Stellar Remnants           

Eventually,all stars consume their nuclear fuel and collapse into one of three final states-white dwarf,neutron star,or black hole.

►White dwarfs are extremely small stars with densities greater than any known terrestrial material.It is believed that white dwarfs began life as low-mass or medium-mass stars.As the star ages,it begins to collapse-become a “dwarf-because it no longer produces sufficient radiant heat to counteract the contracting force of its gravity.Although some white dwarfs are no larger than Earth,the mass of such a dwarf can equal 1.4 times that of the Sun.A spoonful of such matter would weigh several tons.As a star contracts into a white dwarf, its surface becomes very hot and very bright.But,without a continuing source of energy,it will slowly become cooler and dimmer.Although none have been observed,the terminal stage of a white dwarf must be a small,cold, nonluminous body called a black dwarf.

A study of white dwarts produced what might at first appear to be a surprising conclusion:the smallest white dwarfs are the most massive,and the largest white dwarfs are the least massive.The explanation for this is that a more massive star has a greater gravitational force,and that greater gravitational force contracts the star into a smaller,more densely packed object than one gets with a less massive star.Thus,the smallest white dwarfs came from the collapse of stars that were larger and more massive than those the large white dwarfs came from.

Extending this idea of larger stars collapsing to smaller stars leads to the prediction that very large stars would collapse to stars even smaller and more massive than white dwarfs.Named neutron stars,these objects are thought to be the remnants of supernova events (the collapse of a large,very massive star).If Earth were to collapse to the density of a neutron star,it would have a diameter equivalent to the length of a football field,and a pea-sized sample of this matter would weigh 100 million tons.This is approximately the density of an atomic nucleus;thus,neutron stars can be thought of as large atomic nuclei.

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