Tags: Star.
RX J0806.3+1527 or HM Cancri (sometimes shortened to HM Cnc or J0806 after establishing identity) is an X-ray binary star system about 1600 light-years (490 pc) away. It comprises two dense white dwarfs orbiting each other once every 321.5 seconds at an estimated distance of only 80000 kilometres (50000 mi) apart (about 1/5 the distance between the Earth and the Moon). The two stars orbit each other at speeds in excess of 400 kilometres per second (890000 mph).
