Compact star..................... 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 at the endpoint of stellar evolution and thus are called stellar remnants; the form of the remnant depends primarily on the mass of the star when it formed. These objects are all small for their mass. 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 possibilities. A compact star which is not a black hole may be called a degenerate star. Compact stars as the endpoint of stellar evolution................ Compact stars form the endpoint of stellar evolution. A star shines and thus loses energy. The loss from the radiating surface is compensated by the production of energy from nuclear fusion in the interior of the star. When a star has exhausted all its energy and undergoes stellar death, the gas pressure of the hot interior can no longer support the weight of the star and the star collapses to a denser state: a compact star. Lifetime........................ Although compact stars may radiate, and thus cool off and lose energy, they do not depend on high temperatures to maintain their pressure. Barring external perturbation or baryon decay, they will persist virtually forever, although black holes are generally believed to finally evaporate from Hawking radiation. Eventually, given enough time (when we enter the so-called degenerate era of the universe), all stars will have evolved into dark, compact stars. A somewhat wider class of compact objects is sometimes defined to contain, as well as compact stars, smaller solid objects such as planets, asteroids, and comets. These compact objects are the only objects in the universe that could exist at low temperatures. There is a remarkable variety of stars and other clumps of matter, but all dense matter in the universe must eventually end in one of only five classes of compact objects.
Posted on: Mon, 02 Sep 2013 16:12:10 +0000
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