Will supercomputers used to study black holes be our key to understanding fusion reactors?

  • Tomáš Lanča
  • 03.08.2022
An international team of physicists together with scientists from the Institute of Physics have published an article in the July issue of the scientific journal Monthly Notices of Royal Astronomical Society which describes the behaviour of matter in the vicinity of black holes in an entirely new way. These new models, which are based on supercomputer simulations and describe the behaviour of matter in such an extreme environment, could be already used in practice when solving problems here on earth. They show in high detail how plasma behaves in extreme conditions and could therefore be used to realise the application of fusion reactors as a permanent source of energy for mankind.
Nový obrázekUnderstanding the so-called accretion disks could be a key information for the realisation of fusion reactors on Earth. Source: NASA. Nový obrázekUnderstanding the so-called accretion disks could be a key information for the realisation of fusion reactors on Earth. Source: NASA.

Matter around black holes

If there is any matter in the close vicinity of a black hole – an extremely dense object in space not even light can escape from – it is immediately ionized which means that it decomposes into ions and electrons. This is how plasma, which later forms into a rotating disc around the black hole is created. These disks can then be described using known laws of plasma physics and hydrodynamics. They are very important for current astrophysics research and several well-known physicists are dealing with their research, among them for example is Kip Thorne (born 1940, Nobel Prize for Physics winner)
X-ray observatory satellite XMM-Newton. Source: ESA X-ray observatory satellite XMM-Newton. Source: ESA

Matter in accretion disks can rotate at extreme speeds approaching even the speed of light. In these conditions, an enormous amount of radiation is released thanks to friction.

“If the black hole in the centre of the accretion disk spins too, the efficiency of the system can reach up to 42 %, which releases almost half of the energy described by Einstein’s E=mc2 equation. In comparison, nuclear fission used in nuclear power plants only releases around 0.7 % of energy stored in matter but is still using only about 3 g of Uranium to create 1 MW of electricity.” Explains Mgr. Debora Lančová from the Institute of Physics in Opava, a co-author of the original paper.

Matter under extreme conditions

Matter from the disc falls into the black hole, or in the opposite case, under rare conditions of gravity and magnetism, is accelerated into outer space. The radiation of accretion discs is the only method of studying the close vicinity of black holes. Thanks to extremely high temperatures, the outer rim of the disk releases X-rays, which are (luckily) blocked out by Earth’s atmosphere and can only be observed by X-ray observatory satellites like XMN-Newton, Nustar or the tiny NICER which is placed on the deck of the International Space Station.

The X-ray signal from accretion discs is monitored and interpreted by scientists on Earth who can then determine the properties of the object emitted them, like it’s mass, the rotation speed and other values. But these are objects aren’t just very far away, they are also tiny, which is why we can only observe them as a source of point light, and we cannot determine where exactly the radiation originates. Therefore astrophysicists use various models of accretion disks based on known laws of plasma physics and astrophysics and compare the observed signal with an artificial signal from simulations.

“The existing models have always had one problem; they couldn’t explain all observed aspects of the radiation. In some areas, the simulations failed, even though according to the observed accretion discs, they should work. In our work, we’ve come with a new model, which explained most observed behaviours.  And with that came a new way of looking at the behaviour of matter around black holes.” Says Lančová

Puffy disks around black holes

There are up to a billion black holes in our Galaxy alone, obviously only a fraction of which can be observed. The best ones for observations are the ones which are a part of a so-called x-ray binary – small black holes living alongside with a lighter star, which serves as a source of fresh matter for the accretion disc which then creates strong x-ray signal.

“Observations made by x-ray satellites have shown us, that properties of the signal do not match with the standard ideas about accretion disks, and therefore the generally accepted model isn’t applicable to all instances. Turns out that around smaller black holes, the accretion disk has a slightly different structure than was accepted. You could say that it’s puffier.” Lančová describes.

According to her, the correct model of accretion disks is absolutely vital to determine the properties of a black hole in its centre, since we may never observe it directly and we can only get it’s parameters from the surrounding matter – the accretion disk.

“This means that the current models were giving us wrong information about black holes and created a sort of a gap in our understanding of the signals coming from x-ray binaries and we ended up dealing with an unexplainable mystery. Our model helped to solve this mystery and allowed us to advance in our research once again.” The astrophysicist adds

Supercomputer as a path to fusion power

“One of the ways to correctly describe the behaviour of matter in extreme conditions like these are supercomputer simulations.” Says Lančová. According to her, these simulations describe plasma as a fluid with a strong magnetic field which “flows” into the black hole and releases a high amount of energy. Vortexes and other turbulent flows are common in this fluid and help keeping the flux stable. However, they also make the simulations extremely difficult. In cooperation with a Polish supercomputer centre, the international team managed to get enough resources to run these simulations and investigate a whole new way to look at accretion disks around a black hole.
Simulations show us the complicated behaviour of the plasma which interacts with the magnetic field, radiates energy and this radiation affects it back. A behaviour of matter this complex can not be described or simulated by conventional models, jut like you can not accurately describe the flow of water in a steep, narrow mountain spring.

“In our study we introduce a model which describes everything much more accurately and brought us new opportunities, for example for the research of plasma in extreme conditions, which is currently a hot topic in laboratories around the globe trying to find the answer to running a fusion reactor, the possibly inexhaustible source of energy of the future.” Lančová finishes.