Black holes are space objects of such formidable density that even light cannot escape their extreme 'gravitational claws'. But just because they are invisible does not mean that we cannot find ways to observe them.
This time, astronomers have mapped the contours of a supermassive vortex in the galaxy IRAS 13224-3809, found in the constellation Centaurus, about 1 billion light-years from Earth.
To achieve this, the researchers used observations of an accreting black hole made by the European Space Agency (ESA) X-ray observatory XMM-Newton.
Here's how accretion works: As matter in space is attracted to the black hole, it reaches such high speeds that the spiral material heats up, reaching temperatures of millions of degrees (and even higher).
This superheated vortex creates radiation that can be detected by space telescopes when X-rays collide and reflect off gas particles in the vicinity of the vortex.
Scientists say observing these interactions is analogous to an echo, and in much the same way that sound reverberations can inform us about the shape and structure of three-dimensional spaces, so that 'light echoes' can also reveal the invisible shape of supermassive black holes.
A black hole feeding on the surrounding gas, with coronal vibrations. (ESA)
“Similarly, we can observe how X-ray echoes propagate in the vicinity of the black hole to map out the geometry of the region and the state of the accumulation of matter before it disappears into the singularity,” explains astrophysicist William Allston of the University of Cambridge.
“It looks like a cosmic echo location.”
The technique called X-ray reverberation mapping is not new, but it is evolving. The light echoes were received by Ollston and his team from over 23 days of observation of IRAS 13224-3809.
In doing so, they saw something they did not expect to see: the black hole's corona – a region of very hot electrons hovering above the object's accretion disk – burst into flames, its brightness changed 50 times in just a few hours.
“As the crown resizes, the light echo changes, as if the ceiling of a house was moving up and down, changing the sound of your voice,” says Alston.
“By tracking the light echo, we were able to see this changing corona and – even more interesting – get much better values for the mass and rotation of the black hole than we could have determined if the corona had not changed in size.”
This glimpse of the supermassive black hole IRAS 13224-3809 may be unprecedented in terms of detail.
Researchers now hope to use the same method to study the physics of black holes in many other distant galaxies. Hundreds of supermassive black holes are within range of XMM-Newton, and more will come into view when ESA's Athena satellite goes into orbit in 2031.
What these spinning vortices tell us remains to be seen, but it looks like we are on the verge of some incredible discoveries.
The findings are reported to Nature Astronomy.
Sources: Photo: ESA
