Characterizing the local space density of double degenerate binary systems is a complementary approach to broad sky surveys of double degenerates to determine the expected rates of white dwarf binary mergers , in particular those that may evolve into other observable phenomena such as extreme helium stars , Am CVn systems , and supernovae Ia .
However , there have been few such systems detected in local space .
We report here the discovery that WDÂ 1242 - 105 , a nearby bright WD , is a double-line spectroscopic binary consisting of two degenerate DA white dwarfs of similar mass and temperature , despite it previously having been spectroscopically characterized as a single degenerate .
Follow-up photometry , spectroscopy , and trigonometric parallax have been obtained in an effort to determine the fundamental parameters of each component of this system .
The binary has a mass ratio of 0.7 and a trigonometric parallax of 25.5Â mas , placing it at a distance of 39Â pc .
The system ’ s total mass is 0.95Â M _ { \odot } and has an orbital period of 2.85 hours , making it the strongest known gravitational wave source ( \log h = -20.78 ) in the mHz regime .
Because of its orbital period and total mass , WDÂ 1242 - 105 is predicted to merge via gravitational radiation on a timescale of 740Â Myr , which will most likely not result in a catastrophic explosion .