White Dwarf
White Dwarf (circled)
Courtesy J. Westphal and STSci
They are very hot (up to 100,000 °C) and small, but very dense (they are about the size of the Earth but have as much mass as the Sun!)
They are so dense because they are not made of normal atoms, but of atoms that have been crushed down by gravity.
They are not really stars since they produce no new energy - they are just slowly cooling down.
