Two huge bubbles that emit gamma rays have been found billowing from the center of the Milky Way galaxy, astronomers have announced. The previously unseen structures, detected by NASA's Fermi Gamma-ray Space Telescope, extend 25,000 light-years north and south from the galactic core. For now the source of all that energy is unclear, said study co-author Doug Finkbeiner, an associate professor of astronomy at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA.
The newfound bubbles are made of hot, charged gas that's releasing the same amount of energy as a hundred thousand exploding stars. One possible answer is that the gamma-ray bubbles are evidence of an ancient burst of star formation at the center of the galaxy. If a huge cluster of massive stars formed millions of years ago, the giants could now be dying together, creating an outbreak of supernovae. "Another hypothesis, which is perhaps even more dramatic, is that the [mostly dormant] black hole at the center of the galaxy is active for a little bit," he said.