflict with neutron-star acceleration scenarios that invoke anisotropic neutrino emission caused by particle and nuclear physics in combination with very strong neutron-star magnetic fields.

Constructing neutron stars with a gravitational Higgs mechanism

NASA Astrophysics Data System (ADS)

Franchini, Nicola; Coates, Andrew; Sotiriou, Thomas P.

2018-03-01

In scalar-tensor theories, spontaneous scalarization is a phase transition that can occur in ultradense environments such as neutron stars. The scalar field develops a nontrivial configuration once the stars exceeds a compactness threshold. We recently pointed out that, if the scalar exhibits some additional coupling to matter, it could give rise to significantly different microphysics in these environments. In this work we study, at the nonperturbative level, a toy model in which the photon is given a large mass when spontaneous scalarization occurs. Our results demonstrate clearly the effectiveness of spontaneous scalarization as a Higgs-like mechanism in neutron stars.

Global Infrared–Radio Spectral Energy Distributions of Galactic Massive Star-Forming Regions

NASA Astrophysics Data System (ADS)

Povich, Matthew Samuel; Binder, Breanna Arlene

2018-01-01

We present a multiwavelength study of 30 Galactic massive star-forming regions. We fit multicomponent dust, blackbody, and power-law continuum models to 3.6 µm through 10 mm spectral energy distributions obtained from Spitzer, MSX, IRAS, Herschel, and Planck archival survey data. Averaged across our sample, ~20% of Lyman continuum photons emitted by massive stars are absorbed by dust before contributing to the ionization of H II regions, while ~50% of the stellar bolometric luminosity is absorbed and reprocessed by dust in the H II regions and surrounding photodissociation regions. The most luminous, infrared-bright regions that fully sample the upper stellar initial mass function (ionizing photon rates NC ≥ 1050 s–1 and total infrared luminosity LTIR ≥ 106.8 L⊙) have higher percentages of absorbed Lyman continuum photons (~40%) and dust-reprocessed starlight (~80%). The monochromatic 70-µm luminosity L70 is linearly correlated with LTIR, and on average L70/LTIR = 50%, in good agreement with extragalactic studies. Calibrated against the known massive stellar content in our sampled H II regions, we find that star formation rates based on L70 are in reasonably good agreement with extragalactic calibrations, when corrected for the smaller physical sizes of the Galactic regions. We caution that absorption of Lyman continuum photons prior to contributing to the observed ionizing photon rate may reduce the attenuation-corrected Hα emission, systematically biasing extragalactic calibrations toward lower star formation rates when applied to spatially-resolved studies of obscured star formation.This work was supported by the National Science Foundation under award CAREER-1454333.

Neutron Stars Rip Each Other Apart to Form Black Hole

NASA Image and Video Library

2014-05-13

This supercomputer simulation shows one of the most violent events in the universe: a pair of neutron stars colliding, merging and forming a black hole. A neutron star is the compressed core left behind when a star born with between eight and 30 times the sun's mass explodes as a supernova. Neutron stars pack about 1.5 times the mass of the sun — equivalent to about half a million Earths — into a ball just 12 miles (20 km) across. As the simulation begins, we view an unequally matched pair of neutron stars weighing 1.4 and 1.7 solar masses. They are separated by only about 11 miles, slightly less distance than their own diameters. Redder colors show regions of progressively lower density. As the stars spiral toward each other, intense tides begin to deform them, possibly cracking their crusts. Neutron stars possess incredible density, but their surfaces are comparatively thin, with densities about a million times greater than gold. Their interiors crush matter to a much greater degree densities rise by 100 million times in their centers. To begin to imagine such mind-boggling densities, consider that a cubic centimeter of neutron star matter outweighs Mount Everest. By 7 milliseconds, tidal forces overwhelm and shatter the lesser star. Its superdense contents erupt into the system and curl a spiral arm of incredibly hot material. At 13 milliseconds, the more massive star has accumulated too much mass to support it against gravity and collapses, and a new black hole is born. The black hole's event horizon — its point of no return — is shown by the gray sphere. While most of the matter from both neutron stars will fall into the black hole, some of the less dense, faster moving matter manages to orbit around it, quickly forming a large and rapidly rotating torus. This torus extends for about 124 miles (200 km) and contains the equivalent of 1/5th the mass of our sun. Scientists think neutron star mergers like this produce short gamma-ray bursts (GRBs). Short

Neutron Stars and the Discovery of Pulsars.

ERIC Educational Resources Information Center

Greenstein, George

1985-01-01

Part one recounted the story of the discovery of pulsars and examined the Crab Nebula, supernovae, and neutron stars. This part (experts from the book "Frozen Star") shows how an understanding of the nature of pulsars allowed astronomers to tie these together. (JN)

Neutron star equation of state and QPO observations

NASA Astrophysics Data System (ADS)

Urbanec, Martin; Stuchlík, Zdeněk; Török, Gabriel; Bakala, Pavel; Čermák, Petr

2007-12-01

Assuming a resonant origin of the twin peak quasiperiodic oscillations observed in the X-ray neutron star binary systems, we apply a genetic algorithm method for selection of neutron star models. It was suggested that pairs of kilohertz peaks in the X-ray Fourier power density spectra of some neutron stars reflect a non-linear resonance between two modes of accretion disk oscillations. We investigate this concept for a specific neutron star source. Each neutron star model is characterized by the equation of state (EOS), rotation frequency Ω and central energy density rho_{c}. These determine the spacetime structure governing geodesic motion and position dependent radial and vertical epicyclic oscillations related to the stable circular geodesics. Particular kinds of resonances (KR) between the oscillations with epicyclic frequencies, or the frequencies derived from them, can take place at special positions assigned ambiguously to the spacetime structure. The pairs of resonant eigenfrequencies relevant to those positions are therefore fully given by KR, rho_{c}, Ω, EOS and can be compared to the observationally determined pairs of eigenfrequencies in order to eliminate the unsatisfactory sets (KR, rho_{c}, Ω, EOS). For the elimination we use the advanced genetic algorithm. Genetic algorithm comes out from the method of natural selection when subjects with the best adaptation to assigned conditions have most chances to survive. The chosen genetic algorithm with sexual reproduction contains one chromosome with restricted lifetime, uniform crossing and genes of type 3/3/5. For encryption of physical description (KR, rho_{c}, Ω, EOS) into the chromosome we use the Gray code. As a fitness function we use correspondence between the observed and calculated pairs of eigenfrequencies.

Chandra Observations of Neutron Stars: An Overview

NASA Technical Reports Server (NTRS)

Weisskopf, Martin C.; Karovska, M.; Pavlov, G. G.; Zavlin, V. E.; Clarke, Tracy

2006-01-01

We present a brief review of Chandra X-ray Observatory observations of neutron stars. The outstanding spatial and spectral resolution of this great observatory have allowed for observations of unprecedented clarity and accuracy. Many of these observations have provided new insights into neutron star physics. We present an admittedly biased and overly brief overview of these observations, highlighting some new discoveries made possible by the Observatory's unique capabilities. We also include our analysis of recent multiwavelength observations of the putative pulsar and its pulsar-wind nebula in the IC 443 SNR.

An instability in neutron stars at birth

NASA Technical Reports Server (NTRS)

Burrows, Adam; Fryxell, Bruce A.

1992-01-01

Calculations with a two-dimensional hydrodynamic simulation show that a generic Raleigh-Taylor-like instability occurs in the mantles of nascent neutron stars, that it is possibly violent, and that the standard spherically symmetric models of neutron star birth and supernova explosion may be inadequate. Whether this 'convective' instability is pivotal to the supernova mechanism, pulsar nagnetic fields, or a host of other important issues that attend stellar collapse remains to be seen, but its existence promises to modify all questions concerning this most energetic of astronomical phenomena.

Why is the rapid burster different from all other galactic-bulge X-ray sources?

NASA Astrophysics Data System (ADS)

Milgrom, M.

1987-01-01

It is suggested that the rapid X-ray burster exhibits unique behavior because it contains a neutron star whose stellar radius is smaller than the minimum radius of a circular orbit that is stable according to general relativity. The star accretes from a disk that extends down to the last stable orbit. In this state, the disk is unstable against a rapid fall and accretion of its innermost part onto the star. The sudden dumping of mass gives rise to a burst of X-rays. The disk then heals, refilling the inner region at a pace that is dictated mainly by the global accretion rate, in order to ready itself for the next burst. In all other galactic-bulge-type sources, the neutron star is larger than the last stable orbit.

NuSTAR and XMM-Newton Observations of 1E1743.1-2843: Indications of a Neutron Star LMXB Nature of the Compact Object

NASA Technical Reports Server (NTRS)

Lotti, Simone; Natalucci, Lorenzo; Mori, Kaya; Baganoff, Frederick K.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Hailey, Charles J.; Harrison, Fiona A.; Hong, Jaesub;

Multimessenger Observations of Neutron Star Mergers: Probing the Physics of High-Density Matter

NASA Astrophysics Data System (ADS)

Radice, David

2016-09-01

Neutron star mergers are Nature's ultimate hadron colliders. They are extremely violent events resulting in gravitational-waves and electromagnetic emissions that could be detected at distances of several hundred mega-parsecs. Imprinted in these signals are important clues on the properties of high-density matter, waiting to be harnessed by us. In this talk, I will review our current knowledge of neutron star mergers from the theoretical side. I will discuss the prospects of measuring neutron star radii and masses using gravitational-wave observations of the late-inspiral of merging neutron stars. Then, I will show how multimessenger observations of the merger and post-merger evolution of merging neutron stars could be used to place further constrains on the nuclear equation of state at very high densities. Finally, I will discuss the possible role of neutron star mergers in the creation of the r-process nuclei in the Universe.

Reassessing the fundamentals: On the evolution, ages and masses of neutron stars

NASA Astrophysics Data System (ADS)

Kiziltan, Bulent

The evolution, ages and masses of neutron stars are the fundamental threads that make pulsars accessible to other sub-disciplines of astronomy and physics. A realistic and accurate determination of these indirectly probed features play an important role in understanding a very broad range of astrophysical processes that are, in many cases, not empirically accessible otherwise. For the majority of pulsars, the only observables are the rotational period (P), and its derivative (P˙) which gives the rate of change in the spin. I start with calculating the joint P-P˙ distributions of millisecond pulsars for the standard evolutionary model in order to assess whether millisecond pulsars are the unequivocal descendants of low mass X-ray binaries. We show that the P-P˙ density implied by the standard evolutionary model is inconsistent with observations, which suggests that it is unlikely that millisecond pulsars have evolved from a single coherent progenitor population. In the absence of constraints from the binary companion or supernova remnant, the standard method for estimating pulsar ages is to infer an age from the rate of spin-down. I parametrically incorporate constraints that arise from binary evolution and limiting physics to derive a "modified spin-down age" for millisecond pulsars. We show that the standard method can be improved by this approach to achieve age estimates closer to the true age. Then, I critically review radio pulsar mass measurements and present a detailed examination through which we are able to put stringent constraints on the underlying neutron star mass distribution. For the first time, we are able to analyze a sizable population of neutron star-white dwarf systems in addition to double neutron star systems with a technique that accounts for systematically different measurement errors. We find that neutron stars that have evolved through different evolutionary paths reflect distinctive signatures through dissimilar distribution peak and

Quasiperiodic oscillations in bright galactic-bulge X-ray sources

NASA Technical Reports Server (NTRS)

Lamb, F. K.; Shibazaki, N.; Alpar, M. A.; Shaham, J.

1985-01-01

Quasiperiodic oscillations with frequencies in the range 5-50 Hz have recently been discovered in X-rays from two bright galactic-bulge sources and Sco X-1. These sources are weakly magnetic neutron stars accreting from disks which the plasma is clumped. The interaction of the magnetosphere with clumps in the inner disk causes oscillations in the X-ray flux with many of the properties observed.

Neutron Stars Rip Each Other Apart to Form Black Hole

NASA Image and Video Library

2014-05-13

Simulation frames from this NASA Goddard neutron star merger animation: bit.ly/1jolBYY Credit: NASA's Goddard Space Flight Center This supercomputer simulation shows one of the most violent events in the universe: a pair of neutron stars colliding, merging and forming a black hole. A neutron star is the compressed core left behind when a star born with between eight and 30 times the sun's mass explodes as a supernova. Neutron stars pack about 1.5 times the mass of the sun — equivalent to about half a million Earths — into a ball just 12 miles (20 km) across. As the simulation begins, we view an unequally matched pair of neutron stars weighing 1.4 and 1.7 solar masses. They are separated by only about 11 miles, slightly less distance than their own diameters. Redder colors show regions of progressively lower density. As the stars spiral toward each other, intense tides begin to deform them, possibly cracking their crusts. Neutron stars possess incredible density, but their surfaces are comparatively thin, with densities about a million times greater than gold. Their interiors crush matter to a much greater degree densities rise by 100 million times in their centers. To begin to imagine such mind-boggling densities, consider that a cubic centimeter of neutron star matter outweighs Mount Everest. By 7 milliseconds, tidal forces overwhelm and shatter the lesser star. Its superdense contents erupt into the system and curl a spiral arm of incredibly hot material. At 13 milliseconds, the more massive star has accumulated too much mass to support it against gravity and collapses, and a new black hole is born. The black hole's event horizon — its point of no return — is shown by the gray sphere. While most of the matter from both neutron stars will fall into the black hole, some of the less dense, faster moving matter manages to orbit around it, quickly forming a large and rapidly rotating torus. This torus extends for about 124 miles (200 km) and contains the

Neutron Stars Rip Each Other Apart to Form Black Hole

NASA Image and Video Library

2017-12-08

Simulation frames from this NASA Goddard neutron star merger animation: bit.ly/1jolBYY Credit: NASA's Goddard Space Flight Center This supercomputer simulation shows one of the most violent events in the universe: a pair of neutron stars colliding, merging and forming a black hole. A neutron star is the compressed core left behind when a star born with between eight and 30 times the sun's mass explodes as a supernova. Neutron stars pack about 1.5 times the mass of the sun — equivalent to about half a million Earths — into a ball just 12 miles (20 km) across. As the simulation begins, we view an unequally matched pair of neutron stars weighing 1.4 and 1.7 solar masses. They are separated by only about 11 miles, slightly less distance than their own diameters. Redder colors show regions of progressively lower density. As the stars spiral toward each other, intense tides begin to deform them, possibly cracking their crusts. Neutron stars possess incredible density, but their surfaces are comparatively thin, with densities about a million times greater than gold. Their interiors crush matter to a much greater degree densities rise by 100 million times in their centers. To begin to imagine such mind-boggling densities, consider that a cubic centimeter of neutron star matter outweighs Mount Everest. By 7 milliseconds, tidal forces overwhelm and shatter the lesser star. Its superdense contents erupt into the system and curl a spiral arm of incredibly hot material. At 13 milliseconds, the more massive star has accumulated too much mass to support it against gravity and collapses, and a new black hole is born. The black hole's event horizon — its point of no return — is shown by the gray sphere. While most of the matter from both neutron stars will fall into the black hole, some of the less dense, faster moving matter manages to orbit around it, quickly forming a large and rapidly rotating torus. This torus extends for about 124 miles (200 km) and contains the

Formation of double neutron star systems as implied by observations

NASA Astrophysics Data System (ADS)

Beniamini, Paz; Piran, Tsvi

2016-03-01

Double Neutron Stars (DNS) have to survive two supernovae (SNe) and still remain bound. This sets strong limits on the nature of the second collapse in these systems. We consider the masses and orbital parameters of the DNS population and constrain the two distributions of mass ejection and kick velocities directly from observations with no a priori assumptions regarding evolutionary models and/or the types of the SNe involved. We show that there is strong evidence for two distinct types of SNe in these systems, where the second collapse in the majority of the observed systems involved small mass ejection (ΔM ≲ 0.5 M⊙) and a corresponding low-kick velocity (vk ≲ 30 km s-1). This formation scenario is compatible, for example, with an electron-capture SN. Only a minority of the systems have formed via the standard SN scenario involving larger mass ejection of ˜2.2 M⊙ and kick velocities of up to 400 km s-1. Due to the typically small kicks in most DNS (which are reflected by rather low proper motion), we predict that most of these systems reside close to the Galactic disc. In particular, this implies that more NS-NS mergers occur close to the Galactic plane. This may have non-trivial implications to the estimated merger rates of DNS and to the rate of LIGO/VIRGO detections.

Search for Hot and Bright Stars for H_3^+ Spectroscopy Near the Galactic Center

NASA Astrophysics Data System (ADS)

Oka, Takeshi; Geballe, T. R.

2009-06-01

It is becoming increasingly clear that H_3^+ is abnormally abundant near the Galactic center and that it is a powerful probe for studying the gas in that region. To date we have observed a dozen sightlines toward bright and hot stars close to the Galactic plane (within 3 pc) and located in the region from the center to 30 pc east of the center. They are mostly stars belonging to the super-massive Quintuplet Cluster and the Central Cluster, but also include few lying between the two clusters. All sightlines showed H_3^+ with column densities on the order of 4 × 10^{15} cm^{-2} demonstrating the ubiquity of H_3^+, its high volume filling factor, and high ionization rate of H_{2} in the region. We plan to expand the region in which we have probed for H_3^+ by two orders of magnitude in solid angle by covering the whole of the Central Molecular Zone (CMZ), the region with a radius of ˜ 200 pc from the center. For this purpose, the first requirement is to find bright and hot stars suitable for the H_3^+ spectroscopy in this more extended region, in which few if any such stars are known outside of the clusters. We are using the recent GLIMPSE Point Source Catalogue provided by the Spitzer Space Telescope together with 2MASS photometry to identify such stars. Out of the over one million stars in GLIMPSE that are in the sightline to the CMZ, we have selected those few thousand stars with L < 7.5 mag. We then use results of J, K, L photometry to eliminate likely late-type stars, whose complex photospheric spectra would make it difficult to isolate the weak interstellar lines of H_3^+. For the few hundred stars thus chosen, we are obtaining medium resolution (R ˜ 2000) spectroscopy from 1.6 to 2.4 μm. The presence or absence of CO overtone bands (2-0, 3-1, 4-2, ...) near 2.3 microns allow us clearly discriminate the hot stars from late-type stars. So far we have observed 84 candidate hot stars and found a dozen that are usable for H_3^+ spectroscopy. Some of them are

Stellar Abundances for Galactic Archaeology Database. IV. Compilation of stars in dwarf galaxies

NASA Astrophysics Data System (ADS)

Suda, Takuma; Hidaka, Jun; Aoki, Wako; Katsuta, Yutaka; Yamada, Shimako; Fujimoto, Masayuki Y.; Ohtani, Yukari; Masuyama, Miyu; Noda, Kazuhiro; Wada, Kentaro

2017-10-01

We have constructed a database of stars in Local Group galaxies using the extended version of the SAGA (Stellar Abundances for Galactic Archaeology) database that contains stars in 24 dwarf spheroidal galaxies and ultra-faint dwarfs. The new version of the database includes more than 4500 stars in the Milky Way, by removing the previous metallicity criterion of [Fe/H] ≤ -2.5, and more than 6000 stars in the Local Group galaxies. We examined the validity of using a combined data set for elemental abundances. We also checked the consistency between the derived distances to individual stars and those to galaxies as given in the literature. Using the updated database, the characteristics of stars in dwarf galaxies are discussed. Our statistical analyses of α-element abundances show that the change of the slope of the [α/Fe] relative to [Fe/H] (so-called "knee") occurs at [Fe/H] = -1.0 ± 0.1 for the Milky Way. The knee positions for selected galaxies are derived by applying the same method. The star formation history of individual galaxies is explored using the slope of the cumulative metallicity distribution function. Radial gradients along the four directions are inspected in six galaxies where we find no direction-dependence of metallicity gradients along the major and minor axes. The compilation of all the available data shows a lack of CEMP-s population in dwarf galaxies, while there may be some CEMP-no stars at [Fe/H] ≲ -3 even in the very small sample. The inspection of the relationship between Eu and Ba abundances confirms an anomalously Ba-rich population in Fornax, which indicates a pre-enrichment of interstellar gas with r-process elements. We do not find any evidence of anti-correlations in O-Na and Mg-Al abundances, which characterizes the abundance trends in the Galactic globular clusters.

An accurate metric for the spacetime around rotating neutron stars

NASA Astrophysics Data System (ADS)

Pappas, George

2017-04-01

The problem of having an accurate description of the spacetime around rotating neutron stars is of great astrophysical interest. For astrophysical applications, one needs to have a metric that captures all the properties of the spacetime around a rotating neutron star. Furthermore, an accurate appropriately parametrized metric, I.e. a metric that is given in terms of parameters that are directly related to the physical structure of the neutron star, could be used to solve the inverse problem, which is to infer the properties of the structure of a neutron star from astrophysical observations. In this work, we present such an approximate stationary and axisymmetric metric for the exterior of rotating neutron stars, which is constructed using the Ernst formalism and is parametrized by the relativistic multipole moments of the central object. This metric is given in terms of an expansion on the Weyl-Papapetrou coordinates with the multipole moments as free parameters and is shown to be extremely accurate in capturing the physical properties of a neutron star spacetime as they are calculated numerically in general relativity. Because the metric is given in terms of an expansion, the expressions are much simpler and easier to implement, in contrast to previous approaches. For the parametrization of the metric in general relativity, the recently discovered universal 3-hair relations are used to produce a three-parameter metric. Finally, a straightforward extension of this metric is given for scalar-tensor theories with a massless scalar field, which also admit a formulation in terms of an Ernst potential.

Baryonic dark clusters in galactic halos and their observable consequences

NASA Technical Reports Server (NTRS)

Wasserman, Ira; Salpeter, Edwin E.

1994-01-01

We consider the possibility that approximately 10% of the mass of a typical galaxy halo is in the form of massive (approximately 10(exp 7) solar masses), compact (escape speeds approximately 100 km/s) baryonic clusters made of neutron stars (approximately 10% by mass), black holes (less than or approximately equal to 1%) and brown dwarfs, asteroids, and other low-mass debris (approximately 90%). These general properties are consistent with several different observational and phenomenological constraints on cluster properties subject to the condition that neutron stars comprise approximately 1% of the total halo mass. Such compact, dark clusters could be the sites of a variety of collisional phenomena involving neutron stars. We find that integrated out to the Hubble distance approximately one neutron star-neutron star or neutron star-black hole collision occurs daily. Of order 0.1-1 asteroid-neutron star collisions may also happen daily in the halo of the Milky Way if there is roughly equal cluster mass per logarithmic particle mass interval between asteroids and brown dwarfs. These event rates are comparable to the frequency of gamma-ray burst detections by the Burst and Transient Source Experiment (BATSE) on the Compton Observatory, implying that if dark halo clusters are the sites of most gamma-ray bursts, perhaps approximately 90% of all bursts are extragalactic, but approximately 10% are galactic. It is possible that dark clusters of the kind discussed here could be detected directly by the Infrared Space Observatory (ISO) or Space Infrared Telescope Facility (SIRTF). If the clusters considered in this paper exist, they should produce spatially correlated gravitational microlensing of stars in the Large Magellanic Cloud (LMC). If 10% of the halo is in the form of dark baryonic clusters, and the remaining 90% is in brown dwarfs and other dark objects which are either unclustered or collected into low-mass clusters, then we expect that two events within

Rapid Neutrino Cooling in the Neutron Star MXB 1659-29.

PubMed

Brown, Edward F; Cumming, Andrew; Fattoyev, Farrukh J; Horowitz, C J; Page, Dany; Reddy, Sanjay

2018-05-04

We show that the neutron star in the transient system MXB 1659-29 has a core neutrino luminosity that substantially exceeds that of the modified Urca reactions (i.e., n+n→n+p+e^{-}+ν[over ¯]_{e} and inverse) and is consistent with the direct Urca (n→p+e^{-}+ν[over ¯]_{e} and inverse) reaction occurring in a small fraction of the core. Observations of the thermal relaxation of the neutron star crust following 2.5 yr of accretion allow us to measure the energy deposited into the core during accretion, which is then reradiated as neutrinos, and infer the core temperature. For a nucleonic core, this requires that the nucleons are unpaired and that the proton fraction exceeds a critical value to allow the direct Urca reaction to proceed. The neutron star in MXB 1659-29 is the first with a firmly detected thermal component in its x-ray spectrum that needs a fast neutrino-cooling process. Measurements of the temperature variation of the neutron star core during quiescence would place an upper limit on the core specific heat and serve as a check on the fraction of the neutron star core in which nucleons are unpaired.

Rapid Neutrino Cooling in the Neutron Star MXB 1659-29

NASA Astrophysics Data System (ADS)

Brown, Edward F.; Cumming, Andrew; Fattoyev, Farrukh J.; Horowitz, C. J.; Page, Dany; Reddy, Sanjay

2018-05-01

We show that the neutron star in the transient system MXB 1659-29 has a core neutrino luminosity that substantially exceeds that of the modified Urca reactions (i.e., n +n →n +p +e-+ν¯ e and inverse) and is consistent with the direct Urca (n →p +e-+ν¯e and inverse) reaction occurring in a small fraction of the core. Observations of the thermal relaxation of the neutron star crust following 2.5 yr of accretion allow us to measure the energy deposited into the core during accretion, which is then reradiated as neutrinos, and infer the core temperature. For a nucleonic core, this requires that the nucleons are unpaired and that the proton fraction exceeds a critical value to allow the direct Urca reaction to proceed. The neutron star in MXB 1659-29 is the first with a firmly detected thermal component in its x-ray spectrum that needs a fast neutrino-cooling process. Measurements of the temperature variation of the neutron star core during quiescence would place an upper limit on the core specific heat and serve as a check on the fraction of the neutron star core in which nucleons are unpaired.

MEASURING NEUTRON STAR RADII VIA PULSE PROFILE MODELING WITH NICER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Özel, Feryal; Psaltis, Dimitrios; Bauböck, Michi

2016-11-20

The Neutron-star Interior Composition Explorer is an X-ray astrophysics payload that will be placed on the International Space Station . Its primary science goal is to measure with high accuracy the pulse profiles that arise from the non-uniform thermal surface emission of rotation-powered pulsars. Modeling general relativistic effects on the profiles will lead to measuring the radii of these neutron stars and to constraining their equation of state. Achieving this goal will depend, among other things, on accurate knowledge of the source, sky, and instrument backgrounds. We use here simple analytic estimates to quantify the level at which these backgroundsmore » need to be known in order for the upcoming measurements to provide significant constraints on the properties of neutron stars. We show that, even in the minimal-information scenario, knowledge of the background at a few percent level for a background-to-source countrate ratio of 0.2 allows for a measurement of the neutron star compactness to better than 10% uncertainty for most of the parameter space. These constraints improve further when more realistic assumptions are made about the neutron star emission and spin, and when additional information about the source itself, such as its mass or distance, are incorporated.« less

A neutron star with a carbon atmosphere in the Cassiopeia A supernova remnant.

PubMed

Ho, Wynn C G; Heinke, Craig O

2009-11-05

The surface of hot neutron stars is covered by a thin atmosphere. If there is accretion after neutron-star formation, the atmosphere could be composed of light elements (H or He); if no accretion takes place or if thermonuclear reactions occur after accretion, heavy elements (for example, Fe) are expected. Despite detailed searches, observations have been unable to confirm the atmospheric composition of isolated neutron stars. Here we report an analysis of archival observations of the compact X-ray source in the centre of the Cassiopeia A supernova remnant. We show that a carbon atmosphere neutron star (with low magnetic field) produces a good fit to the spectrum. Our emission model, in contrast with others, implies an emission size consistent with theoretical predictions for the radius of neutron stars. This result suggests that there is nuclear burning in the surface layers and also identifies the compact source as a very young ( approximately 330-year-old) neutron star.

Neutron star Interior Composition Explorer (NICER)

NASA Image and Video Library

2017-12-08

Optics Lead Takashi Okajima prepares to align NICER’s X-ray optics. The payload’s 56 mirror assemblies concentrate X-rays onto silicon detectors to gather data that will probe the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Neutron star Interior Composition Explorer (NICER)

NASA Image and Video Library

2017-12-08

NICER engineer Steven Kenyon prepares seven of the 56 X-ray concentrators for installation in the NICER instrument. The payload’s 56 mirror assemblies concentrate X-rays onto silicon detectors to gather data that will probe the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Thermal structure and cooling of neutron stars with magnetized envelopes

NASA Astrophysics Data System (ADS)

Potekhin, A. Y.; Yakovlev, D. G.

2001-07-01

The thermal structure of neutron stars with magnetized envelopes is studied using modern physics input. The relation between the internal (Tint) and local surface temperatures is calculated and fitted by analytic expressions for magnetic field strengths B from 0 to 1016 G and arbitrary inclination of the field lines to the surface. The luminosity of a neutron star with dipole magnetic field is calculated and fitted as a function of B, Tint, stellar mass and radius. In addition, we simulate cooling of neutron stars with magnetized envelopes. In particular, we analyse ultramagnetized envelopes of magnetars and also the effects of the magnetic field of the Vela pulsar on the determination of critical temperatures of neutron and proton superfluids in its core.

Equation of State Effects on Binary Neutron Star and Neutron Star-Black Hole Merger Ejecta

NASA Astrophysics Data System (ADS)

Rizzo, Monica; Pankow, Chris; Kalogera, Vassiliki; Coughlin, Scott; Chase, Eve; Imperato, Sam

2018-01-01

Binary neutron stars (BNSs) and neutron star-black hole (NSBH) binaries are not only potential sources of gravitational waves (GWs), but also are thought to generate phenomena such as kilonova, which have proven to be difficult to catch with electromagnetic (EM) instruments. Kilonovae are believed to arise from the radioactive decay of nuclear matter ejected from NSBH and BNS mergers. As they spiral toward each other, neutron stars (NSs), composed of highly dense nuclear matter, are torn apart by their companion's gravity and eject matter. The amount of matter they eject depends sensitively on the composition of NSs, which is described by a nuclear equation of state (EOS). Using fit formulas for ejected mass from Kawaguchi et. al. (2016) and T. Dietrich and M. Ujevic (2016), for NSBH and BNS respectively, we calculate the amount of mass ejected given the initial parameters (masses, black hole spin, etc.) of NSBH and BNS systems. We then predict the distribution of ejected matter for populations of NSBH and BNS mergers, assuming a different EOS for each population. Using formulas derived from The Kilonova Handbook (Metzger, 2016), we can use the calculated ejected mass to generate light curves which, along with GW detections, can be used to place constraints on an EOS for NSs when GW detections are made. We find that the amount of ejected matter observed is distinct for most EOSs, though to draw any solid conclusions about NS composition, joint GW wave and EM counterpart detections are necessary.

Electrically charged: An effective mechanism for soft EOS supporting massive neutron star

NASA Astrophysics Data System (ADS)

Jing, ZhenZhen; Wen, DeHua; Zhang, XiangDong

2015-10-01

The massive neutron star discoverer announced that strange particles, such as hyperons should be ruled out in the neutron star core as the soft Equation of State (EOS) can-not support a massive neutron star. However, many of the nuclear theories and laboratory experiments support that at high density the strange particles will appear and the corresponding EOS of super-dense matters will become soft. This situation promotes a challenge between the astro-observation and nuclear physics. In this work, we introduce an effective mechanism to answer this challenge, that is, if a neutron star is electrically charged, a soft EOS will be equivalently stiffened and thus can support a massive neutron star. By employing a representative soft EOS, it is found that in order to obtain an evident effect on the EOS and thus increasing the maximum stellar mass by the electrostatic field, the total net charge should be in an order of 1020 C. Moreover, by comparing the results of two kind of charge distributions, it is found that even for different distributions, a similar total charge: ~ 2.3 × 1020 C is needed to support a ~ 2.0 M ⊙ neutron star.

Temperature profiles of accretion discs around rapidly rotating strange stars in general relativity: A comparison with neutron stars

NASA Astrophysics Data System (ADS)

Bhattacharyya, S.; Thampan, A. V.; Bombaci, I.

2001-06-01

We compute the temperature profiles of accretion discs around rapidly rotating strange stars, using constant gravitational mass equilibrium sequences of these objects, considering the full effect of general relativity. Beyond a certain critical value of stellar angular momentum (J), we observe the radius (r_orb) of the innermost stable circular orbit (ISCO) to increase with J (a property seen neither in rotating black holes nor in rotating neutron stars). The reason for this is traced to the crucial dependence of dr_orb/dJ on the rate of change of the radial gradient of the Keplerian angular velocity at r_orb with respect to J. The structure parameters and temperature profiles obtained are compared with those of neutron stars, as an attempt to provide signatures for distinguishing between the two. We show that when the full gamut of strange star equation of state models, with varying degrees of stiffness are considered, there exists a substantial overlap in properties of both neutron stars and strange stars. However, applying accretion disc model constraints to rule out stiff strange star equation of state models, we notice that neutron stars and strange stars exclusively occupy certain parameter spaces. This result implies the possibility of distinguishing these objects from each other by sensitive observations through future X-ray detectors.

Gamma-ray burst constraints on the galactic frequency of extra-solar Oort clouds

NASA Technical Reports Server (NTRS)

Shull, J. Michael; Stern, S. Alan

1994-01-01

With the strong CGRO/BATSE evidence that most gamma-ray bursts do not come from galactic neutron stars, models involving the accretion of a comet onto a neutron star (NS) no longer appear to be strong contenders for explaining the majority of bursts. If this is the case, then it is worth asking whether the lack of an observed galactic gamma-ray burst population provides a useful constraint on the number of comets and comet clouds in the galaxy. Owing to the previously unrecognized structural weakness of cometary nuclei, we find the capture cross sections for comet-NS events to be much higher than previously published estimates, with tidal breakup at distances R(sub b) approximately equals to 4 x 10(exp 10) cm from the NS. As a result, impacts of comets onto field NS's penetrating the Oort Clouds of other stars are found to dominate all other galactic NS-comet capture rates by a factor of 100. This in turn predicts that if comet clouds are common, there should be a significant population of repeater sources with (1) a galactic distribution, (2) space-correlated repetition, and (3) a wide range of peak luminosities and luminosity time histories. If all main sequences stars have Oort Clouds like our own, we predict approximately 4000 such repeater sources in the Milky Way at any time, each repeating on timescales of months to years. Based on estimates of the sensitivity of the CGRO/BATSE instrument and assuming isotropic gamma-ray beaming from such events, we estimate that a population of approximately 20-200 of these galactic NS-Oort Cloud gamma-ray repeater sources should be detectable by CGRO. In addition, if giant planet formation is common in the galaxy, we estimate that the accretion of isolated comets injected to the interstellar medium by giant planet formation should produce an additional source of galactic, nonrepeating events. Comparing these estimates to the three to four soft gamma-ray repeater sources detected by BATSE, one is forced to conclude that (1

The Relationship of Sodium and Oxygen in Galactic Field RR Lyrae Stars

NASA Astrophysics Data System (ADS)

Andrievsky, S.; Wallerstein, G.; Korotin, S.; Lyashko, D.; Kovtyukh, V.; Tsymbal, V.; Davis, C. E.; Gomez, T.; Huang, W.; Farrell, E. M.

2018-02-01

We analyzed 62 high-resolution spectra of 30 Galactic Field RR Lyrae-type stars with the aim of deriving their atmospheric parameters (T eff , {log}g, V t ), metallicity ([Fe/H]), radial velocities, and NLTE abundances of oxygen and sodium. We found that there is no clear anti-correlation between [O/Fe] and [Na/Fe] as is seen in globular clusters. On this basis, we conclude that the majority of field RR Lyrae-type stars should hardly be considered to be remnants of the dissolution of globular clusters.

Many-particle theory of nuclear systems with application to neutron star matter

NASA Technical Reports Server (NTRS)

Chakkalakal, D. A.; Yang, C.

1973-01-01

The research is reported concerning energy-density relation for the normal state of neutron star matter, and the effects of superfluidity and polarization on neutron star matter. Considering constraints on variation, and the theory of quantum fluids, three methods for calculating the energy-density range are presented. The effects of polarization on neutron star structure, and polarization effects on condensation and superfluid-state energy are discussed.

Measuring neutron star tidal deformability with Advanced LIGO: A Bayesian analysis of neutron star-black hole binary observations

NASA Astrophysics Data System (ADS)

Kumar, Prayush; Pürrer, Michael; Pfeiffer, Harald P.

2017-02-01

The pioneering discovery of gravitational waves (GWs) by Advanced LIGO has ushered us into an era of observational GW astrophysics. Compact binaries remain the primary target sources for GW observation, of which neutron star-black hole (NSBH) binaries form an important subset. GWs from NSBH sources carry signatures of (a) the tidal distortion of the neutron star by its companion black hole during inspiral, and (b) its potential tidal disruption near merger. In this paper, we present a Bayesian study of the measurability of neutron star tidal deformability ΛNS∝(R /M )NS5 using observation(s) of inspiral-merger GW signals from disruptive NSBH coalescences, taking into account the crucial effect of black hole spins. First, we find that if nontidal templates are used to estimate source parameters for an NSBH signal, the bias introduced in the estimation of nontidal physical parameters will only be significant for loud signals with signal-to-noise ratios greater than ≃30 . For similarly loud signals, we also find that we can begin to put interesting constraints on ΛNS (factor of 1-2) with individual observations. Next, we study how a population of realistic NSBH detections will improve our measurement of neutron star tidal deformability. For an astrophysically likely population of disruptive NSBH coalescences, we find that 20-35 events are sufficient to constrain ΛNS within ±25 %- 50 % , depending on the neutron star equation of state. For these calculations we assume that LIGO will detect black holes with masses within the astrophysical mass gap. In case the mass gap remains preserved in NSBHs detected by LIGO, we estimate that approximately 25% additional detections will furnish comparable ΛNS measurement accuracy. In both cases, we find that it is the loudest 5-10 events that provide most of the tidal information, and not the combination of tens of low-SNR events, thereby facilitating targeted numerical-GR follow-ups of NSBHs. We find these results

NEUTRON STAR MASS–RADIUS CONSTRAINTS USING EVOLUTIONARY OPTIMIZATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stevens, A. L.; Morsink, S. M.; Fiege, J. D.

The equation of state of cold supra-nuclear-density matter, such as in neutron stars, is an open question in astrophysics. A promising method for constraining the neutron star equation of state is modeling pulse profiles of thermonuclear X-ray burst oscillations from hot spots on accreting neutron stars. The pulse profiles, constructed using spherical and oblate neutron star models, are comparable to what would be observed by a next-generation X-ray timing instrument like ASTROSAT , NICER , or a mission similar to LOFT . In this paper, we showcase the use of an evolutionary optimization algorithm to fit pulse profiles to determinemore » the best-fit masses and radii. By fitting synthetic data, we assess how well the optimization algorithm can recover the input parameters. Multiple Poisson realizations of the synthetic pulse profiles, constructed with 1.6 million counts and no background, were fitted with the Ferret algorithm to analyze both statistical and degeneracy-related uncertainty and to explore how the goodness of fit depends on the input parameters. For the regions of parameter space sampled by our tests, the best-determined parameter is the projected velocity of the spot along the observer’s line of sight, with an accuracy of ≤3% compared to the true value and with ≤5% statistical uncertainty. The next best determined are the mass and radius; for a neutron star with a spin frequency of 600 Hz, the best-fit mass and radius are accurate to ≤5%, with respective uncertainties of ≤7% and ≤10%. The accuracy and precision depend on the observer inclination and spot colatitude, with values of ∼1% achievable in mass and radius if both the inclination and colatitude are ≳60°.« less

Probing the internal composition of neutron stars with gravitational waves

NASA Astrophysics Data System (ADS)

Chatziioannou, Katerina; Yagi, Kent; Klein, Antoine; Cornish, Neil; Yunes, Nicolás

2015-11-01

Gravitational waves from neutron star binary inspirals contain information about the as yet unknown equation of state of supranuclear matter. In the absence of definitive experimental evidence that determines the correct equation of state, a number of diverse models that give the pressure inside a neutron star as function of its density have been constructed by nuclear physicists. These models differ not only in the approximations and techniques they employ to solve the many-body Schrödinger equation, but also in the internal neutron star composition they assume. We study whether gravitational wave observations of neutron star binaries in quasicircular inspirals up to contact will allow us to distinguish between equations of state of differing internal composition, thereby providing important information about the properties and behavior of extremely high density matter. We carry out a Bayesian model selection analysis, and find that second generation gravitational wave detectors can heavily constrain equations of state that contain only quark matter, but hybrid stars containing both normal and quark matter are typically harder to distinguish from normal matter stars. A gravitational wave detection with a signal-to-noise ratio of 20 and masses around 1.4 M⊙ would provide indications of the existence or absence of strange quark stars, while a signal-to-noise ratio 30 detection could either detect or rule out strange quark stars with a 20 to 1 confidence. The presence of kaon condensates or hyperons in neutron star inner cores cannot be easily confirmed. For example, for the equations of state studied in this paper, even a gravitational wave signal with a signal-to-noise ratio as high as 60 would not allow us to claim a detection of kaon condensates or hyperons with confidence greater than 5 to 1. On the other hand, if kaon condensates and hyperons do not form in neutron stars, a gravitational wave signal with similar signal-to-noise ratio would be able to

The Suppression of Star Formation by Powerful Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Dwek, E.

2012-01-01

The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight corre1ation between the mass of the black hole and the mas. of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming ga1axies are usually dust-obscured and are brightest at infrared and submillimeter wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(exp 44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expe11ing the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.

SPECTRAL CLASSIFICATION AND PROPERTIES OF THE O Vz STARS IN THE GALACTIC O-STAR SPECTROSCOPIC SURVEY (GOSSS)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arias, Julia I.; Barbá, Rodolfo H.; Sabín-Sanjulián, Carolina

On the basis of the Galactic O Star Spectroscopic Survey (GOSSS), we present a detailed systematic investigation of the O Vz stars. The currently used spectral classification criteria are rediscussed, and the Vz phenomenon is recalibrated through the addition of a quantitative criterion based on the equivalent widths of the He i λ 4471, He ii λ 4542, and He ii λ 4686 spectral lines. The GOSSS O Vz and O V populations resulting from the newly adopted spectral classification criteria are comparatively analyzed. The locations of the O Vz stars are probed, showing a concentration of the most extrememore » cases toward the youngest star-forming regions. The occurrence of the Vz spectral peculiarity in a solar-metallicity environment, as predicted by the fastwind code, is also investigated, confirming the importance of taking into account several processes for the correct interpretation of the phenomenon.« less

Tidal Love numbers of neutron and self-bound quark stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Postnikov, Sergey; Prakash, Madappa; Lattimer, James M.

Gravitational waves from the final stages of inspiraling binary neutron stars are expected to be one of the most important sources for ground-based gravitational wave detectors. The masses of the components are determinable from the orbital and chirp frequencies during the early part of the evolution, and large finite-size (tidal) effects are measurable toward the end of inspiral, but the gravitational wave signal is expected to be very complex at this time. Tidal effects during the early part of the evolution will form a very small correction, but during this phase the signal is relatively clean. The accumulated phase shiftmore » due to tidal corrections is characterized by a single quantity related to a star's tidal Love number. The Love number is sensitive, in particular, to the compactness parameter M/R and the star's internal structure, and its determination could provide an important constraint to the neutron star radius. We show that Love numbers of self-bound strange quark matter stars are qualitatively different from those of normal neutron stars. Observations of the tidal signature from coalescing compact binaries could therefore provide an important, and possibly unique, way to distinguish self-bound strange quark stars from normal neutron stars. Tidal signatures from self-bound strange quark stars with masses smaller than 1M{sub {center_dot}}are substantially smaller than those of normal stars owing to their smaller radii. Thus tidal signatures of stars less massive than 1M{sub {center_dot}}are probably not detectable with Advanced LIGO. For stars with masses in the range 1-2M{sub {center_dot},} the anticipated efficiency of the proposed Einstein telescope would be required for the detection of tidal signatures.« less

A dynamical model for gas flows, star formation and nuclear winds in galactic centres

NASA Astrophysics Data System (ADS)

Krumholz, Mark R.; Kruijssen, J. M. Diederik; Crocker, Roland M.

2017-04-01

We present a dynamical model for gas transport, star formation and winds in the nuclear regions of galaxies, focusing on the Milky Way's Central Molecular Zone (CMZ). In our model angular momentum and mass are transported by a combination of gravitational and bar-driven acoustic instabilities. In gravitationally unstable regions the gas can form stars, and the resulting feedback drives both turbulence and a wind that ejects mass from the CMZ. We show that the CMZ is in a quasi-steady state where mass deposited at large radii by the bar is transported inwards to a star-forming, ring-shaped region at ˜100 pc from the Galactic Centre, where the shear reaches a minimum. This ring undergoes episodic starbursts, with bursts lasting ˜5-10 Myr occurring at ˜20-40 Myr intervals. During quiescence the gas in the ring is not fully cleared, but is driven out of a self-gravitating state by the momentum injected by expanding supernova remnants. Starbursts also drive a wind off the star-forming ring, with a time-averaged mass flux comparable to the star formation rate. We show that our model agrees well with the observed properties of the CMZ, and places it near a star formation minimum within the evolutionary cycle. We argue that such cycles of bursty star formation and winds should be ubiquitous in the nuclei of barred spiral galaxies, and show that the resulting distribution of galactic nuclei on the Kennicutt-Schmidt relation is in good agreement with that observed in nearby galaxies.

The Galactic O-Star Spectroscopic Survey. I. Classification System and Bright Northern Stars in the Blue-violet at R ~ 2500

NASA Astrophysics Data System (ADS)

Sota, A.; Maíz Apellániz, J.; Walborn, N. R.; Alfaro, E. J.; Barbá, R. H.; Morrell, N. I.; Gamen, R. C.; Arias, J. I.

2011-04-01

We present the first installment of a massive spectroscopic survey of Galactic O stars, based on new, high signal-to-noise ratio, R ~ 2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog of Maíz Apellániz et al. and Sota et al. The spectral classification system is rediscussed and a new atlas is presented, which supersedes previous versions. Extensive sequences of exceptional objects are given, including types Ofc, ON/OC, Onfp, Of?p, Oe, and double-lined spectroscopic binaries. The remaining normal spectra bring this first sample to 184 stars, which is close to complete to B = 8 and north of δ = -20° and includes all of the northern objects in Maíz Apellániz et al. that are still classified as O stars. The systematic and random accuracies of these classifications are substantially higher than previously attainable, because of the quality, quantity, and homogeneity of the data and analysis procedures. These results will enhance subsequent investigations in Galactic astronomy and stellar astrophysics. In the future, we will publish the rest of the survey, beginning with a second paper that will include most of the southern stars in Maíz Apellániz et al. The spectroscopic data in this article were gathered with three facilities: the 1.5 m telescope at the Observatorio de Sierra Nevada (OSN), the 3.5 m telescope at Calar Alto Observatory (CAHA), and the du Pont 2.5 m telescope at Las Campanas Observatory (LCO). Some of the supporting imaging data were obtained with the 2.2 m telescope at CAHA and the NASA/ESA Hubble Space Telescope (HST). The rest were retrieved from the DSS2 and Two Micron All Sky Survey (2MASS) surveys. The HST data were obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Variable stars in the Galactic center, as revealed by the VVV Survey

NASA Astrophysics Data System (ADS)

Molina, Claudio Navarro; Borissova, Jura; Catelan, Márcio; Kurtev, Radostin; Medina, Nicolás

2017-09-01

A variability search has been performed in the Galactic center, using the nearinfrared images from the Vista Variables in the Vía Láctea (VVV) Survey. Light curves contain 89 epochs in the KS band. A total of 353 variable stars were found, of which only 47 are already present in the literature.

Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane

NASA Astrophysics Data System (ADS)

Meyer, D. M.-A.; Mackey, J.; Langer, N.; Gvaramadze, V. V.; Mignone, A.; Izzard, R. G.; Kaper, L.

2014-11-01

At least 5 per cent of the massive stars are moving supersonically through the interstellar medium (ISM) and are expected to produce a stellar wind bow shock. We explore how the mass-loss and space velocity of massive runaway stars affect the morphology of their bow shocks. We run two-dimensional axisymmetric hydrodynamical simulations following the evolution of the circumstellar medium of these stars in the Galactic plane from the main sequence to the red supergiant phase. We find that thermal conduction is an important process governing the shape, size and structure of the bow shocks around hot stars, and that they have an optical luminosity mainly produced by forbidden lines, e.g. [O III]. The Hα emission of the bow shocks around hot stars originates from near their contact discontinuity. The Hα emission of bow shocks around cool stars originates from their forward shock, and is too faint to be observed for the bow shocks that we simulate. The emission of optically thin radiation mainly comes from the shocked ISM material. All bow shock models are brighter in the infrared, i.e. the infrared is the most appropriate waveband to search for bow shocks. Our study suggests that the infrared emission comes from near the contact discontinuity for bow shocks of hot stars and from the inner region of shocked wind for bow shocks around cool stars. We predict that, in the Galactic plane, the brightest, i.e. the most easily detectable bow shocks are produced by high-mass stars moving with small space velocities.

Early Results from NICER Observations of Accreting Neutron Stars

NASA Astrophysics Data System (ADS)

Chakrabarty, Deepto; Ozel, Feryal; Arzoumanian, Zaven; Gendreau, Keith C.; Bult, Peter; Cackett, Ed; Chenevez, Jerome; Fabian, Andy; Guillot, Sebastien; Guver, Tolga; Homan, Jeroen; Keek, Laurens; Lamb, Frederick; Ludlam, Renee; Mahmoodifar, Simin; Markwardt, Craig B.; Miller, Jon M.; Psaltis, Dimitrios; Strohmayer, Tod E.; Wilson-Hodge, Colleen A.; Wolff, Michael T.

2018-01-01

The Neutron Star Interior Composition Explorer (NICER) offers significant new capabilities for the study of accreting neuton stars relative to previous X-ray missions including large effective area, low background, and greatly improved low-energy response. The NICER Burst and Accretion Working Group has designed a 2 Ms observation program to study a number of phenomena in accreting neutron stars including type-I X-ray bursts, superbursts, accretion-powered pulsations, quasi-periodic oscillations, and accretion disk reflection spectra. We present some early results from the first six months of the NICER mission.

Gravitational-Wave Constraints on the Neutron-Star-Matter Equation of State

NASA Astrophysics Data System (ADS)

Annala, Eemeli; Gorda, Tyler; Kurkela, Aleksi; Vuorinen, Aleksi

2018-04-01

The detection of gravitational waves originating from a neutron-star merger, GW170817, by the LIGO and Virgo Collaborations has recently provided new stringent limits on the tidal deformabilities of the stars involved in the collision. Combining this measurement with the existence of two-solar-mass stars, we generate a generic family of neutron-star-matter equations of state (EOSs) that interpolate between state-of-the-art theoretical results at low and high baryon density. Comparing the results to ones obtained without the tidal-deformability constraint, we witness a dramatic reduction in the family of allowed EOSs. Based on our analysis, we conclude that the maximal radius of a 1.4-solar-mass neutron star is 13.6 km, and that the smallest allowed tidal deformability of a similar-mass star is Λ (1.4 M⊙)=120 .

Superfluid Density of Neutrons in the Inner Crust of Neutron Stars: New Life for Pulsar Glitch Models

NASA Astrophysics Data System (ADS)

Watanabe, Gentaro; Pethick, C. J.

2017-08-01

Calculations of the effects of band structure on the neutron superfluid density in the crust of neutron stars made under the assumption that the effects of pairing are small [N. Chamel, Phys. Rev. C 85, 035801 (2012)] lead to moments of inertia of superfluid neutrons so small that the crust alone is insufficient to account for the magnitude of neutron star glitches. Inspired by earlier work on ultracold atomic gases in an optical lattice, we investigate fermions with attractive interactions in a periodic lattice in the mean-field approximation. The effects of band structure are suppressed when the pairing gap is of order or greater than the strength of the lattice potential. By applying the results to the inner crust of neutron stars, we conclude that the reduction of the neutron superfluid density is considerably less than previously estimated and, consequently, it is premature to rule out models of glitches based on neutron superfluidity in the crust.

Superfluid Density of Neutrons in the Inner Crust of Neutron Stars: New Life for Pulsar Glitch Models.

PubMed

Watanabe, Gentaro; Pethick, C J

2017-08-11

Calculations of the effects of band structure on the neutron superfluid density in the crust of neutron stars made under the assumption that the effects of pairing are small [N. Chamel, Phys. Rev. C 85, 035801 (2012)PRVCAN0556-2813] lead to moments of inertia of superfluid neutrons so small that the crust alone is insufficient to account for the magnitude of neutron star glitches. Inspired by earlier work on ultracold atomic gases in an optical lattice, we investigate fermions with attractive interactions in a periodic lattice in the mean-field approximation. The effects of band structure are suppressed when the pairing gap is of order or greater than the strength of the lattice potential. By applying the results to the inner crust of neutron stars, we conclude that the reduction of the neutron superfluid density is considerably less than previously estimated and, consequently, it is premature to rule out models of glitches based on neutron superfluidity in the crust.

Milky Way Tomography with K and M Dwarf Stars: The Vertical Structure of the Galactic Disk

NASA Astrophysics Data System (ADS)

Ferguson, Deborah; Gardner, Susan; Yanny, Brian

2017-07-01

We use the number density distributions of K and M dwarf stars with vertical height from the Galactic disk, determined using observations from the Sloan Digital Sky Survey, to probe the structure of the Milky Way disk across the survey’s footprint. Using photometric parallax as a distance estimator we analyze a sample of several million disk stars in matching footprints above and below the Galactic plane, and we determine the location and extent of vertical asymmetries in the number counts in a variety of thin- and thick-disk subsamples in regions of some 200 square degrees within 2 kpc in vertical distance from the Galactic disk. These disk asymmetries present wave-like features as previously observed on other scales and at other distances from the Sun. We additionally explore the scale height of the disk and the implied offset of the Sun from the Galactic plane at different locations, noting that the scale height of the disk can differ significantly when measured using stars only above or only below the plane. Moreover, we compare the shape of the number density distribution in the north for different latitude ranges with a fixed range in longitude and find the shape to be sensitive to the selected latitude window. We explain why this may be indicative of a change in stellar populations in the latitude regions compared, possibly allowing access to the systematic metallicity difference between thin- and thick-disk populations through photometry.

Milky Way Tomography with K and M Dwarf Stars: The Vertical Structure of the Galactic Disk

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferguson, Deborah; Gardner, Susan; Yanny, Brian

2017-07-10

We use the number density distributions of K and M dwarf stars with vertical height from the Galactic disk, determined using observations from the Sloan Digital Sky Survey, to probe the structure of the Milky Way disk across the survey’s footprint. Using photometric parallax as a distance estimator we analyze a sample of several million disk stars in matching footprints above and below the Galactic plane, and we determine the location and extent of vertical asymmetries in the number counts in a variety of thin- and thick-disk subsamples in regions of some 200 square degrees within 2 kpc in verticalmore » distance from the Galactic disk. These disk asymmetries present wave-like features as previously observed on other scales and at other distances from the Sun. We additionally explore the scale height of the disk and the implied offset of the Sun from the Galactic plane at different locations, noting that the scale height of the disk can differ significantly when measured using stars only above or only below the plane. Moreover, we compare the shape of the number density distribution in the north for different latitude ranges with a fixed range in longitude and find the shape to be sensitive to the selected latitude window. We explain why this may be indicative of a change in stellar populations in the latitude regions compared, possibly allowing access to the systematic metallicity difference between thin- and thick-disk populations through photometry.« less

Milky Way tomography with K and M dwarf stars: The vertical structure of the galactic disk

DOE PAGES

Ferguson, Deborah; Gardner, Susan; Yanny, Brian

2017-06-02

Here, we use the number density distributions of K and M dwarf stars with vertical height from the Galactic disk, determined using observations from the Sloan Digital Sky Survey (SDSS), to probe the structure of the Milky Way disk across the survey's footprint. Using photometric parallax as a distance estimator we analyze a sample of several million disk stars in matching footprints above and below the Galactic plane, and we determine the location and extent of vertical asymmetries in the number counts in a variety of thin and thick disk subsamples in regions of some 200 square degrees within 2more » kpc in vertical distance from the Galactic disk. These disk asymmetries present wave-like features as previously observed on other scales and distances from the Sun. We additionally explore the scale height of the disk and the implied offset of the Sun from the Galactic plane at different locations, noting that the scale height of the disk can differ significantly when measured using stars only above or only below the plane. Moreover, we compare the shape of the number density distribution in the north for different latitude ranges with a fixed range in longitude and find the shape to be sensitive to the selected latitude window. We explain why this may be indicative of a change in stellar populations in the compared latitude regions, possibly allowing access to the systematic metallicity difference between thin and thick disk populations through photometry.« less

REVIEWS OF TOPICAL PROBLEMS: Cooling of neutron stars and superfluidity in their cores

NASA Astrophysics Data System (ADS)

Yakovlev, Dmitrii G.; Levenfish, Kseniya P.; Shibanov, Yurii A.

1999-08-01

We study the heat capacity and neutrino emission reactions (direct and modified Urca processes, nucleon-nucleon bremsstrahlung, Cooper pairing of nucleons) in the supranuclear density matter of neutron star cores with superfluid neutrons and protons. Various superfluidity types are analysed (singlet-state pairing and two types of triplet-state pairing, without and with gap nodes at the nucleon Fermi surface). The results are used for cooling simulations of isolated neutron stars. Both the standard cooling and the cooling enhanced by the direct Urca process are strongly affected by nucleon superfluidity. Comparison of the cooling theory of isolated neutron stars with observations of their thermal radiation may give stringent constraints on the critical temperatures of the neutron and proton superfluidities in the neutron star cores.

Inferring the post-merger gravitational wave emission from binary neutron star coalescences

NASA Astrophysics Data System (ADS)

Chatziioannou, Katerina; Clark, James Alexander; Bauswein, Andreas; Millhouse, Margaret; Littenberg, Tyson B.; Cornish, Neil

2017-12-01

We present a robust method to characterize the gravitational wave emission from the remnant of a neutron star coalescence. Our approach makes only minimal assumptions about the morphology of the signal and provides a full posterior probability distribution of the underlying waveform. We apply our method on simulated data from a network of advanced ground-based detectors and demonstrate the gravitational wave signal reconstruction. We study the reconstruction quality for different binary configurations and equations of state for the colliding neutron stars. We show how our method can be used to constrain the yet-uncertain equation of state of neutron star matter. The constraints on the equation of state we derive are complementary to measurements of the tidal deformation of the colliding neutron stars during the late inspiral phase. In the case of nondetection of a post-merger signal following a binary neutron star inspiral, we show that we can place upper limits on the energy emitted.

A new class of g-modes in neutron stars

NASA Technical Reports Server (NTRS)

Reisenegger, Andreas; Goldreich, Peter

1992-01-01

Because a neutron star is born hot, its internal composition is close to chemical equilibrium. In the fluid core, this implies that the ratio of the number densities of charged particles (protons and electrons) to neutrons is an increasing function of the mass density. This composition gradient stably stratifies the matter giving rise to a Brunt-Vaisala frequency N of about 500/s. Consequently, a neutron star core provides a cavity that supports gravity modes (g-modes). These g-modes are distinct from those previously identified with the thermal stratification of the surface layers and the chemical stratification of the crust. We compute the lowest-order, quadrupolar, g-modes for cold, Newtonian, neutron star models with M/solar M = 0.581 and M/solar M = 1.405, and show that the crustal and core g-modes have similar periods. We also discuss damping mechanisms and estimate damping rates for the core g-modes. Particular attention is paid to damping due to the emission of gravitational radiation.

Many-particle theory of nuclear systems with application to neutron star matter

NASA Technical Reports Server (NTRS)

Chakkalakal, D. A.; Yang, C. H.

1974-01-01

The energy-density relation was calculated for pure neutron matter in the density range relevant for neutron stars, using four different hard-core potentials. Calculations are also presented of the properties of the superfluid state of the neutron component, along with the superconducting state of the proton component and the effects of polarization in neutron star matter.

A Gamma-Ray Burst Model Via Compressional Heating of Binary Neutron Stars

NASA Astrophysics Data System (ADS)

Salmonson, J. D.; Wilson, J. R.; Mathews, G. J.

1998-12-01

We present a model for gamma-ray bursts based on the compression of neutron stars in close binary systems. General relativistic (GR) simulations of close neutron star binaries have found compression of the neutron stars estimated to produce 1053 ergs of thermal neutrinos on a timescale of seconds. The hot neutron stars will emit neutrino pairs which will partially recombine to form 1051 to 1052 ergs of electron-positron (e^-e^+) pair plasma. GR hydrodynamic computational modeling of the e^-e^+ plasma flow and recombination yield a gamma-ray burst in good agreement with general characteristics (duration ~10 seconds, spectrum peak energy ~100 keV, total energy ~1051 ergs) of many observed gamma-ray bursts.

Using photometrically selected metal-poor stars to study dwarf galaxies and the Galactic stellar halo

NASA Astrophysics Data System (ADS)

Youakim, Kris; Starkenburg, Else; Martin, Nicolas; Pristine Team

2018-06-01

The Pristine survey is a narrow-band photometric survey designed to efficiently search for extremely metal-poor (EMP) stars. In the first three years of the survey, it has demonstrated great efficiency at finding EMP stars, and also great promise for increasing the current, small sample of the most metal-poor stars. The present sky coverage is ~2500 square degrees in the Northern Galactic Halo, including several individual fields targeting dwarf galaxies. By efficiently identifying member stars in the outskirts of known faint dwarf galaxies, the dynamical histories and chemical abundance patterns of these systems can be understood in greater detail. Additionally, with reliable photometric metallicities over a large sky coverage it is possible to perform a large scale clustering analysis in the Milky Way halo, and investigate the characteristic scale of substructure at different metallicities. This can reveal important details about the process of building up the halo through dwarf galaxy accretion, and offer insight into the connection between dwarf galaxies and the Milky Way halo. In this talk I will outline our results on the search for the most pristine stars, with a focus on how we are using this information to advance our understanding of dwarf galaxies and their contribution to the formation of the Galactic stellar halo.

Hard X-ray spectra of neutron stars and black hole candidates

NASA Technical Reports Server (NTRS)

Durouchoux, P.; Mahoney, W.; Clenet, Y.; Ling, J.; Wallyn, P.; Wheaton, W.; Corbet, S.; Chapuis, C.

1997-01-01

The hard X-ray behavior of several X-ray binary systems containing a neutron star or a black hole candidate is analyzed in an attempt to determine the specific signature of these categories of compact objects. Limiting the consideration to two subclasses of neutron stars, Atoll sources and non-pulsating Z sources, it appears that only the Atoll sources have a spectral behavior similar to black holes. It is proposed that Atoll sources are weakly magnetized neutron stars, whereas Z sources are small radius moderate magnetized neutron stars. Large magnetic fields funnel the accreting matter, thus preventing spherical accretion and free fall if the neutron star radius is smaller than the last stable accreting orbit. Weak magnetic fields do not have this effect, and blackbody soft photons from the stellar surface are upscattered on the relativistic infalling matter, leading to excess hard X-rays. This excess is visible in two of the observed Atoll sources and in the spectrum of a black hole candidate. In the case of a Z source, a lack of photons was remarked, providing a possible signature to distinguish between these classes of objects.

Neutron Star Population Dynamics. II. Three-dimensional Space Velocities of Young Pulsars

NASA Astrophysics Data System (ADS)

Cordes, J. M.; Chernoff, David F.

1998-09-01

We use astrometric, distance, and spindown data on pulsars to (1) estimate three-dimensional velocity components, birth distances from the Galactic plane, and ages of individual objects; (2) determine the distribution of space velocities and the scale height of pulsar progenitors; (3) test spindown laws for pulsars; (4) test for correlations between space velocities and other pulsar parameters; and (5) place empirical requirements on mechanisms than can produce high-velocity neutron stars. Our approach incorporates measurement errors, uncertainties in distances, deceleration in the Galactic potential, and differential Galactic rotation. We focus on a sample of proper motion measurements of young (<10 Myr) pulsars whose trajectories may be accurately and simply modeled. This sample of 49 pulsars excludes millisecond pulsars and other objects that may have undergone accretion-driven spinup. We estimate velocity components and birth z distance on a case-by-case basis assuming that the actual age equals the conventional spindown age for a braking index n = 3, no torque decay, and birth periods much shorter than present-day periods. Every sample member could have originated within 0.3 kpc of the Galactic plane while still having reasonable present-day peculiar radial velocities. For the 49 object sample, the scale height of the progenitors is ~0.13 kpc, and the three-dimensional velocities are distributed in two components with characteristic speeds of 175+19-24 km s-1 and 700+300-132 km s-1, representing ~86% and ~14% of the population, respectively. The sample velocities are inconsistent with a single-component Gaussian model and are well described by a two-component Gaussian model but do not require models of additional complexity. From the best-fit distribution, we estimate that about 20% of the known pulsars will escape the Galaxy, assuming an escape speed of 500 km s-1. The best-fit, dual-component model, if augmented by an additional, low-velocity (<50 km s-1

The link between ejected stars, hardening and eccentricity growth of super massive black holes in galactic nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Long; Berczik, Peter; Spurzem, Rainer

2014-01-10

The hierarchical galaxy formation picture suggests that supermassive black holes (SMBHs) observed in galactic nuclei today have grown from coalescence of massive black hole binaries (MBHB) after galaxy merging. Once the components of an MBHB become gravitationally bound, strong three-body encounters between the MBHB and stars dominate its evolution in a 'dry' gas-free environment and change the MBHB's energy and angular momentum (semimajor axis, eccentricity, and orientation). Here we present high-accuracy direct N-body simulations of spherical and axisymmetric (rotating) galactic nuclei with order of 10{sup 6} stars and two MBHs that are initially unbound. We analyze the properties of themore » ejected stars due to slingshot effects from three-body encounters with the MBHB in detail. Previous studies have investigated the eccentricity and energy changes of MBHs using approximate models or Monte Carlo three-body scatterings. We find general agreement with the average results of previous semi-analytic models for spherical galactic nuclei, but our results show a large statistical variation. Our new results show many more phase space details of how the process works, and also show the influence of stellar system rotation on the process. We detect that the angle between the orbital plane of the MBHBs and that of the stellar system (when it rotates) influences the phase-space properties of the ejected stars. We also find that MBHBs tend to switch stars with counter-rotating orbits into corotating orbits during their interactions.« less

The Planck Catalogue of Galactic Cold Clumps : Looking at the early stages of star-formation

NASA Astrophysics Data System (ADS)

Montier, Ludovic

2015-08-01

The Planck satellite has provided an unprecedented view of the submm sky, allowing us to search for the dust emission of Galactic cold sources. Combining Planck-HFI all-sky maps in the high frequency channels with the IRAS map at 100um, we built the Planck catalogue of Galactic Cold Clumps (PGCC, Planck 2015 results XXVIII 2015), counting 13188 sources distributed over the whole sky, and following mainly the Galactic structures at low and intermediate latitudes. This is the first all-sky catalogue of Galactic cold sources obtained with a single instrument at this resolution and sensitivity, which opens a new window on star-formation processes in our Galaxy.I will briefly describe the colour detection method used to extract the Galactic cold sources, i.e., the Cold Core Colour Detection Tool (CoCoCoDeT, Montier et al. 2010), and its application to the Planck data. I will discuss the statistical distribution of the properties of the PGCC sources (in terms of dust temperature, distance, mass, density and luminosity), which illustrates that the PGCC catalogue spans a large variety of environments and objects, from molecular clouds to cold cores, and covers various stages of evolution. The Planck catalogue is a very powerful tool to study the formation and the evolution of prestellar objects and star-forming regions.I will finally present an overview of the Herschel Key Program Galactic Cold Cores (PI. M.Juvela), which allowed us to follow-up about 350 Planck Galactic Cold Clumps, in various stages of evolution and environments. With this program, the nature and the composition of the 5' Planck sources have been revealed at a sub-arcmin resolution, showing very different configurations, such as starless cold cores or multiple Young Stellar objects still embedded in their cold envelope.

Star-disc interaction in galactic nuclei: formation of a central stellar disc

NASA Astrophysics Data System (ADS)

Panamarev, Taras; Shukirgaliyev, Bekdaulet; Meiron, Yohai; Berczik, Peter; Just, Andreas; Spurzem, Rainer; Omarov, Chingis; Vilkoviskij, Emmanuil

2018-05-01

We perform high-resolution direct N-body simulations to study the effect of an accretion disc on stellar dynamics in an active galactic nucleus (AGN). We show that the interaction of the nuclear stellar cluster (NSC) with the gaseous accretion disc (AD) leads to formation of a stellar disc in the central part of the NSC. The accretion of stars from the stellar disc on to the super-massive black hole is balanced by the capture of stars from the NSC into the stellar disc, yielding a stationary density profile. We derive the migration time through the AD to be 3 per cent of the half-mass relaxation time of the NSC. The mass and size of the stellar disc are 0.7 per cent of the mass and 5 per cent of the influence radius of the super-massive black hole. An AD lifetime shorter than the migration time would result in a less massive nuclear stellar disc. The detection of such a stellar disc could point to past activity of the hosting galactic nucleus.

Inhomogeneous galactic chemical evolution of r-process elements

NASA Astrophysics Data System (ADS)

Wehmeyer, Benjamin

2018-01-01

Stars provide a fundamental contribution to the cosmic life cycle. Gas clouds form and collapse to stars, experiencing different evolutionary stages according to their properties like mass and metal content. Small stars like our Sun end their life as planetary nebulae, while more massive stars end their evolution with violent explosions like supernovae or hypernovae, leaving behind either a neutron star or a black hole. These compact objects may also merge, leading to a new ejection of material. Today the origin of the heaviest elements is still matter of debate. The relative contributions of the proposed sources of r-process elements (e.g., Supernovae, Neutron Star Mergers) in the early galaxy as well as in the Sun is one of the main uncertainties. We use the inhomogeneous chemical evolution tool “ICE” [1, 2] to study the role of some of the main parameters of the cosmic life cycle. With ICE's high resolution (≥ 20parsec/cell) runs, we are able to get converged simulations of the inhomogeneities in the early Galactic evolution stages, and of the observed scatter of r-process elements in metal-poor stars [3].[1] B. Wehmeyer, M. Pignatari, F.-K. Thielemann, 2015 MNRAS 452, 1970–1981[2] B. Wehmeyer, M. Pignatari, F.-K. Thielemann, 2016 AIPC 1743, 040009[3] I. Roederer et al., 2010 ApJ 724:975–993

Applications of machine-learning algorithms for infrared colour selection of Galactic Wolf-Rayet stars

NASA Astrophysics Data System (ADS)

Morello, Giuseppe; Morris, P. W.; Van Dyk, S. D.; Marston, A. P.; Mauerhan, J. C.

2018-01-01

We have investigated and applied machine-learning algorithms for infrared colour selection of Galactic Wolf-Rayet (WR) candidates. Objects taken from the Spitzer Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE) catalogue of the infrared objects in the Galactic plane can be classified into different stellar populations based on the colours inferred from their broad-band photometric magnitudes [J, H and Ks from 2 Micron All Sky Survey (2MASS), and the four Spitzer/IRAC bands]. The algorithms tested in this pilot study are variants of the k-nearest neighbours approach, which is ideal for exploratory studies of classification problems where interrelations between variables and classes are complicated. The aims of this study are (1) to provide an automated tool to select reliable WR candidates and potentially other classes of objects, (2) to measure the efficiency of infrared colour selection at performing these tasks and (3) to lay the groundwork for statistically inferring the total number of WR stars in our Galaxy. We report the performance results obtained over a set of known objects and selected candidates for which we have carried out follow-up spectroscopic observations, and confirm the discovery of four new WR stars.

Interstellar Scattering Towards the Galactic Center as Probed by OH/IR Stars

NASA Technical Reports Server (NTRS)

Vanlangevelde, Huib Jan; Frail, Dale A.; Cordes, James M.; Diamond, Philip J.

1992-01-01

Angular broadening measurements are reported of 20 OH/IR stars near the galactic center. This class of sources is known to have bright, intrinsically compact (less than or equal to 20 mas) maser components within their circumstellar shells. VLBA antennas and the VLA were used to perform a MKII spectral line VLBI experiment. The rapid drop in correlated flux with increasing baseline, especially for sources closest to the galactic center, is attributed to interstellar scattering. Angular diameters were measured for 13 of our sources. Lower limits were obtained for the remaining seven. With the data, together with additional data taken from the literature, the distribution was determined of interstellar scattering toward the galactic center. A region was found of pronounced scattering nearly centered on SgrA*. Two interpretations are considered for the enhanced scattering. One hypothesis is that the scattering is due to a clump of enhanced turbulence, such as those that lie along lines of sight to other known objects, that has no physical relationship to the galactic center. The other model considers the location of the enhanced scattering to arise in the galactic center itself. The physical implications of the models yield information on the nature of interstellar scattering.

The nature of donors in ultraluminous X-ray binaries powered by neutron stars

NASA Astrophysics Data System (ADS)

Karino, Shigeyuki

2018-03-01

This study examines the properties of the donor stars of three recently discovered ultraluminous X-ray sources (ULXs) powered by rotating neutron stars. In order to do this, a theoretical relationship was constructed between the X-ray luminosity (LX) and the orbital period (Porb) suitable for ULXs with neutron stars. Using this new LX-Porb relationship, we attempted to determine the currently unknown nature of donor stars in ULXs associated with neutron stars. In particular, from a comparison between the observed properties and the stellar evolution tracks, we suggest that the donor star in the NGC5907 ULX-1 system is a moderately massive star of 6-12 M⊙, just departing from the main sequence phase. The results of our models for the other two ULX systems (M82 X-2 and NGC7793 P-13) are consistent with those in previous studies. Although there are only a few samples, observed ULX systems with neutron stars seem to involve relatively massive donors.

Physical properties of high-mass star-forming clumps in different evolutionary stages from the Bolocam Galactic Plane Survey

NASA Astrophysics Data System (ADS)

Svoboda, Brian; Shirley, Yancy; Rosolowsky, Erik; Dunham, Miranda; Ellsworth-Bowers, Timothy; Ginsburg, Adam

2013-07-01

High mass stars play a key role in the physical and chemical evolution of the interstellar medium, yet the evolutionary sequence for high mass star forming regions is poorly understood. Recent Galactic plane surveys are providing the first systematic view of high-mass star-forming regions in all evolutionary phases across the Milky Way. We present observations of the 22.23 GHz H2O maser transition J(Ka,Kc) = 6(1,6)→5(2,3) transition toward 1398 clumps identified in the Bolocam Galactic Plane Survey using the 100m Green Bank Telescope (GBT). We detect 392 H2O masers, 279 (71%) newly discovered. We show that H2O masers can identify the presence of protostars which were not previously identified by Spitzer/MSX Galactic plane IR surveys: 25% of IR-dark clumps have an H2O maser. We compare the physical properties of the clumps in the Bolocam Galactic Plane Survey (BGPS) with observations of diagnostics of star formation activity: 8 and 24 um YSO candidates, H2O and CH3OH masers, shocked H2, EGOs, and UCHII regions. We identify a sub-sample of 400 clumps with no star formation indicators representing the largest and most robust sample of pre-protocluster candidates from an unbiased survey to date. The different evolutionary stages show strong separations in HCO+ linewidth and integrated intensity, surface mass density, and kinetic temperature. Monte Carlo techniques are applied to distance probability distribution functions (DPDFs) in order to marginalize over the kinematic distance ambiguity and calculate the distribution of derived quantities for clumps in different evolutionary stages. Surface area and dust mass show weak separations above > 2 pc^2 and > 3x10^3 solar masses. An observed breakdown occurs in the size-linewidth relationship with no differentiation by evolutionary stage. Future work includes adding evolutionary indicators (MIPSGAL, HiGal, MMB) and expanding DPDF priors (HI self-absorption, Galactic structure) for more well-resolved KDAs.

Neutron star Interior Composition Explorer (NICER)

NASA Image and Video Library

2017-12-08

NICER’s X-ray concentrator optics are inspected under a black light for dust and foreign object debris that could impair functionality once in space. The payload’s 56 mirror assemblies concentrate X-rays onto silicon detectors to gather data that will probe the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Neutron star Interior Composition Explorer (NICER)

NASA Image and Video Library

2017-12-08

NICER Optics Lead Takashi Okajima makes a fine adjustment to the orientation of one X-ray “concentrator” optic. The 56 optics must point in the same direction in order for NICER to achieve its science goals. The payload’s 56 mirror assemblies concentrate X-rays onto silicon detectors to gather data that will probe the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Approximate universal relations for neutron stars and quark stars

NASA Astrophysics Data System (ADS)

Yagi, Kent; Yunes, Nicolás

2017-04-01

Neutron stars and quark stars are ideal laboratories to study fundamental physics at supra nuclear densities and strong gravitational fields. Astrophysical observables, however, depend strongly on the star's internal structure, which is currently unknown due to uncertainties in the equation of state. Universal relations, however, exist among certain stellar observables that do not depend sensitively on the star's internal structure. One such set of relations is between the star's moment of inertia (I), its tidal Love number (Love) and its quadrupole moment (Q), the so-called I-Love-Q relations. Similar relations hold among the star's multipole moments, which resemble the well-known black hole no-hair theorems. Universal relations break degeneracies among astrophysical observables, leading to a variety of applications: (i) X-ray measurements of the nuclear matter equation of state, (ii) gravitational wave measurements of the intrinsic spin of inspiraling compact objects, and (iii) gravitational and astrophysical tests of General Relativity that are independent of the equation of state. We here review how the universal relations come about and all the applications that have been devised to date.

Two-component Superfluid Hydrodynamics of Neutron Star Cores

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kobyakov, D. N.; Pethick, C. J., E-mail: dmitry.kobyakov@appl.sci-nnov.ru, E-mail: pethick@nbi.dk

2017-02-20

We consider the hydrodynamics of the outer core of a neutron star under conditions when both neutrons and protons are superfluid. Starting from the equation of motion for the phases of the wave functions of the condensates of neutron pairs and proton pairs, we derive the generalization of the Euler equation for a one-component fluid. These equations are supplemented by the conditions for conservation of neutron number and proton number. Of particular interest is the effect of entrainment, the fact that the current of one nucleon species depends on the momenta per nucleon of both condensates. We find that themore » nonlinear terms in the Euler-like equation contain contributions that have not always been taken into account in previous applications of superfluid hydrodynamics. We apply the formalism to determine the frequency of oscillations about a state with stationary condensates and states with a spatially uniform counterflow of neutrons and protons. The velocities of the coupled sound-like modes of neutrons and protons are calculated from properties of uniform neutron star matter evaluated on the basis of chiral effective field theory. We also derive the condition for the two-stream instability to occur.« less

Neutron star radii, universal relations, and the role of prior distributions

DOE PAGES

Steiner, Andrew W.; Lattimer, James M.; Brown, Edward F.

2016-02-02

We investigate constraints on neutron star structure arising from the assumptions that neutron stars have crusts, that recent calculations of pure neutron matter limit the equation of state of neutron star matter near the nuclear saturation density, that the high-density equation of state is limited by causality and the largest high-accuracy neutron star mass measurement, and that general relativity is the correct theory of gravity. We explore the role of prior assumptions by considering two classes of equation of state models. In a first, the intermediate- and high-density behavior of the equation of state is parameterized by piecewise polytropes. Inmore » the second class, the high-density behavior of the equation of state is parameterized by piecewise continuous line segments. The smallest density at which high-density matter appears is varied in order to allow for strong phase transitions above the nuclear saturation density. We critically examine correlations among the pressure of matter, radii, maximum masses, the binding energy, the moment of inertia, and the tidal deformability, paying special attention to the sensitivity of these correlations to prior assumptions about the equation of state. It is possible to constrain the radii of 1.4 solar mass neutron stars to be larger than 10 km, even without consideration of additional astrophysical observations, for example, those from photospheric radius expansion bursts or quiescent low-mass X-ray binaries. We are able to improve the accuracy of known correlations between the moment of inertia and compactness as well as the binding energy and compactness. Furthermore, we also demonstrate the existence of a correlation between the neutron star binding energy and the moment of inertia.« less

Oscillations During Thermonuclear X-ray Bursts: A New Probe of Neutron Stars