Question

What is the temperature of a white dwarf star ?

Answer 1

Hint:When a star, such as the Sun, runs out of nuclear fuel, it becomes a white dwarf. This type of star expels much of its outer material near the end of its nuclear burning cycle, forming a planetary nebula. The star's hot core is all that remains, and it turns into a very hot white dwarf.

Complete answer:
A white dwarf, also known as a degenerate dwarf, is a stellar core remnant composed of electron-degenerate matter. A white dwarf is extremely dense, with a mass comparable to the Sun and a volume comparable to the Earth. The faint luminosity of a white dwarf is due to the absorption of accumulated thermal energy; no fusion occurs in a white dwarf.

When a star with a mass of less than eight solar masses runs out of Hydrogen in its core, mostly Helium core, it collapses and heats up. Helium fusion begins when the core becomes too hot. When the Helium supply runs out, the core is mostly Carbon and Oxygen. The core cannot reach a temperature high enough to initiate carbon fusion. The core collapses into a white dwarf at this stage. Even though fusion isn't happening in a white dwarf, it's still very hot.

Hence,the temperature of white dwarfs ranges from $$6,000K$$ to $$30,000K$$.

Note: The majority of a white dwarf's mass is at nearly the same temperature and hot. Only the opacity of the white dwarf's outer layers to radiation prevents it from cooling too fast. Remember that a white dwarf cools into a black dwarf after several billions of years. The universe isn’t old enough to have happened this yet.