How do white dwarfs form?
White dwarfs are what is left over after a star has exhausted all of the fuel it can ignite. The star can then no longer generate energy, and since it no longer has thermal pressure from fusion, it shrinks and heats up. It is stopped from further contraction by what’s known as degeneracy pressure; once it has contracted as far as it can, it simply cools. We’ll talk more about this next week. White dwarfs exist apart from the main sequence simply by virtue of their high temperature and small luminosity (due to small size), which puts them in the lower left corner of the HR diagram.
