MAXI J1659-152
MAXI J1659-152 is a rapidly rotating black-hole/star system, discovered by NASA’s Swift space telescope on September 25, 2010. On March 19, 2013, ESA’s XMM-Newton space telescope has helped to identify a star and a black hole that orbit each other at the rate of once every 2.4 hours.
The black hole and the star orbit their common center of mass. Because the star is the lighter object, it lies farther from this point and has to "travel around its larger orbit at a breakneck speed of two million kilometers per hour", 500 to 600 km/s, or about 20 times Earth's orbital velocity. The star is the fastest moving star ever seen in an X-ray binary system. On the other hand, the black hole orbits at ‘only’ 150 000 km/h.
The black hole in this compact pairing is at least three times more massive than the Sun, while its red dwarf companion star has a mass only 20% that of the Sun. The pair is separated by roughly a million kilometers - for comparison the distance to the Sun from Earth is about 150 million kilometers.[1]