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A neutron star is a compact star in which the weight of the star is carried by the pressure of free neutrons. It is a so called degenerate star. The neutron is an elementary particle and one of the building blocks of atomic nuclei. Neutrons are electrically neutral (hence the name) and in contrast to protons, can be packed to form extremely large "nuclei", up to several times the mass of the Sun. Neutron stars are the first major astronomical object whose existence was first predicted from theory (1933) and later (1968) found to exist, at first as radio pulsars.
Neutron stars have a mass of the same order as the mass of the Sun. Their size (radius) is of order 10 km, about 70,000 times smaller than the Sun. So a neutron star's mass is packed in a volume 70,000³ or approximately 1014 times smaller than the Sun and the average mass density can be 1014 times higher than the density in the Sun. Such dense matter cannot be produced in the laboratory. Neutron stars are the densest objects known. It is about the density 'inside' an atomic nucleus. Indeed, one could see a neutron star as a giant atomic nucleus, bound by the gravitational force.
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 100,000 km/s, about 1/3 of the velocity of light. Conversely: an object falling onto the surface of a neutron star would impact the star also at 100,000 km/s. To put this in perspective, if an average human were to encounter a neutron star, they would impact with roughly the energy yield of a 100 megaton nuclear explosion.
Neutron stars are one of the few possible endpoints of stellar evolution, therefore sometimes called a dead star. They are formed in a supernova as the collapsed remnant of a massive star (a Type II or Ib supernova) or as the remnant of a collapsing white dwarf in a Type Ia supernova.
Neutron stars are typically about 20To help compare different orders of magnitude this page lists lengths between 10 and 100 km (104 to 105 m). See also lengths of other orders of magnitude. Distances shorter than 10 km 10 km is equal to: 10,000 metres 6. 2 miles 1 mil unit of measure commo kmA kilometre ( American spelling: kilometer (symbol: km is a unit of length equal to 1000 metres. It is approximately equal to 0. 621 miles, 1094 yards or 3281 feet. Slang terms for kilometre include " klick" (or "click") and "kay". Click" is also used for in diameter, have greater than 1.4 times the mass of our Sun (the Chandrasekhar limitThe Chandrasekhar limit is the maximum mass of a white dwarf, and is approximately 3 × 1030 kg, around 1. 44 times the mass of the Sun. The limit was first calculated by and thus named after the Indian physicist Subrahmanyan Chandrasekhar. The heat genera, below which they'd be white dwarfs instead) and less than about 3 times the mass of our Sun (otherwise they'd be black holeThis article is about the astronomical body. For other uses, see Black hole (disambiguation). roche limit. Infalling matter forms an accretion disk, with some of the matter being ejected in highly energetic polar jets. A black hole is a concentration of ms), and spin very rapidly (one revolution can take anything from thirty seconds to a hundredth of a second).
The matter at the surface of a neutron star is composed of ordinary nuclei as well as ionized 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 neutroniumNeutronium is a colloquial and often misused term for an extremely dense phase of matter that occurs in the intense pressure found in the core of neutron stars and is currently not well understood. It is not an accepted term in astrophysics literature for, 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 pionIn particle physics, pion (short for 'pi meson') is the collective name for three subatomic particles discovered in 1947: π0, π+ and π−. Pions are the lightest mesons. Basic properties Pions have zero spin and are composed of first generatis and kaonThe neutral Kaons represent symmetric and antisymmetric mixtures of the quark combinations down-antistrange and antidown-strange. The charged kaons are mesons which have a quark composition of up-antistrange for the positive kaon and antiup-strange for ths 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.