Four double white dwarfs discovered

Astronomers at the Zwicky Transient Center have discovered four new binary stars that dwarf a growing white dwarf star. The findings were reported in an article published on the preprint server arXiv. Observations indicate that the accreting microbinary system is a white dwarf in the process of stable accretion of material from a donor star. Studying the evolution of such systems can help scientists expand their knowledge about the ultimate fate of white dwarf mergers in binary star systems.

The binary systems identified by astronomers are called ZTF20aabowdt, ZTF18acgmwpt, ZTF19abugzba, and ZTF21abbxnbm. Orbit times range from 25.92 to 56.17 minutes. Typically, accreting microbinaries have orbital periods of less than 65 minutes, which means they emit gravitational waves that affect the evolution of their orbits. ZTF20aabowdt, ZTF18acgmwpt, ZTF21abbxnbm show deep eclipse, but ZTF19abugzba’s eclipse depth is 50%. Because the donor is cold and invisible in the near-infrared, accreting ultracompact binaries usually appear blue, but ZTF19abugzba and ZTF21abbxnbm show a redder color.

ZTF21abbxnbm has the longest orbital period of the four binary stars and is unusual in that it produces three superflares in three years. This behavior is characteristic of a helium cataclysm, rather than a typical long-period cataclysm, as is the case with his three other systems. Cataclysmic stars (CVs) are close binary star systems consisting of primordial white dwarf accreted material from a main sequence star. Their brightness increases unevenly several times, then decreases again and pauses.