STARS plunging into the giant black hole at the centre of our galaxy can explain two huge bubbles of gamma rays that NASA鈥檚 Fermi space telescope discovered last year. The bubbles tower 25,000 light years above and below the Milky Way鈥檚 disc of stars.
More than 100,000 stars swarm within a light year of the black hole. Now, of the University of Hong Kong and his colleagues calculate that the black hole鈥檚 gravity tears one of these stars apart every 30,000 years (, in press). Half the star鈥檚 mass falls into the black hole, while the other half shoots away at high speed, shocking gas that lies in the halo around the Milky Way鈥檚 disc until it emits gamma rays.
However, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, thinks individual stars dribbling into the black hole would probably not produce the sharp edges seen around the Fermi bubbles.
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鈥淭o make a sharp edge, the mechanism really needs to turn on and turn off,鈥� he says. 鈥淢y money is on the explanations that involve something more dramatic and more rare.鈥� He suspects that every 1 million to 10 million years, a huge cloud of gas or an entire cluster of stars plummets into the black hole. The most recent such event, he says, produced the Fermi bubbles we see today.
