supermassive_black_hole
This image from NASA's Chandra X-ray Observatory shows the center of our Galaxy, with a supermassive black hole known as Sagittarius A* (Sgr A* for short) in the center. NASA

A supermassive black hole at the heart of the Milky Way galaxy erupted in a powerful explosion two millions years ago, lighting up a cloud 200,000 light years away, a team of researchers led by the University of Sydney said, adding that such a colossal explosion could happen again.

According to researchers, the latest discovery confirms that black holes can “flicker,” moving from maximum power to switching off over short periods of time.

“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, a professor from the University's School of Physics and the lead author of the study, said in a statement.

The researchers said that the evidence of the new findings comes from a lacy thread of hydrogen gas named the “Magellanic Stream,” which trails behind the Milky Way galaxy’s two small companion galaxies called the Large and Small Magellanic Clouds.

“Since 1996, we've been aware of an odd glow from the Magellanic Stream, but didn't understand the cause,” said Martin Rees, who has been Astronomer Royal since 1995, and was one of the first scientists to suggest that massive black holes power quasars. “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 centre of our galaxy.”

In 2010, NASA’s Fermi satellite discovered two huge bubbles of hot gas billowing out from the centre of the Milky Way galaxy, covering almost a quarter of the sky.

Earlier this year, University of California, Santa Cruz, developed computer simulations of those bubbles and suggested that they were caused by a huge explosion from Sagittarius A* -- the region around the Milky Way galaxy's supermassive black hole -- within the last 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,” said Bland-Hawthorn, who, along with other researchers, calculated that the explosion must have occurred two million years ago because the energy release shown by the Santa Cruz group perfectly matched that from the Magellanic Stream.

According to scientists, the surrounding stars don't produce enough light to explain the glow, so the only explanation for the glow is that it had to be produced from the massive black hole. Bland-Hawthorn said also that a similar explosion could happen in the future as there are many stars and gas clouds that could fall onto the hot disk around the black hole.

"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,” Bland-Hawthorn said.

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