White dwarf
The second white dwarf was discovered in 1862, but was at first thought to be a red dwarf. It was a small star near the star Sirius. This companion star, called Sirius B, had a surface temperature of about 25,000 kelvin, so it was thought of as a hot star. However, Sirius B was about 10,000 times fainter than the primary, Sirius A.  Scientists have discovered that the mass of Sirius B is almost the same as that of the Sun. This means that once, Sirius B was a star similar to our own Sun.