A white dwarf is a small, very bright, white star made up of electron-degenerate matter. In other words, the star's matter has separated: the electrons have parted from the atoms. White dwarfs are dense: the mass is about the same as our Sun's, and the volume is about that of our Earth's.
- Sun's mass: about 1.9891 x 10 to the 27th power kilograms -OR-
- 19,891,000,000,000,000,000,000,000,000,000 kilograms -OR-
- 904,100,000,000,000,000,000,0000,000,000 pounds -OR-
- 452,000,000,000,000,000,000,000,000 tons
The earth's mass is much smaller. The sun accounts for 99.86% of the solar system's mass. The earth's mass is 332,900 times smaller than that of the sun:
- 13,577,650,000,000,000,000,000,000 tons
So, maybe a better way to understand this than all these numbers: the density of the white dwarf compresses about 330,000 times the mass into the same volume as of the earth's.
White dwarfs are thought to be the final evolutionary state of all the stars whose mass isn't too high--which is about 97% of the stars in our galaxy. .
HOW A WHITE DWARF IS FORMED
After all the hydrogen of the star has fused (that hydrogen-fusion process is what gives our sun it's light, heat and energy), the star expands to a RED GIANT , which fuses helium to carbon and oxygen in its core. When a red giant has insufficient mass to generate the core temperatures required to fuse carbon and oxygen, an inert and un-fusable mass of carbon and oxygen builds up in the core. After shedding the outer layers in that last glorious burst of color and energy, the RED GIANT's final sunburst leaves behind the remnant of it's former glory, called a WHITE DWARF . The WHITE DWARF is composed of that unfusable core matter of carbon and oxygen. The carbon and oxygen molecules, minus their electrons, form a solid lattice through which their electrons flow.
The material in a white dwarf no longer undergoes fusion; the star is without a source of energy nor is it supported against gravitational collapse with the heat generated by fusion. It's supported only by the pressure of electron degeneracy
A white dwarf is very hot when it's formed. The heat is caused by the collapse of matter as the electrons are separated from the nuclei. This heat eventually, over a very, very long period of time , dissipates. It radiates away, and then the star becomes A COLD BLACK DWARF .
The star doesn't become a neutron star. The mass at the core, composed of the lattice of nuclei still contains the protons, whose positive charge is balanced by the negatively charged electrons flowing through the lattice.
The material is identifiable as carbon and oxygen, or, in some cases, oxygen-neon-magnesium, when the core temperatures are adequate to fuse carbon but not neon.
HOW LONG IS A VERY, VERY, VERY LONG PERIOD OF TIME?
Since no white dwarf can be older than the Universe, then we have to wait and and see. The Universe is approximately 14 billion years old, according to some estimates--but it varies, the oldest estimate is 300 billion years old. Conventional science accepts presently the 14 to 30 billion-year-old estimate. Even the oldest white dwarfs still radiate at temperatures of a few thousand kelvins, and no black dwarfs are thought to exist as yet.