This cartoon shows what happens to stars that are about the same size as the sun.
As they get older, the star gets bigger and redder and cooler. The outer gas layers of the star blow off in a high speed wind. We can see this gas for a long time from the Earth. It is called a planetary nebula.
The inner part of the star is left behind. We call it a white dwarf. It is very hot and very small compared to a star. Only about the size of the Earth.
But the matter that makes up the white dwarf is like nothing you've ever seen before. If you took a piece of the white dwarf about the size of a marble, it would weigh as much as the largest elephant at the zoo.