What is the difference between a red giant and a white dwarf?

A red giant is a large, luminous star in its final stages of life, while a white dwarf is a small, dense star that has exhausted its nuclear fuel.

Red giants are formed when a star runs out of hydrogen fuel in its core and begins to fuse helium. This causes the outer layers of the star to expand and cool, making it appear red and much larger than before. Red giants can be up to 100 times larger than the original star and can last for millions of years before eventually shedding their outer layers and becoming a white dwarf. The luminosity of red giants, as they expand and cool, is a significant aspect of their stage in the stellar lifecycle, which is discussed in detail on the luminosity concept page.

White dwarfs are the remnants of stars that have exhausted all of their nuclear fuel and have collapsed under their own gravity. They are incredibly dense, with a mass similar to that of the sun but a size comparable to that of Earth. White dwarfs are incredibly hot, with temperatures of up to 100,000 Kelvin, but they are not able to produce energy through nuclear fusion like they did when they were stars. Instead, they slowly cool over billions of years until they become cold, dark objects known as black dwarfs. The electromagnetic radiation emitted by white dwarfs can be better understood by exploring the nature of electromagnetic waves.

In summary, red giants and white dwarfs are two very different stages in the life cycle of a star. Red giants are large, luminous stars in their final stages of life, while white dwarfs are small, dense objects that have exhausted their nuclear fuel and are slowly cooling over billions of years. The transformation from red giants to white dwarfs involves complex nuclear processes, primarily involving the fusion of helium, as outlined on the fusion processes page.