Astronomers have registered a quasi-periodic flickering of Sagittarius A* — the supermassive black hole at the center of the milky way. According to researchers, the fluctuations of the radiation observed in the millimeter range, can be associated with the occurrence of hot spots in the accretion disk around the compact source. Article published in The Astrophysical Journal Letters.
In the Central part of the milky Way, at a distance of about 26 thousand light years from the Sun, is a compact radio source Sagittarius A*, which probably is a supermassive black hole with a mass of 4.2 million solar masses. This is the closest object of this type, which makes it highly attractive for research. More than 20 years of observations, scientists were able to learn that a black hole surrounded by accretion disc of hot gas, a substance which gradually spirals into the black hole, and the disc from a cold molecular gas and massive hot stars. In addition, the researchers recorded coming from Sagittarius A* flares in radio, near-infrared and x-ray range, however, the question of whether they are periodic for a long time remained open.
Whey Iwata (Yuhei Iwata), Keio University, together with colleagues observed Sagittarius a* in the millimeter range of electromagnetic waves with complex telescopes of the Atacama Large Millimeter Array. Within 10 days, 70 minutes per day, astronomers have recorded the changes in the flux density of the radiation emanating from the source at the center of our galaxy. To the resulting curves, scientists noticed two phenomena: quasi-periodic fluctuations occurring approximately every half hour, and slower, time variation.
The authors have focused on short time oscillations and found that 30-minute period changes of the radiation flux is comparable with the orbital period of the inner edge of the accretion disk with a radius of 0.2 astronomical units. For comparison, mercury orbits the Sun at an average distance of 0.4 astronomical units. According to the group Italy, fluctuations in the light curve could cause hot spots formed due to magnetic disturbances in the hot gas moving in a circular orbit close to a supermassive black hole.
Astronomers hope that the data obtained will be able to tell us about the behavior of the black hole and the gas around it. On the other hand, researchers fear that such a rapid rotation of the inner part of the accretion disk may prevent the project Telescope event horizon (EHT) to image the immediate vicinity of Sagittarius A*. “The faster the motion, the more difficult it is to photograph an object,” says Tomoharu Oka, Professor of Keio University and one of the authors.
In 2019, the project EHT for the first time could see the shadow of the supermassive black hole at the center of the active galaxy M87. This was a landmark event for the whole of astronomy. Read more about the context of such studies can be read in the material “Looking into the abyss”.