American astronomers using the ALMA radio telescope complex have obtained an image of the supermassive black hole Sagittarius A * and proved that its accretion disk is rotating. The results of observations and calculations were published on the pages of Nature.
In the center of the Milky Way, 26 thousand light years from Earth, there is a small radio source Sagittarius A with a diameter of 6.7 10 9 km. Observations of the object for 16 years have shown that its weight is about 4.3 million solar masses. The results indicate that there is a supermassive black hole at the center of our galaxy.
There are several hypotheses for the formation of black holes of this mass, one of which is the accretion of matter onto a black hole of stellar mass. The difficulty lies in concentrating a sufficient amount of matter in a small volume, for which matter must have a very small initial angular momentum – small rotation. The spinning, incandescent X-ray emitting matter falling on the black hole creates an accretion disk, thanks to which in 2019 the participants of the Event Horizon Telescope collaboration published an image of the galaxy M87, located at a distance of 53.5 million light years.
So far, astronomers have recorded a spherical stream of hotter (107 ° C) and less hot (102-104 ° C) gas, but no evidence of its rotation. This time, the researchers set themselves the task of studying cooler clouds of gas. The ALMA radio telescope complex recorded radiation in the hydrogen spectral line (1.3 mm H30α recombination line) – the only radiation emitted by a “cold” substance. Photons of this length are emitted when hydrogen atoms continually lose and recapture their electrons.
The analysis showed that the distribution of photons in a black hole resembles an oblong donut with a hole in the center – where the black hole is. Longer wavelength light (redshift) comes from one side of the object, and shorter wavelength (blue shift) on the other. The redshift side is offset 0.11 arc seconds northeast, and the blue offset side is offset the same distance southwest. These observations may indicate that the disk is actually spinning.
Further calculations showed that the weight of the accretion disk can be 0.00001-0.0001 solar masses (depending on the thickness of the disk), and the rate of fall of the material is 2.7×10 -10 solar masses per year.