Hypervelocity Stars Ejected from the Galactic Center

 

A massive black hole in a dense crowd of stars will inevitably eject a few stars completely out of the Galaxy. In 2005 we discovered the first such "hypervelocity star:'' a short-lived star three times the mass of the Sun, very similar to the stars seen in the Galactic Center, but ~110 kpc distant and moving away at over 700 km/s. We have designed a successful survey to find more hypervelocity stars. I will describe our most recent results, including the possible discovery of stars ejected from the Galactic center on bound trajectories. Our hypervelocity stars tell us about the history of stars encountering the central massive back hole, and the types of stars orbiting around it.