The source of radio emission Sgr A* at the center of the Milky Way, which is supposedly a supermassive black hole, behaves chaotically not only in the short term, but also in the long term. Astronomers came to this conclusion by studying how its activity changes. The results of the study were published in the scientific journal Monthly Notices of the Royal Astronomical Society.
“We don’t yet know what causes these random bursts of Sgr A* activity. Previously, we believed that they were caused by clouds of gas or stars periodically approaching a black hole, but we did not find evidence for this theory. We also could not confirm that these flashes are related to the magnetic properties of the gas that surrounds this radio source,” said Jacob van den Eynden, one of the authors of the study, a researcher at the University of Oxford.
Scientists believe that at the center of supposedly all galaxies in the universe is one or even several supermassive black holes. For example, in the core of the Milky Way there is a source of radio emission Sgr A * (Sagittarius A *), which some astronomers also consider such a black hole. Astronomers learned about its existence in the early 1990s by how the attraction of this object affects the orbits of neighboring celestial bodies.
Subsequently, astronomers discovered that Sgr A * is surrounded by several dozen stars and several large clouds of gas, periodically approaching and passing at a dangerous distance from it. These encounters were thought in the past by scientists to generate bursts of Sgr A* activity and lead to bursts of X-rays and other forms of electromagnetic radiation.
Einden and his colleagues questioned the validity of this hypothesis after they made large-scale long-term observations of changes in the level of Sgr A * activity using the Swift orbiting X-ray telescope. This instrument has periodically observed the center of the Milky Way in the X-ray and gamma-ray ranges since 2006, which scientists have used to study the long-term patterns of Sgr A * activity.
An analysis of the data collected by Swift from 2006 to 2019 showed that Sgr A* behaves completely erratically in both the short and long term. Scientists have not been able to identify a single pattern or recurring trend in how the level of its activity and the frequency of flashes produced in the X-ray range of electromagnetic waves changed.
In particular, the frequency of outbreaks was unusually high between 2006 and 2008, then suddenly decreased in the next four years, and in 2012 it started to rise again. The reasons for such chaotic fluctuations in the strength and frequency of outbreaks, according to Einden and his colleagues, are still a mystery to theorists.
At the same time, astronomers hope that subsequent observations of Sgr A * flares using Swift and other orbiting observatories will help them understand if there is at least a minimal connection between these events and the approaches of clouds of gas and stars with a supermassive black hole. Its absence will force scientists to look for alternative explanations for how bursts of activity of supermassive black holes occur, the astronomers summed up.