Tiny black holes near the galaxy's centre can fling stars out of the Milky Way at break-neck speeds. Previously, only the supermassive black hole there was thought to be able to produce these "hypervelocity" stars. ... predicted in 1988 that the monster black hole at our galaxy's centre should disrupt pairs of stars, capturing one and launching the other out of the galaxy altogether. Since 2004, astronomers have found nine stars travelling at high speed out of our galaxy – all presumably flung there by the giant black hole, which weighs about 3.6 million times the mass of the Sun. But a new study suggests that many of the ejected stars are getting kicked out by a swarm of much smaller black holes at the galaxy's centre. ... The fastest known hypervelocity star is moving at 709 kilometres per second with respect to the galaxy. The star would have been slowed by the galaxy's gravity on its way out, so it must have been moving at about 1200 kilometres per second initially.
Milky Way star black hole