Astronomers have found one of the hottest white dwarfs ever recorded!
With a temperature of nearly 200,000 kelvins, KPD 0005+5106 is so hot that it has photospheric emission lines in the ultraviolet. That’s never actually been seen before!
Emission lines are common in many astronomical spectra. Planetary nebulae give off a lot of emission lines – in fact, the one around KPD 0005+5106 gives off O VI (ionised oxygen) emission, while other stars have emission lines from photospheric atoms and ions, and occasionally circumstellar emission lines from molecules and crystalline material… But all of those are normally seen in the visible and infrared regions of light. Ultraviolet emission lines from a star’s photosphere are unheard of, because of how hot that star would need to be!
A white dwarf is the collapsed core of a star that was, once upon a time, not unlike The Sun. A tiny remnant of what once was. But to find one this hot means it can’t have been collapsed very long ago.