At the center of our Galaxy is the Milky Way — a unique area of the sky where the most diverse stellar and gas structures are concentrated. Its central stellar disk was formed billions of years ago and contains mainly an old stellar population, which is difficult to study in the visible range due to the large amount of gas and dust in the line of sight.
Until now, the properties of the stellar disk were known mainly from observations in the infrared range, where the light of stars partially passes through clouds of interstellar dust. But you can look at the same area of the starry sky in another way — X-ray radiation with energies of more than several kiloelectronvolts is able to break through dust and gas and provides a rare opportunity to see the processes taking place in the very center of the Galaxy.
X-ray space telescopes have previously actively studied the region of the central stellar disk, but until now, in these observations, the intrinsic X-ray radiation of the CSD could not be separated from the radiation of other objects that are also located in the center of the Galaxy.
For the first time, it was possible to isolate the intrinsic X-ray radiation of the CSD against the background of other structural components of the Galaxy using the ART-XC telescope named after M.N. Pavlinsky on board the Spektr-RG Observatory, thanks to the unique characteristics of the instrument and wide-angle uniform mapping.
A rather difficult task for researchers was the need to "subtract" "extra" radiation from the ART-XC observation data.
After careful removal of the contribution from bright point sources and background noise, an extended structure appeared on the map, almost coinciding in shape and size with the disk known from infrared observations. Its characteristic thickness is about 90 parsecs, and the length along the plane of the Galaxy is about 300 parsecs.
From the data obtained, it became clear that the X-ray radiation of the central disk is most likely the combined glow of tens or even hundreds of thousands of weak sources that are not visible separately from a distance of eight kiloparsecs — this is how much separates us from the central regions of the Galaxy. It is worth noting that the nature of the "X-ray ridge of the Galaxy" — X-ray radiation extending along the entire Milky Way — was previously explained in the same way.
Thus, it became clear that not only ordinary stars are the source of radiation from the central stellar disk.
The main candidates for the role of such weak sources are cataclysmic variables — binary systems in which the substance of the companion star flows to a white dwarf and heats up to millions of degrees. Their collective radiation can form an X-ray background that closely repeats the distribution of stellar mass.
The X-ray map of the center of the Galaxy, obtained from the analysis of data from the ART-XC telescope, is in good agreement with models of the distribution of stellar mass measured in infrared radiation. For the first time, scientists managed to build a three-dimensional model of the distribution of X-ray radiation and measure the total luminosity of the CSD — about 6x1036 erg/s.
The data obtained help to more accurately determine the contribution of various components to the X-ray radiation of the central region of the Galaxy and distinguish the glow of weak stellar systems from the radiation of hot plasma filling the interstellar space. This is important both for understanding the evolution of compact objects in the core of the Milky Way and for building models of its structure.