The Chandrasekhar limit is the maximum mass of a stable white dwarf star.

White dwarfs resist gravitational collapse primarily through electron degeneracy pressure. In the white dwarf model, as the mass of a white dwarf increases, its radius decreases, which means that all the degenerate electrons in its core are squeezed harder. When the mass reaches about 1.4 solar masses, the electrons are squeezed so tightly that the resulting radius is zero. At this limit the electron degeneracy pressure in the star’s core is insufficient to balance the star’s own gravity. This limit is named the Chandrasekhar limit.

The currently accepted value of the limit is about 1.39 solar masses (2.765 × 10^30 kg).

White dwarfs with masses greater than the Chandrasekhar limit are subject to further gravitational collapse, evolving into a different type of stellar remnant, such as a neutron star or black hole. Only those with masses under the limit remain stable as white dwarfs.

Wikipedia article (https://en.wikipedia.org/wiki/Chandrasekhar_limit) gives Chandrasekhar’s equation and also how a more accurate value of the limit than that given by this simple model can be derived.