We have discovered a detached pair of white dwarfs ( WDs ) with a 12.75 min orbital period and a 1,315 km s ^ { -1 } radial velocity amplitude .
We measure the full orbital parameters of the system using its light curve , which shows ellipsoidal variations , Doppler boosting , and primary and secondary eclipses .
The primary is a 0.25 M _ { \odot } tidally distorted helium WD , only the second tidally distorted WD known .
The unseen secondary is a 0.55 M _ { \odot } carbon-oxygen WD .
The two WDs will come into contact in 0.9 Myr due to loss of energy and angular momentum via gravitational wave radiation .
Upon contact the systems may merge yielding a rapidly spinning massive WD , form a stable interacting binary , or possibly explode as an underluminous supernova type Ia .
The system currently has a gravitational wave strain of 10 ^ { -22 } , about 10,000 times larger than the Hulse-Taylor pulsar ; this system would be detected by the proposed LISA gravitational wave mission in the first week of operation .
This system ’ s rapid change in orbital period will provide a fundamental test of general relativity .