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Neutron star
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Radiation from the pulsar PSR B1509-58, a rapidly spinning neutron star, makes nearby gas glow in X-rays (gold, from Chandra) and illuminates the rest of the nebula, here seen in infrared (blue and red, from WISE).
A neutron star is a type of compact star that can result from the gravitational collapse of a massive star after a supernova. Neutron stars are the densest and smallest stars known to exist in the Universe; with a radius of only about 11–11.5 km (7 mi), they can have a mass of about twice that of the Sun.Neutron stars are composed almost entirely of neutrons, which are subatomic particles without net electrical charge and with slightly larger mass than protons. Neutron stars are very hot and are supported against further collapse by quantum degeneracy pressure due to the phenomenon described by the Pauli exclusion principle, which states that no two neutrons (or any other fermionic particles) can occupy the same place and quantum state simultaneously.A neutron star has a mass of at least 1.1 and perhaps up to 3 solar masses (M?), though the highest observed mass is 2.01 M? Neutron stars typically have a surface temperature around ~7005600000000000000?6×105 K. Neutron stars have overall densities of 7017370000000000000?3.7×1017 to 7017590000000000000?5.9×1017 kg/m3 (7014260000000000000?2.6×1014 to 7014409999999999999?4.1×1014 times the density of the Sun), which is comparable to the approximate density of an atomic nucleus of 7017300000000000000?3×1017 kg/m3.The neutron star's density varies from below 7009100000000000000?1×109 kg/m3 in the crust—increasing with depth—to above 7017600000000000000?6×1017 or 7017800000000000000?8×1017 kg/m3 deeper inside (denser than an atomic nucleus). A normal-sized matchbox containing neutron-star material would have a mass of approximately 5 trillion tons or ~1000 km3 of Earth rock.In general, compact stars of less than 1.39 M? (the Chandrasekhar limit) are white dwarfs, whereas compact stars with a mass between 1.4 M? and 3 M? (the Tolman–Oppenheimer–Volkoff limit) should be neutron stars. The maximum observed mass of neutron stars is about 2 M?. The smallest observed mass of a stellar black hole is about 5 M?, though compact stars with more than 10 M? will overcome the neutron degeneracy pressure and gravitational collapse will usually occur to produce a black hole. Between 3 M? and 5 M?, hypothetical intermediate-mass stars such as quark stars and electroweak stars have been proposed, but none have been shown to exist. The equations of state of matter at such high densities are not precisely known because of the theoretical and empirical difficulties.Some neutron stars rotate very rapidly (up to 716 times a second, or approximately 43,000 revolutions per minute) and emit beams of electromagnetic radiation as pulsars. Indeed, the discovery of pulsars in 1967 first suggested that neutron stars exist.Gamma-ray bursts may be produced from rapidly rotating, high-mass stars that collapse to form a neutron star, or from the merger of binary neutron stars. There are thought to be around 100 million neutron stars in the galaxy, but they can only be easily detected in certain instances, such as if they are a pulsar or part of a binary system. Non-rotating and non-accreting neutron stars are virtually undetectable; however, the Hubble Space Telescope has observed one thermally radiating neutron star, called RX J185635-3754.
^ Özel, Feryal; Psaltis, Dimitrios; Narayan, Ramesh; Santos Villarreal, Antonio (September 2012). "On the Mass Distribution and Birth Masses of Neutron Stars". The Astrophysical Journal 757 (1): 13. arXiv:1201.1006. Bibcode:2012ApJ...757...55O. doi:10.1088/0004-637X/757/1/55. Retrieved 14 May 2015.
^ Chamel, N.; Haensel, P.; Zdunik, J.L.; Fantina, A.F. (19 November 2013). "On the Maximum Mass of Neutron Stars" (PDF). International Journal of Modern Physics 1 (28): 1330018. arXiv:1307.3995. Bibcode:2013IJMPE..2230018C. doi:10.1142/S021830131330018X. Retrieved 14 May 2015.
^ Bulent Kiziltan (2011). Reassessing the Fundamentals: On the Evolution, Ages and Masses of Neutron Stars. Universal-Publishers. ISBN 1-61233-765-1.
^ Neutron star mass measurements
^ "Nasa Ask an Astrophysist: Maximum Mass of a Neutron Star".
^ Pawel Haensel; A Y Potekhin; D G Yakovlev (2007). Neutron Stars. Springer. ISBN 0-387-33543-9.
^ "Calculating a Neutron Star's Density". Retrieved 2006-03-11. NB 3 × 1017 kg/m3 is 7014300000000000000?3×1014 g/cm3
^ "Introduction to neutron stars". Retrieved 2007-11-11.
^ , a 10 M? star will collapse into a black hole.
^ Hessels, Jason; Ransom, Scott M.; Stairs, Ingrid H.; Freire, Paulo C. C.; et al. (2006). "A Radio Pulsar Spinning at 716 Hz". Science 311 (5769): 1901–1904. arXiv:astro-ph/0601337. Bibcode:2006Sci...311.1901H. doi:10.1126/science.1123430. PMID 16410486.
^ Naeye, Robert (2006-01-13). "Spinning Pulsar Smashes Record". Sky & Telescope. Retrieved 2008-01-18.
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