When the stars die, they will become white dwarfs. At first, the sun will expand into a red giant star, which happens five billions of years later. By this time, the inner planets, Mercury, Venus, Earth and Mars will be eaten up by the Sun. After a few million years later, the star will puff off, leaving behind the dead core which is mostly made up of carbon and oxygen. This is called the white dwarf.
The white dwarf which is smaller than the Earth, was the size of United States. It is still dense and hot. A spoonful of the white dwarf material will be as heavy as the car.