Milky Way’s black hole set to eat giant gas cloud

Astronomers will watch the feast in real time

Astronomers will watch the feast in real time
Astronomers will watch the feast in real time

This simulated view shows a gas cloud (just above centre, with its orbit shown in red) that has been observed approaching the supermassive black hole at the centre of the Milky Way. This is the first time ever that the approach of such a doomed cloud to a supermassive black hole has been observed and it is expected to break up completely during 2013. The stars orbiting the black hole are also shown along with blue lines marking their orbits. The stars and the cloud are shown in their actual positions in 2011.

In this artist’s impression, the gas cloud’s orbit is shown in red, while the blue lines mark the paths of stars around the black hole

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Credit: ESO

 
In a paper to be published in the journal Nature on 5 January, astronomers at the Max Planck Institute for Extraterrestrial Physics in Germany have detailed how they will be able to watch a large gas cloud being sucked into the supermassive black hole that lies at the heart of our Galaxy.
 

Most of the time, Sagittarius A*, the black hole at the Milky Way’s centre, lies dormant; only occasionally does the black hole emit flares, which originate from matter falling towards the event horizon, heating up and releasing energy. But in 2013 a large gas cloud will come within 40 billion km, or 36 lighthours of the black hole, and is expected to be sucked into it.

The gas cloud was first detected in infrared images in 2002, measures about 250 times the Earth-Sun distance across and has a mass roughly three times that of Earth. Composed mostly of hydrogen and helium, it is travelling at a speed of over 8 million km/h towards the black hole, its speed having doubled over the past seven years.

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A simulation of the gas cloud being torn apart by the black hole

 
Credit: ESO/MPE/M.Schartman

 

When it nears the accretion zone of the black hole, which has a mass 4.3 million times that of the Sun, scientists expect to see the cloud ripped apart by the tidal forces that surround it. When this happens, the temperature of the cloud will increase rapidly, from 550°K (280°C) to several million degrees Kelvin. This will result in much higher levels of x-ray emission from the black hole region.

“Detailed observations of the radiation from the Galactic centre over the next years will give us the unique opportunity to probe the properties of the accretion flow and observe the feeding process of a supermassive black hole in real time,” predicts the Max Planck Institute’s Stefan Gillessen, who is lead author of the paper.