Around 3.5 million years ago, a gigantic energy flare punched out from the centre of our galaxy, the Milky Way. The radiation it released erupted in two energized cones that were so powerful, the impact was felt 200,000 light-years away.
The flare, called a Seyfert flare, started out small near the center of the galaxy that's dominated by a supermassive black hole. As the cones formed and flashed their way through the galaxy, they expanded.
The flare was felt in the Magellanic Stream 200,000 light-years away, a trail of gas from nearby dwarf galaxies like the Large and Small Magellanic Clouds.
What could trigger such a huge explosion? Researchers believe it was nuclear activity connected to the black hole. The black hole is called Sagittarius A, or Sgr A*. Compared to our sun, the black hole is 4.2 million times more massive.
Researchers were able to use data from the Hubble Space Telescope to understand and calculate the explosion. Their findings will publish in The Astrophysical Journal.
"The flare must have been a bit like a lighthouse beam," said Joss Bland-Hawthorn, study author and professor at the University of Sydney and Australia's ARC Centre for All Sky Astrophysics in 3 Dimensions, called ASTRO 3D. "Imagine darkness, and then someone switches on a lighthouse beacon for a brief period of time."
The researchers determined the explosion happened 3.5 million years ago, about the time ancient human ancestors like Australopithecines were in Africa. The asteroid collision that led to the extinction of the dinosaurs happened 63 million years before.
The explosion lasted for about 300,000 years.
"This is a dramatic event that happened a few million years ago in the Milky Way's history," said Lisa Kewley, study co-author and director of ASTRO 3D. "A massive blast of energy and radiation came right out of the galactic center and into the surrounding material. This shows that the center of the Milky Way is a much more dynamic place than we had previously thought. It is lucky we're not residing there."
This research follows up on previous work by Bland-Hawthorn establishing that the explosive event was related to activity from the black hole, rather than a nuclear starburst. But the researchers acknowledged that future research will be needed to help determine more about the evolution of black holes and how that behavior can influence galaxies.
"These results dramatically change our understanding of the Milky Way," said Magda Guglielmo, study co-author from the University of Sydney. "We always thought about our Galaxy as an inactive galaxy, with a not so bright center. These new results instead open the possibility of a complete reinterpretation of its evolution and nature. The flare event that occurred three million years ago was so powerful that it had consequences on the surrounding of our Galaxy. We are the witness to the awakening of the sleeping beauty."
