Compact star

Extremely dense stars

Compact stars, stars with extremely high density, are white dwarfs, neutron stars, black holes, etc Compact celestial body The general name of.

Chinese name: Compact star
Foreign name: Dense star

application area: astronomy
General term: White dwarfs, neutron stars, black holes
Features: Extremely dense stars

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Star Overview

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The main difference between them and normal stars is that there is no nuclear fuel anymore Fusion reaction The thermal pressure is not enough to keep balance with its own gravity, so it collapses into a very small and dense celestial body.

Compact stars are usually Stellar evolution The final form of the end stage and the type of compact star in the evolution of the star mainly depend on the mass of the star. Generally speaking, stars with a mass of 1 to 6 times the mass of the sun will eventually evolve into white dwarfs, accompanied by mass loss, and their shells will be thrown out to form Planetary nebula 。 Stars with a mass of 3 to 8 times the mass of the sun evolve into neutron stars, and stars with a greater mass collapse into black holes.

Compact stars are white dwarfs, neutron stars, black holes, etc Compact celestial body It is a general term for fixed star 。 After the star's nuclear energy is exhausted Gravitational collapse And formed. Compact stars have high average density, small volume and strong surface gravitational field. There are three types of compact stars

Compact star type

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① Degenerate dwarf , such as white dwarf

Its average density is about 10 ^ 5~10 ^ 7g/cm ^ 3, with a radius of several thousand to tens of thousands of kilometers. Such stars rely on the pressure of degenerate electrons to interact with Gravitational equilibrium The maximum mass of degenerate dwarf is about 1.4 Solar mass , called Chandraseka Limit.

② Neutron star

Its average density is about 10 ^ 13~10 ^ 16g/cm ^ 3, and its radius is about 20km. neutron Stars rely on the pressure of degenerate neutrons to balance gravity. The maximum mass of the neutron star is about 3.2 solar masses, called Oppenheimer limit 。 Pulsars are highly rotating magnetic neutron stars.

③ Black hole

The mass of the black hole is unlimited, and the radius is 2GM/c ^ 2, where G is Universal gravitational constant , M is the mass of the black hole, and c is the speed of light. A black hole with a mass like the sun has a radius of only 3 kilometers.

Compact stars are Stellar evolution The end phase of. The final evolution of a star into a compact star depends mainly on its mass.

Primitive origin

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Normal end point Stellar evolution Is to build a compact star. Most of the points will eventually radiate pressure from the nuclear fusion inside them when they evolve to a point where the pressure can no longer resist the eternal gravity. When this happens, the star folds under its own weight Star death 。 For most stars, this will lead to the creation of a very dense remnant of a star, also known as a compact star.

Dense stars do not have internal energy production, but will - except for black holes - typically emit excess heat from the collapse itself for millions of years. According to our recent understanding, we can also create compact stars in phase separation The early universe of big bang 。 It is well known that the original origin of compact celestial bodies has not yet been confirmed.

evolution

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Although small stars radiate, thus cooling down and losing energy, they do not rely on high temperature to maintain their structure, ordinary stars. Unless external interference and Baryon decay They can persist almost forever. black hole But it is generally believed that the evaporation hawking radiation A trillion years later. According to our standard physical model of the universe, all stars will eventually evolve into cool and compact stars, entering the so-called time decay era from the universe in a very distant future.

A slightly wider definition of Compact objects Often includes smaller solid objects such as planet , Asteroids and comet 。 There is a significantly different star and hot matter mass, but all matter in the universe must end eventually, because some form of compact celestial body, according to theoretical thermodynamics.

Compact star

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