The center of the Milky Way exploded 3.5 million years ago

The supermassive black hole right in the middle of our galaxy may be to blame.

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Jackson Ryan was CNET's science editor, and a multiple award-winning one at that. Earlier, he'd been a scientist, but he realized he wasn't very happy sitting at a lab bench all day. Science writing, he realized, was the best job in the world -- it let him tell stories about space, the planet, climate change and the people working at the frontiers of human knowledge. He also owns a lot of ugly Christmas sweaters.
Jackson Ryan
2 min read

The Milky Way's eruption was so large it affected the Magellanic Stream.

James Josephides/ASTRO 3D

If we could somehow go back in time 3.5 million years and view our galaxy from another location in the universe, we would have seen a cataclysmic flare rip through the Milky Way's center and spill out into the surrounding space.

According to new research, published to preprint database arXiv on Monday, a titanic eruption rippled out from the supermassive black hole at the center of the Milky Way. The flare, officially known as a "Seyfert flare," was so powerful that its impact was felt around 200,000 light-years away as it smashed into the Magellanic Stream, a long trail of gas that orbits the Milky Way.

"The flare must have been a bit like a lighthouse beam," said Joss Bland-Hawthorn, an astronomer at the University of Sydney and first author on the paper. "Imagine darkness, and then someone switches on a lighthouse beacon for a brief period of time." 

You can view an animation of what the cataclysmic event may have looked like below.

Bland-Hawthorn has been chasing this flare and its origins for almost two decades. In 2003, he discovered a huge galactic wind emanating from the center of the Milky Way. Later research confirmed these "bubbles" of radiation coming off our home galaxy and pointed to the mammoth black hole at the center of the Milky Way -- Sagittarius A* (Sgr A*) -- as the culprit.

In 2013, Bland-Hawthorn and colleagues published the first evidence of this eruption in The Astrophysical Journal. To try to  work out exactly when the flare occurred and what caused it, Bland-Hawthorn scoured data from NASA's Hubble Telescope. When he and his team studied the Magellanic Stream, they found evidence it had been whacked by a cataclysmic event from the center of the Milky Way. 

"A massive blast of energy and radiation came right out of the galactic center and into the surrounding material," said Lisa Kewley, an astronomer at Australian National University and director of astrophysics collaborative Astro 3D. "This shows that the center of the Milky Way is a much more dynamic place than we had previously thought."

The researchers suggest the event lasted approximately 300,000 years and began as some of humanity's earliest ancestors walked the Earth. 

But why didn't Earth, which is only about 25,000 light-years from the center of the Milky Way, get smashed by the powerful flare? 

We're lucky, mostly. The huge flare seems to have exploded "up and down" from the galactic plane, rather than across the galaxy. That doesn't make us completely safe from the monster black hole that resides at the galaxy's core. But right now, Sgr A* seems to be pretty settled. 

The research will be published in The Astrophysical Journal later this year.

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