Here's why:

* White Dwarfs are the End Stage: White dwarfs are the final stage for stars with a mass similar to or smaller than our Sun. They are incredibly dense, and their nuclear fusion has ceased.

* No Further Fusion: Without fusion, white dwarfs slowly cool and fade, eventually becoming black dwarfs.

* Black Dwarfs: While theoretically possible, black dwarfs are not yet observed because the process of cooling down takes trillions of years, longer than the current age of the universe.

The other terms you mentioned relate to different stages of stellar evolution:

* Red Giant: A stage where a star expands significantly after exhausting hydrogen fuel in its core.

* Prostar: A collapsing cloud of gas and dust before it becomes a true star.

* Neutron Star: A very dense remnant of a massive star after a supernova explosion.

* Black Hole: A region of spacetime where gravity is so strong that nothing, not even light, can escape.

Let me know if you have any more questions about stellar evolution!