Milky Way’s ‘sleeping dragon’ breathed fire 2 million years ago

The supermassive black hole at the centre of the Milky Way galaxy is quiet these days, but researchers have found that in the past it has produced eruptions so powerful that they lit up gas clouds hundreds of thousands of light years away.

Sagittaris A* has long been a slumbering giant, showing so little activity that even though it's the object that binds our galaxy together, we didn't even know it was there until 1974 — long after astronomy was invented. Even then, it was only discovered by watching how it affected nearby stars, as we couldn't actually see the black hole itself. However, a team of researchers has revealed evidence that this slumbering giant is actually more of a sleeping dragon, capable of waking up and letting off incredible blasts of energy that would have made it highly visible.

"For 20 years astronomers have suspected that such a significant outburst occurred, but now we know when this sleeping dragon, four million times the mass of the sun, awoke and breathed fire with 100 million times the power it has today," Joss Bland-Hawthorn, an astronomer and professor at the University of Sydney, said in a statement.

The first indications of this came in 1996, as astronomers observed the glow in a large cloud of gas below the galactic core called the Magellanic Stream. However, it wasn't until 2010, when NASA's Fermi Gamma Ray Space Telescope spotted immense bubbles of gas expanding out from the centre of the galaxy, that the source for this glow was found. Working from that discovery, Bland-Hawthorn teamed up with Dr. Ralph Sutherland from Mount Stromlo Observatory and Dr. Phil Maloney from the University of Colorado to show that the same eruption that caused the gas bubbles also caused the light show in the Magellanic Stream, and it all happened two million years ago.

A computer simulation designed to show a black hole going through one of these outbursts in real-time, gives a good indication of what we would have seen at the time:

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According to the University of Sydney news release, when asked if this kind of outburst could happen again, Professor Bland-Hawthorn replied, "Yes, absolutely!"

"There are lots of stars and gas clouds that could fall onto the hot disk around the black hole," he said. "There's a gas cloud called G2 that astronomers around the world are anticipating will fall onto the black hole early next year. It's small, but we're looking forward to the fireworks!"

(Image courtesy: NASA/Dana Berry/SkyWorks Digital)

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