Scientists unravel the mystery of the supermassive black hole at centre of our galaxy: ‘Sleeping dragon’ erupted two million years ago – and will again

The mystery as to why our galaxy’s supermassive black hole is dormant has stumped scientists for decades.
But new evidence suggests that the ‘sleeping dragon’ was in fact active at some point- we just weren’t around to see it.
Astronomers claim that the supermassive black hole erupted two million years ago in an explosion so immensely powerful that it lit up a cloud 200,000 light years away.

Astronomers claim that the supermassive black hole at the centre of our galaxy erupted two million years ago in an explosion so immensely powerful that it lit up a cloud 200,000 light years away

While scientists had previously predicted that such an outburst had occurred, this is the first time they have been able to say when it happened.
The finding is a confirmation that black holes can 'flicker', moving from maximum power to switching off over, in cosmic terms, short periods of time.
‘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,’ said Professor Joss Bland-Hawthorn, lead author of the study published in the Astrophysical Journal.
‘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”,’ said Martin Rees, Astronomer Royal, who was one of the first scientists to suggest that massive black holes power quasars.

 

THIS is what a black hole looks like. Simulation shows disc...

The evidence for the findings comes from a lacy filament of hydrogen gas called the Magellanic Stream.
It trails behind our galaxy's two small companion galaxies, 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.
‘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.’
The region around the galaxy's supermassive black hole and the black hole is called Sagittarius A* (pronounced Sagittarius A-star).
It emits radio, infrared, ultraviolet, X-ray and gamma ray emissions. Flickers of radiation rise up when small clouds of gas fall onto the hot disk of matter that swirls around the black hole.
But scientists had been puzzled by evidence contrary to this activity that revealed there was a cataclysmic event in the past.
‘In particular, in 2010 NASA's Fermi satellite discovered two huge bubbles of hot gas billowing out from the centre of the galaxy, covering almost a quarter of the sky,’ said Professor Bland-Hawthorn.

The large image contains X-rays from Nasa's Chandra Observatory in blue and infrared emission from the Hubble Space Telescope in red and yellow. The inset shows a close-up view of our galaxy's supermassive black hole in X-rays only, covering a region half a light year wide

Earlier this year, computer simulations of the Fermi bubbles made by the University of California Santa Cruz controversially suggested that they were caused by a colossal explosion from Sagittarius A* within the last few million years.
‘When I saw this research I realised 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.’
The realisation that these black holes can switch on and off within a million years, which given the universe is 14 billion years old means very rapidly, has been described by researchers as a ‘significant discovery’.
Professor Bland-Hawthorn said it is certain that this event will happen again.
‘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.’