Image Credit: ESO via Flickr
About 2 million years ago the black hole at the center of our galaxy suddenly sprang to life rivaling the moon in the night sky, around the time our ancestors learned to walk. “That is when we had Homo erectus running around Earth,” says Joss Bland-Hawthorn of the University of Sydney, who led the team behind the work. The work was announced a few years ago at a conference in Sydney, which put together and solved 2 seemingly unrelated puzzles.
Black holes get their name due to the fact nothing, including light, can escape it’s gravity, so it seems ironic they can be some of the brightest objects in the Universe. But the centers of galaxies known as active galactic nuclei or AGN, shine brightly. The reason is that as the supermassive black hole pulls matter in, the matter accretes in a surrounding disc, which heats up and starts glowing. When large amounts of matter get pulled into the disc, energy is released as bright jets of particles perpendicular to the black hole’s spin.
The Milky Way’s central black hole, called Sagittarius A*, is currently docile, but no one knows exactly what makes a black hole turn into an AGN. One clue that our galaxy wasn’t always quiet came in 2010, when astronomers using NASA’s Fermi gamma-ray satellite spotted a pair of spectacular but mysterious structures now called the Fermi bubbles, towering 25,000 light years above and below the galactic plane. Theories to explain the bubbles range from gamma rays emitted by annihilating dark matter to supersonic winds unleashed by intense bursts of star formation.
Then in April, at a meeting at Stanford University in California, Bill Mathews and Fulai Guo of the University of California, Santa Cruz, argued that the bubbles were caused by an outburst from Sagittarius A*. Their simulations showed that two intense jets of high-energy particles, like those produced by an AGN, streaming out from the vicinity of the black hole could have created the bubbles. The flare-up, they calculated, would have happened between 1 and 3 million years ago and lasted a few hundred thousand years (arxiv.org/abs/1103.0055v3).
Source: New Scientist
In addition, this outburst seemed to solve another 20 year old longstanding mystery..
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