Most black holes are too small on the sky for us to determine their immediate environment, but we can still explore these mysterious objects by watching how matter behaves as it nears, and falls into them.
Astronomers use ‘cosmic echo-location’ to map black hole surroundings
As material spirals towards a black hole, it is heated up and emits X-rays that, in turn, echo and reverberate as they interact with nearby gas. These regions of space are highly distorted and warped due to the extreme nature and crushingly strong gravity of the black hole.
Now, researchers have used the European Space Agency’s XMM-Newton X-ray observatory to track these light echoes and map the surroundings of the black hole at the core of an active galaxy. Their results are reported in the journal Nature Astronomy.
Named IRAS 13224–3809, the black hole’s host galaxy is one of the most variable X-ray sources in the sky, undergoing very large and rapid fluctuations in brightness of a factor of 50 in mere hours.
“Everyone is familiar with how the echo of their voice sounds different when speaking in a classroom compared to a cathedral – this is simply due to the geometry and materials of the rooms, which causes sound to behave and bounce around differently,” said Dr William Alston from Cambridge’s Institute of Astronomy, lead author of the new study.
“In a similar manner, we can watch how echoes of X-ray radiation propagate in the vicinity of a black hole in order to map out the geometry of a region and the state of a clump of matter before it disappears into the singularity. It’s a bit like cosmic echo-location.”
Image: Artist's impression of black hole surroundings
Credit: European Space Agency
Reproduced courtesy of the University of Cambridge
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