A white dwarf is a solar-mass star at the end of its stellar evolutionary sequence — essentially the core of a star that began life less than eight times the Sun’s mass. Thermal emission is responsible for all of its radiation, as opposed to nuclear fusion reactions, which support the radiation emission in the early stages of stellar life. When a white dwarf is created, it is hot, but because no process is creating more energy, it soon starts to cool and no longer emits significant heat or light, fading out and becoming a black dwarf.

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