Illustration of a supermassive black hole. Credit: Nasa/ Dana Berry
New Delhi, Sept. 23: A black hole at the core of the Milky Way galaxy swallowed a massive cloud of gas and dust about two million years ago, triggering an enormous eruption that has left its imprints on a stream of gas that stretches halfway across the sky.
An international team of astronomers said today that its studies of the tail of gas called the Magellanic Stream have confirmed that material falling into the Milky Way’s central black hole had triggered a supermassive eruption, or flare, of electromagnetic radiation.
Black holes are the remnants of stars that have exhausted all their fuel and collapsed into objects with such intense gravitational field that not even light escapes from them. Astronomers believe a supermassive black hole about four million times the mass of the Sun exists at the core of the Milky Way.
The first hint of such an eruption at the core of the Milky Way emerged a decade ago when astronomer Joss Bland-Hawthorn at the University of Sydney, Australia, spotted evidence of a wind of radiation sweeping the galaxy about two million years ago.
Three years ago, Harvard University astronomer Meng Su and his colleagues observed two large bubbles of gamma ray light centred on the black hole — adding evidence for the event.
Now, Bland-Hawthorn and other team members have examined the impact such an eruption would have had on the Magellanic Stream, a tail of gas on the outskirts of the Milky Way galaxy.
The astronomers measured the rate at which the gas in the Magellanic Stream is cooling down after being zapped by the eruption from the region of the black hole about 200,000 light years away.
“Our observations are consistent with an eruption about two million years ago,” Dr Greg Madsen, a research associate and team member at the University of Cambridge, said. The findings have been accepted for publication in The Astrophysical Journal.
Astronomers believe such flares associated with central black holes are common in other galaxies. “Our work supports the first direct evidence that this kind of burst happened in our own galaxy,” Madsen said.
Astronomers have developed a picture of the universe that assumes that black holes at the galactic cores periodically grow in size by consuming massive clouds of gas and dust.
“As the material spins around the black hole on its way in, it heats up tremendously and starts producing beams of radiation, then jets and winds,” said Bland-Hawthorn. The heat may generate a burst of radiation strong enough to spew out material.
“This means black holes may be erratic, explosive and unpredictable like volcanoes.”