White dwarfs

The dim companion star to Sirius, known as Sirius B, was found to be a white dwarf, about the mass of the sun but the size of earth and "white hot". Just like a dense atomic nucleus, stars could be extremely dense and small, challenging previous stellar theories such as the Main Sequence.
 Walter Sydney Adams United States 1914 White dwarfs

The dim companion star to Sirius, known as Sirius B, was found to be a white dwarf, about the mass of the sun but the size of earth and "white hot". Just like a dense atomic nucleus, stars could be extremely dense and small, challenging previous stellar theories such as the Main Sequence.