A white dwarf is the remains of a star that has exhausted its nuclear fuel and shed its outer layers. When a white dwarf dies, there are generally two outcomes depending on its mass and if it has a companion star.
If the white dwarf is less than about 1.4 times the mass of the Sun, it will cool down over billions of years and eventually fade into a cold, dark ‘black dwarf’. This process takes a very long time and is theoretical since the universe isn’t old enough for a black dwarf to exist yet.
However, if the white dwarf is part of a binary system and accumulates enough material from its companion star, it can reach a critical mass, leading to a catastrophic explosion known as a Type Ia supernova. During this process, the white dwarf can no longer support its own mass and undergoes a thermonuclear explosion, releasing a tremendous amount of energy and often outshining an entire galaxy for a short period.
In summary, the death of a white dwarf can either lead to a gradual fading into a black dwarf or a spectacular explosion as a supernova, marking the end of its lifecycle.