A team of astronomers at the Friedrich Alexander University, Erlangen-Nürnberg (FAU, Germany), lead by Péter Németh, in collaboration with researchers from the California Institute of Technology (Caltech, USA), has discovered a binary star (PB3877) that is moving nearly at the escape velocity of our Galaxy. About two dozen stars escaping from the Galaxy, termed hyper-velocity stars, are known today. While all of them are single stars, PB3877 is the first binary star found to travel at such a high speed. It is widely accepted that hyper-velocity stars are accelerated by the supermassive black hole in the center of our Galaxy. The results of the new study challenge not only this scenario, but pose further questions. The team showed that the star cannot originate from the Galactic Center, and no other mechanism is known that is able to accelerate a wide binary to such a high velocity without disrupting it. Whether the star is bound to the Galaxy or not depends on the amount of dark matter in the Galaxy. The team found that there must be a lot of dark matter to keep the star bound. Otherwise PB3877 could be an intruder that has been born in another galaxy and may or may not leave the Milky Way again. (More...)
