A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. From Wikipedia
The newly identified system, located 150-160 light-years away, features a 14-hour orbit and a combined mass of 1.56 solar masses, marking it as a future Type Ia supernova candidate.
