The ALMA telescope has captured the first ever images of a black hole's accretion disk - a "donut" of heated gas and matter that revolves around it and which it gradually absorbs, according to an article published in the Astrophysical Journal Letters.
“In explaining the various features of quasars, we have long believed that active supermassive black holes are surrounded by a donut-like structure of gas and dust. We could not see her, since she is very small. It was only thanks to ALMA's ultra-high resolution that we were able to realize this dream and confirm that such a structure exists,”says Mastoshi Imanishi of the Japanese National Astronomical Observatory in Tokyo.
Space donuts and bagels
Supermassive black holes can be found at the center of almost every galaxy. Unlike black holes, which appear when stars collapse, their mass is several million times that of the Sun. They periodically absorb stars, other celestial bodies and gas and eject part of the captured matter in the form of jets - beams of heated plasma moving at near-light speed.
These emissions, according to astronomers, are the result of the fact that black holes are unable to absorb matter in unlimited quantities. There is a certain boundary, which astrophysicists call the Eddington limit: when it is reached, the substance begins to accumulate in the vicinity of the black hole in the form of a hot "donut" - an accretion disk, where particles rub against each other, heat up to ultra-high temperatures and are ejected into space.
Not all black holes behave this way, explains Imanishi. For example, the object Sgr A * in the center of our galaxy is distinguished by a modest disposition and appetite, it has no jets and an accretion disk. The question of how the accretion disk is formed and why some black holes sharply lose their appetite or, conversely, acquire it, has become one of the main questions in astronomy.
Japanese astrophysicists took the first step towards solving this mystery by observing the spiral galaxy M77 in the constellation Cetus (one of the closest neighbors of the Milky Way) with the ALMA microwave telescope on the high plateau Chahnantor in Chile.
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Black hole lunch
The disk of this galaxy is turned in our direction "facing", which allows astronomers to follow what is happening in its center, where one of the most active and brightest supermassive black holes in the immediate vicinity of the Milky Way is located.
To search for a "donut" in its center, scientists from Japan went for a trick: they observed two types of molecules that may be present in the vicinity of a black hole, but behave differently in different conditions. For example, carbon monoxide molecules, which ALMA can distinguish well, are found in almost all corners of galaxies and can emit microwaves in almost any conditions.
On the other hand, substances such as hydrocyanic acid or some aldehydes (the simplest compounds of oxygen, hydrogen and carbon) only become visible to ALMA antennas when they are in particularly dense clouds of gas. The accretion disk, astronomers explain, should be much denser than the surrounding clusters of matter, and can be detected by observing the excess of these two compounds.
The idea paid off - Japanese astrophysicists managed to obtain the first detailed photographs of the "donut" of the accretion disk and unexpectedly revealed some of its properties. For example, it turned out that it has an elongated and uneven shape - this suggests that its rotation is controlled by random processes, and not only the attraction of the "owner" of the center of the galaxy.
Astronomers hope that further observations of M77 will help to understand exactly how its "donut" took on such an unusual shape and why the black hole in the center of the Milky Way does not have one.
