So far unexplained radiation

Scientists from the Institute of Physics in Opava have been evaluating the oscillations of X-rays around black holes over the past few years, which among other things has helped to determine the mass of one of the supermassive holes located in the centres of galaxies. A detailed analysis of this radiation shows that for the most massive objects observed, the observed frequencies of oscillations of this radiation differ significantly from what scientists predict based on models that correspond very well to the same type of oscillations of radiation in observed "small" black holes formed by the collapse of massive stars.

Professor Stuchlik's research group has recently been intensively studying the effect of the hidden matter around supermassive black holes on the so-called oscillations of accretion structures in their vicinity, which affect the nature of the X-rays coming from these structures. "When we observe radiation from hot matter called accretion disks orbiting black holes, we observe two amplified frequencies of radiation. This is emitted from near the so-called event horizon. Interestingly, the two frequencies have an integer ratio, most often 3:2," says Dr Vrba from the Institute of Physics in Opava, co-author of one of the scientific papers. One of the consequences of this research was also the consideration of the existence of wormholes and parallel universes. This new scientific path opens the door to better mapping the distribution of the mysterious dark matter.

The unknown dark matter

Although astronomers have been studying the Universe for centuries, more than 95% of the composition of the Universe is still unknown. It is thought that 68% is hidden energy and the remaining 27% of the unknown composition is hidden matter (usually referred to as "dark matter"). It is known that this component does exist in the Universe, due to a number of otherwise unexplained phenomena, for example from inconsistent observations of galaxy rotation rates. This was pointed out as early as 1932 by the Dutch astronomer Jan Oort (1900-1992) and in 1933 by the Swiss-American astronomer with Czech roots, Fritz Zwicky (1898-1974). Unlike hidden energy, hidden matter is not uniformly distributed in space.

Thanks to its gravity, dark matter forms clusters like visible matter, which is also attracted to these structures. Some more recent research suggests that the presence of dark matter could affect the so-called polarisation of microwave radiation present in the Universe. This phenomenon is thought to be caused by hypothetical particles called axions. But otherwise, no one has any idea what the nature or form of these particles is. There are only speculations, which are difficult to confirm or deny without better observational technology. While the CREDO project (which anyone with a smartphone can join) is trying to decipher the answers about the composition of hidden matter, new research by physicists in Opava is providing information about the more detailed distribution of this matter.

Large amount of dark matter

"We focused on supermassive black holes. It was the discrepancy between astronomical observations and the theoretical values expected around these black holes that led us to think that dark matter might play a big role. This is quite logical, since we only observe hidden matter due to its gravitational effects, and observations suggest that it is found in large quantities in most galaxies in the Universe. So where else should we expect to find more of it than around supermassive black holes in the centre of galaxies, where most of the mass is concentrated," Vrba says.

As it turns out, dark matter is distributed around black holes in considerable quantities. "If we consider the distribution of matter over distances of some 50 radii of a given black hole, taking the event horizon of the black hole as the edge of the black hole, our calculations show that dark matter of 20-200 percent of the black hole's mass is distributed in such a neighbourhood! Just to give an example, if there were a black hole in the centre of our Solar System, its diameter would extend to a quarter of the distance to Mercury, and the hidden matter distributed in the zone up to the orbit of Jupiter would have a mass of up to 8 million Suns!" Vrba explains.

Black holes with rings

This work has also led to the prediction that supermassive black holes may have rings like large planets. "It is because of the dark matter causing gravitational disturbances to the normal spacetime of a black hole that under certain circumstances two disks may form, with matter falling from the outer disk onto the inner disk but not from the inner disk onto the black hole. Of course, this stability is only temporary until the amount of accumulated mass violates the stability conditions of the system. This could be compared to the gaps in the rings around large planets caused by the gravitational effects of moons in the vicinity," Vrba said, adding that this significantly changes the way black holes have been presented in various videos and images. The properties of these rings should then provide further clues to refine the distribution of dark matter not only around black holes themselves, but also on larger scales in the centres of galaxies. In the same breath, however, he adds that we are not yet able to observe such "rings" with current technology.

Original scientific article.

Contact details for further information:

RNDr. Jaroslav Vrba, Ph.D.
Researcher at the Institute of physics in Opava
Email: jaroslav.vrba@physics.slu.cz
Telefon: +420 605 484 525