Simulating the Accretion Disk Around a Black Hole

Black holes are by their very nature, challenging to observe and difficult to spot. It’s usually observations of the accretion disk that reveal properties of the hidden black hole. There is often enough material within the accretion disk to make them shine so brightly that they can often be among the brightest objects in space. A wonderful image has been released which shows the highest resolution simulation of a black hole accretion disk ever created. 

The concept of black holes was first theorised by physicist John Mitchell in 1784 but it was Einstein’s theory of General Relativity that provided the necessary physics to understand them. The first indirect observation of a black hole came in 1971 of Cygnus X-1, the black hole at the centre of our Milky Way galaxy. Since then, more candidates have been identified with the first image of a black hole being captured in 2019.

The anatomy of black holes is fascinating and one of the most useful to astronomers is the accretion disk. It’s a swirling disk of dust and gas that orbits the black hole slowly spiralling inward before being lost beyond the event horizon. As the material accelerates, it heats up due to gravitational forces and emits the energy which we can often detect from Earth in the form of X-rays and ultraviolet radiation. 

A team of researchers from the Tohoku University and the University of Utsunomiya have announced their breakthrough in understanding the accretion disks. Using the power of  supercomputers like RIKEN’s (Japan’s largest comprehensive research institution) “Fugaku” and the National Astronomical Observatory of Japan’s “ATERUI II”, the team created the highest resolution simulations of an accretion disk to model the complex, almost chaotic nature of turbulence in the disks. 

Attempts have been made before but none of them have observed the inertial range largely due to the lack of computer power..until now. This recent study by the Japanese team has successfully reproduced the observed connections between large and small eddies in the accretion disk turbulence, the so called ‘inertial range.’ The results provide a significant step forward in understanding the physics of the environments and processes around black holes and how turbulence allows material to be transported toward the central black hole.

The team also discovered just why ions are selectively heated in accretion disks. Slow magnetosonic waves propagate and dominate the region causing the heating. These waves are low frequency compression waves that are driven by the interaction between a magnetic field and an electrically conductive material. The team showed that it was these waves that are thought to drive the heating process.

The study, which was published in Science Advances on 28 August, will help with the interpretation of data from telescopes like the Event Horizon telescope which is one of a number engaged in black hole studies. 

Source : Supercomputer Simulations Reveal the Nature of Turbulence in Black Hole Accretion Disks