Researchers believe a supermassive black hole at the center of our galaxy exploded with such force two million years ago that it lit up a cloud 200,000 light-years away.
"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," lead author Professor Joss Bland-Hawthorn University of Sydney said in a statement.
The finding adds evidence to the idea that black holes can "flicker" by switching on and off.
Evidence of the giant black hole explosion comes from the ethereal glow in hydrogen gas called the Magellanic Stream.
"It's been long suspected that our Galactic Centre might have sporadically flared up in the past. These observations are a highly suggestive 'smoking gun'," Martin Rees, Astronomer Royal, said.
"Since 1996, we've been aware of an odd glow from the Magellanic Stream, but didn't understand the cause. Then this year, it finally dawned on me that it must be the mark, the fossil record, of a huge outburst of energy from the supermassive black hole at the center of our galaxy."
The central black hole and the area surrounding it are called Sagittarius A*. The area produces ultraviolet, gamma, radio, infrared, and X-rays
"In particular, in 2010 NASA's Fermi satellite discovered two huge bubbles of hot gas billowing out from the [center] of the galaxy, covering almost a quarter of the sky," Professor Bland-Hawthorn, said.
A controversial computer model created by researchers at the University of California Santa Cruz suggested the bubbles were caused by an extreme even within only the past few million years.
"When I saw this research I [realized] that this same event would also explain the mysterious glow that we see on the Magellanic Stream," Professor Bland-Hawthorn said. "Together with Dr. Ralph Sutherland from Mount Stromlo Observatory and Dr. Phil Maloney, from the University of Colorado, I calculated that to explain the glow it must have happened two million years ago because the energy release shown by the Santa Cruz group perfectly matched, to our delight, that from the Magellanic Stream."
Bland-Hawthorn said the surrounding stars don't produce enough light to explain the glow.
"In fact the radiation from stars is one hundred times too little to account for the radiation now or at any time. The galaxy could never have produced enough UV radiation to account for it. So the only explanation was it had to be produced from our dragon, the massive black hole," he said.
A similar explosion could happen again in the future.
"There are lots of stars and gas clouds that could fall onto the hot disk around the black hole," Professor Bland-Hawthorn, 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!"
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