Many things happen to Stars after they die depending on their size. There are Supernovas, Black Holes, Planetary Nebulae, Neutron Stars, Black Dwarfs and White Dwarfs. White Dwarfs, also known as a degenerate star, is a dense ( density equal to that of H2O water times 1 Million) stellar core remnant that is near its end. White Dwarfs are mostly made of electron degenerate matter. Their mass is that near to The Sun. White Dwarfs want to become Neutron Stars, but simply do not have what it takes, the mass, to become a Neutron Star.
White Dwarfs are recognized for their White Color that they illuminate. It gets its color from the emissions of their stored energy. Fusion does not occur in a White Dwarf, i.e. part of why it is also called a Degenerate Star.
No gravity necessary
Most stars dead or alive, are supported against their own gravity via normal gas pressure; not White Dwarfs however. Instead White Dwarfs are supported by the degenerative pressure of their electron gas within their interior. Degeneracy pressure is an increased resistance exercised by electrons making up the gas, this is a result of stellar contraction.
Composition of a White Dwarf
White Dwarf's centers are made of a blend of both the elements Carbon and Oxygen. Around its center is a thin layer of helium; and a fine layer of hydrogen in most situations. Some White Dwarfs with actually have, though this is rare, have a thin carbon envelope.
Where do White dwarfs come from?
A Star that is initially 3 to 4 Solar Masses will become a White Dwarfs. This sometimes can be a higher number but typically the star is 3 to 4 Solar Masses. Stars that can become a White Dwarfs are Sun-Like Stars, Red Giants, Red Dwarfs & Planetary Nebulae. Our Sun will eventually become a White Dwarfs but first The Sun will expand and become a Red Giant. After this it will become a Planetary Nebulae. Over time, the mass of The Sun will wither away and The Planetary Nebula Sun will become a White Dwarf.
Examples of White Dwarfs
A few examples of White Dwarfs Stars are Sirius (The Brightest Star seen on Earth), Sirius A, IK Pegasi, Wolf 489, NN Serpentis, PSR J0348+0432, Procyon B & Lambda Boötis. There are currently believed to be 8 White Dwarfs in space.
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