The Environment Around a Supermassive Black Hole

Artist's impression of the innermost regions around a supermassive black hole, showing an accretion disk visually distorted by gravity surrounding the event horizon, and powering an outflow of material. Image credit: CfA/M. Weiss.

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During the past week, NuSTAR observed the nearby active galactic nucleus (AGN) I Zwicky 1 in coordination with the JAXA/ESA/NASA’s XRISM and ESA’s XMM-Newton X-ray observatories. I Zwicky 1 is a unique AGN from which we can learn a lot about the fundamental physics at work as material spirals into a black hole, and the processes by which supermassive black holes grow and are able to have a profound impact on their host galaxies by AGN feedback. In this AGN, we observe X-rays reflecting off the innermost regions of the accretion disk, allowing us to probe the extreme environment just outside the event horizon of the black hole. In addition, I Zwicky 1 is seen to launch an ultrafast outflow: a wind from the inner accretion disk reaching velocities up to 30% of the speed of light. These outflows carry significant energy into their host galaxies and understanding how they are launched is an important step towards understanding AGN/host galaxy feedback. I Zwicky 1 is often seen to launch X-ray flares originating in the corona, and the outflows are seen to evolve in response to these flares. Through these observations, important new insights are expected into the structure of the accretion disk around a rapidly growing black hole, the launching mechanism of the ultrafast outflows, and the connection between these outflows and the innermost regions of the accretion disk and the corona.
Author: Dan Wilkins (Research Assistant Professor, The Ohio State University)

Source: NASA's Nuclear Spectroscopic Telescope Array (NuSTAR)/News

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XMM-Newton sees light echo from behind a black hole

Ligh echoes behind a Black Hole

For the first time, astronomers have seen light coming from behind a black hole.

Using ESA’s XMM-Newton and NASA’s NuSTAR space telescopes, an international team of scientists led by Dan Wilkins of Stanford University in the USA observed extremely bright flares of X-ray light coming from around a black hole.

The X-ray flares echoed off of the gas falling into the black hole, and as the flares were subsiding, the telescopes picked up fainter flashes, which were the echoes of the flares bouncing off the gas behind the black hole.

This supermassive black hole is 10 million times as massive as our Sun and located in the centre of a nearby spiral galaxy called I Zwicky 1, 800 million light-years away from Earth.

The astronomers did not expect to see anything from behind the black hole, since no light can escape from it. But because of the black hole’s extreme gravity warping the space around it, light echoes from behind the black hole were bent around the black hole, making them visible from XMM and NuSTAR’s point of view.

The discovery began with the search to find out more about the mysterious ‘corona’ of the black hole, which is the source of the bright X-ray light. Astronomers think that the corona is a result of gas that falls continuously into the black hole, where it forms a spinning disk around it – like water flushing down a drain.

This gas disk is heated up to millions of degrees and generates magnetic fields that get twisted into knots by the spinning black hole. When the magnetic field gets tied up, it eventually snaps, releasing the energy stored within it. This heats everything around it and produces the corona of high energy electrons that produce the X-ray light.

The X-ray flare observed from I Zwicky 1 was so bright that some of the X-rays shone down onto the disk of gas falling into the black hole. The X-rays that reflected on the gas behind the black hole were bent around the black hole, and these smaller flashes arrived at the telescopes with a delay. These observations match Einstein’s predictions of how gravity bends light around black holes, as described in his theory of General Relativity.

The echoes of X-rays from the disk have specific ‘colours’ of light and as the X-rays travel around the black hole, their colours change slightly. Because the X-ray echoes have different colours and are seen at different times, depending where on the disk they reflected from, they contain a lot of information about what is happening around a black hole. The astronomers want to use this technique to create a 3D map of the black hole surroundings.

Another mystery to be solved in future studies is how the corona produces such bright X-ray flares. The mission to characterise and understand black hole coronas will continue with XMM-Newton and ESA’s future X-ray observatory, Athena (Advanced Telescope for High-ENergy Astrophysics).

The team published their findings in Nature. DOI: 10.1038/s41586-021-03667-0

Source: ESA/Space Science

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