LYNETTE COOK / SCIENCE PHOTO LIBRARY LYNETTE COOK / SCIENCE PHOTO LIBRARY
White dwarf. Artwork of a white dwarf (at upper left), a dying star. White dwarfs weigh no more than 1.4 times the mass of our Sun and occur when stars have insufficient fuel to carry on generating heat through nuclear reactions. Without this heat the star is unable to maintain its size and slowly shrinks, converting its gravitational potential energy into heat and light. This radiates away, causing the star to shrink further until it is about the diameter of the Earth. The star's matter becomes a degenerate gas in which the electrons have been stripped from their atoms and become closely packed. This can resist further shrinking and the star fades to blackness.
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