At the center of our galaxy lurks a black hole 4 million times as massive as the Sun. As with some 90% of the supermassive black holes in the universe, the one in our galaxy is currently quiet, meaning the rate of accretion of matter onto it is low. But gamma rays recorded by the Large Area Telescope (LAT) aboard NASA’s Fermi Gamma-Ray Space Telescope reveal a faint glow from two giant structures—the so-called Fermi bubbles—that seem to emerge from the galactic center. It is possible to explain the physical origin of the bubbles without recourse to the galaxy’s central black hole. If, however, the Fermi bubbles are related to the black hole, the scientific consensus is that they reveal a signature of past eruptions and may provide clues to help us better understand the energy output of that enigmatic, massive object at the center of the Milky Way.

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