What is the X in X-mas?
in astrophysics, a kind of dead and lightless star, 1966.
|black dwarf |
The theoretical celestial object that remains after a white dwarf has used up all of its fuel and cooled off completely to a solid mass of extremely dense, cold carbon. A white dwarf will eventually become a black dwarf unless it has a companion star from which it can take sufficient mass to pass the Chandrasekhar limit and collapse into a neutron star or black hole. No black dwarf has ever been observed. Because the estimated cooling time for a white dwarf is in the trillions of years, it is unlikely that there are many, if any, black dwarfs in our universe, which is only 12 to 18 billion years old. See Note at dwarf star.
|white dwarf |
A small, extremely dense star characterized by high temperature and luminosity. A white dwarf is believed to be in its final stage of evolution, having either used up most of its nuclear fuel in its main-sequence stage, or else moved through a giant stage and shed any remaining fuel in its outer layer as a planetary nebula, leaving only a glowing core. Some 10 percent of all stars in the Milky Way are white dwarfs, but despite their intrinsic luminosity, they are so small that none are visible to the naked eye. See Note at dwarf.