A new study shows that the supermassive black hole lurking at the centre of our Milky Way galaxy is not as dormant as previously thought.

According to the study published 21 June in the journal Nature, the sleeping giant woke up about 200 years ago and swallowed some nearby cosmic objects before going back to sleep. NASA's IXPE space observatory detected an X-ray echo of this powerful resurgence of activity, the researchers said.
The supermassive black hole Sagittarius A*, abbreviated Sgr A*, is four million times more massive than the Sun. It is located at the centre of the Milky Way spiral, 27,000 light-years from Earth.

Last year astronomers revealed the first image of the black hole, or rather the glowing ring of gas surrounding its darkness. Frederic Marin, a researcher at the Strasbourg Astronomical Observatory in Strasbourg, France, and first author of the study, said that Sgr A* "has always been seen as a sleeping black hole."

Most supermassive black holes, which crouch in the centre of their galaxies, go to sleep after swallowing all matter in their vicinity. "Think of a bear hibernating after eating everything around it," Marin told AFP. But the international research team discovered in the late 19th century that Sgr A* woke up from its slumber and consumed all the gas and dust that was unlucky enough to be within its reach.

When it was active, the black hole was "at least a million times brighter than it is today", Marin said. Its awakening was noticeable because nearby galactic molecular clouds began to emit much more X-ray light.
The increase in X-ray light was like "a single firefly hidden in a forest suddenly becoming as bright as the Sun," the French research agency CNRS said in a statement. Astronomers using NASA's IXPE (Imaging X-ray Polarimetry Explorer) space observatory were able to track the X-ray light and found that it pointed directly at Sgr A*.

"The black hole emitted an echo of its past activities, which we were able to observe for the first time," Marin said.
The gravitational pull of black holes is so intense that nothing, including light, can escape. But when matter is pulled beyond the black hole's final boundary, known as the event horizon, it emits enormous amounts of heat and light before disappearing into the darkness.

It is not known exactly what caused Sgr A* to briefly come out of dormancy. Could a star or a cloud of gas and dust have got too close?

 

Astronomers hope that further observations from the IXPE observatory will help them better understand what happened and perhaps reveal more about the origin of supermassive black holes, which remains a mystery.

 

Source: https://www.sciencealert.com/