Here's why:
* Red Giant Phase: When a star like our Sun runs out of hydrogen fuel in its core, it expands and cools, becoming a red giant.
* Collapse: Eventually, the core of the red giant collapses under its own gravity. This collapse generates immense heat and pressure.
* White Dwarf Formation: If the star is not massive enough to become a neutron star or a black hole, the core stabilizes as a white dwarf. White dwarfs are incredibly dense, packing the mass of our Sun into a sphere about the size of Earth.
* Dimness: White dwarfs are very faint because they have exhausted their nuclear fuel and are slowly cooling down. They emit mostly white light, hence the name.
So, while white dwarfs start their life as massive stars, they eventually become very small and dim.
