Compact star facts for kids
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In astronomy, the term compact star (sometimes compact object) is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes.
Most compact stars are the endpoints of stellar evolution and are thus often referred to as stellar remnants, the form of the remnant depending primarily on the mass of the star when it formed. These objects are all small in volume for their mass, giving them a very high density. The term compact star is often used when the exact nature of the star is not known, but evidence suggests that it is very massive and has a small radius, thus implying one of the above-mentioned categories. A compact star that is not a black hole may be called a degenerate star.
Contents
Formation
The usual endpoint of stellar evolution is the formation of a compact star.
Most stars will eventually come to a point in their evolution, when the outward radiation pressure from the nuclear fusions in its interior can no longer resist the ever present gravitational forces. When this happens, the star collapses under its own weight and undergoes the process of stellar death. For most stars, this will result in the formation of a very dense and compact stellar remnant, also known as a compact star.
Compact stars have no internal energy production, but will—with the exception of black holes—usually radiate for millions of years with excess heat left from the collapse itself.
According to the most recent understanding, compact stars could also form during the phase separations of the early Universe following the Big Bang. Primordial origins of known compact objects have not been determined with certainty.
Lifetime
Although compact stars may radiate, and thus cool off and lose energy, they do not depend on high temperatures to maintain their structure, as ordinary stars do. Barring external disturbances and baryonic decay, they can persist virtually forever.
Black holes are however generally believed to finally evaporate from Hawking radiation after trillions of years. According to our current standard models of physical cosmology, all stars will eventually evolve into cool and dark compact stars, by the time the Universe enters the so-called degenerate era in a very distant future.
The somewhat wider definition of compact objects often includes smaller solid objects such as planets, asteroids, and comets. There is a remarkable variety of stars and other clumps of hot matter, but all matter in the Universe must eventually end as some form of compact object, according to the theory of thermodynamics.
Images for kids
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The Eskimo Nebula is illuminated by a white dwarf at its center.
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The Crab Nebula is a supernova remnant containing the Crab Pulsar, a neutron star.
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A simulated black hole of ten solar masses, at a distance of 600 km
See also
In Spanish: Estrella compacta para niños
