How many stars does a black hole eat? The answer to this riddle, at least for some supermassive black holes, is one per year. 

New research from JILA astrophysicist Ann-Marie Madigan and colleagues provides an explanation for the unusual way that stars circle the central black holes of certain galaxies. In such galaxies, including the Milky Way’s nearest neighbor, Andromeda, the orbits of the inner stars are elongated like a stretched-out rubber band. Such shapes are the remnants of ancient collisions between two separate galaxies. 

And they may mean dinner, the researchers found. “Eventually, a star reaches its nearest approach to the black hole, and it gets shredded,” Madigan says. In fact, that can happen at a rate of one star per Earth year, or 10,000 times more often than previous estimates suggested.