A white dwarf isn’t your typical kind of star. While main sequence stars such as our Sun fuse nuclear material in their cores to keep themselves from collapsing under their own weight, white dwarfs use an effect known as
quantum degeneracy. The quantum nature of electrons means that no two electrons can have the same quantum state. When you try to squeeze electrons into the same state, they exert a degeneracy pressure that keeps the white dwarf from collapsing.
But there is a limit to how much mass a white dwarf can have. Subrahmanyan Chandrasekhar made a detailed calculation of this limit in 1930 and found that if a white dwarf has more mass than about 1.4 Suns, gravity will crush the star into a neutron star or black hole. But the Chandrasekhar limit is based upon a rather simple model. One where the star is in equilibrium and isn’t rotating. Real white dwarfs are more complex, particularly when they undergo collisions.
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