Neutron star

:This article is about the celestial body. "Neutron Star" was a 1966 Hugo award winning short story by Larry Niven

Structure

Neutron stars have a typical mass about 1.4 times the mass of the Sun. Their size (radius) is of order 12 km, about 60,000 times smaller than the Sun. So a neutron star's mass is packed in a volume 60,0003; or approximately 2x1014 times smaller than the Sun and the average mass density can be 1014 times higher than the density in the Sun. Such densities have yet to be produced in the laboratory. In fact, the density of a neutron star is about the density of an atomic nucleus.

Related Topics:
Mass - Sun - Radius - Density

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Due to its small size and high density, a neutron star possesses a surface gravitational field about 2×1011 times that of Earth. One of the measures for the gravity is the escape velocity, the velocity one would need to give an object, such that it can escape from the gravitational field into infinity. For a neutron star, such velocities are typically 150,000 km/s, about 1/2 of the velocity of light. Conversely: an object falling onto the surface of a neutron star would impact the star also at 150,000 km/s. To put this in perspective, if an average human were to encounter a neutron star, he or she would impact with roughly the energy yield of a 100 megaton nuclear explosion.

Related Topics:
Gravitational field - Escape velocity - Infinity - 150,000 km/s - Megaton - Nuclear explosion

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Neutron stars are one of the few possible endpoints of stellar evolution. They are formed in a supernova as the collapsed remnant of a massive star (a Type II or Ib/c supernova).

Related Topics:
Stellar evolution - Supernova - Collapsed

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Neutron stars are typically about 25 km in diameter, have greater than 1.4 times the mass of our Sun (the Chandrasekhar limit, below which they'd be white dwarfs instead) and less than about 3 times the mass of our Sun (otherwise they'd be black holes), and spin very rapidly (one revolution can take anything from thirty seconds to one six-hundredth of a second).

Related Topics:
25 - Km - 1.4 times - Chandrasekhar limit - White dwarf - Black hole

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Current understanding of the structure of neutron stars is defined by existing mathematical models, which of course are subject to revision. Based on current models, the matter at the surface of a neutron star is composed of ordinary nuclei as well as electrons. The "atmosphere" of the star is roughly one metre thick, below which one encounters a solid "crust". Proceeding inward, one encounters nuclei with ever increasing numbers of neutrons; such nuclei would quickly decay on Earth, but are kept stable by tremendous pressures. Proceeding deeper, one comes to a point called neutron drip where free neutrons leak out of nuclei. In this region we have nuclei, free electrons, and free neutrons. The nuclei become smaller and smaller until the core is reached, by definition the point where they disappear altogether. The exact nature of the superdense matter in the core is still not well understood. Some researchers refer to this theoretical substance as neutronium, though this term can be misleading and is more frequently used in science fiction. It could be a superfluid mixture of neutrons with a few protons and electrons, other high-energy particles like pions and kaons may be present, and even sub-atomic quark matter is possible. However so far observations have not indicated nor ruled out such exotic states of matter.

Related Topics:
Neutron drip - Neutronium - Pion - Kaon - Quark matter

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