White dwarf binary system found through gravitational microlensing

Ars Technica : Type Ia supernovae are thought to occur in binary systems in which a white dwarf accretes enough material from its stellar companion to set off a thermonuclear explosion. To better understand those supernovae, it is necessary to find binary systems with white dwarfs before the supernovae occur. One such system has just been found, thanks to the gravitational microlensing of the partner star’s light as the white dwarf passed between its partner and Earth. When the lensing is caused by the second member of a binary system, it is known as self-lensing. The system was first identified by the Kepler Space Telescope as a candidate planetary system. Further observations revealed a periodic increase of 0.1% in the brightness of the system’s Sun-like star that occurred every 88 days and lasted 5 hours. That allowed scientists to calculate both the white dwarf’s mass, which is 63% of the Sun’s, and its diameter, which is just 1.1% of the Sun’s and nearly the same as Earth’s. With the partner star still being in the middle of its life, the system is far from becoming a supernova. However, it is likely an example of a common class of binary and should provide valuable information about similar systems.