That limit, about 1.4 times the mass of the Sun, became known, appropriately, as the Chandrasekhar Limit. Any white dwarf that gains enough mass to exceed that limit is immediately doomed to explode spectacularly as a supernova. And now that we know that the physics of the explosion is always the same, we know how bright a Type Ia supernova is intrinsically, and can therefore figure out its distance.
