Observations of the jet of the supermassive black hole M87: the fact of its rotation has been established

An international team of researchers, including scientists from FIAN and MIPT, analyzed radio interferometric observations for 2022 of the M87 galaxy and found that the jet – a plasma jet escaping from the black hole at its center – periodically changes its direction. According to scientists, this proves that the central supermassive black hole is rotating. The work was published in the journal Nature.

The giant galaxy M87 in the constellation Virgo, located 55 million light-years from Earth, attracts astrophysicists with its relative proximity and the supermassive black hole at its center, which is 6.5 billion times more massive than the Sun. Matter falling into a black hole makes the galactic core an active source of radiation across the entire electromagnetic spectrum. This process is accompanied by the release of a large amount of energy. Some of the surrounding falling matter is ejected from the black hole and generates a jet in which the matter moves at almost the speed of light. The jet extends far beyond the galaxy, 4,900 light years. Due to its high brightness and proximity, the relativistic jet was first discovered in M87 back in 1918. More than a century later, in 2019, the Event Horizon Telescope discovered a central radio source and an asymmetric ring structure consistent with the expectations of general relativity in the presence of a supermassive black hole. However, its rotation, which is crucial in the formation and evolution of jets and the galaxy, has not been directly observed.

Scientists have noted a change in the positional angle of the jet’s direction since the very first observations in the radio range with high angular resolution in 2000. However, the origin of such structural changes was not clear. This may be influenced by the manifestations of black hole activity and the release of matter into the jet or the development of plasma instabilities.

Other observations of the M87 jet in 2009 allowed scientists to reconstruct the jet’s heterogeneous structure, which resembles a tweed pattern in the form of a woven braid of spiral fibers. Simulations demonstrated that the twisting of the central fibers is caused by instabilities developing in the plasma jet. They can develop when the velocity field across the jet is inhomogeneous. For example, these could be two different plasma flows, the interaction of which produces the observed phenomena. Such a spiral structure of the fibers can also be caused by physical processes in the immediate vicinity of the black hole. It is probably the Lense-Thirring precession that leads to the development of these instabilities in the jet itself.

“Such observations allow us to study the phenomena of plasma physics and the life of the Cosmos in general. Currently, global positioning networks are actively developing – a satellite navigation system that provides distance measurements and determines the location of objects in the world coordinate system. They are based on monitoring stars that are constantly moving and are not in one position. The system is not very stable, and the idea is currently being actively promoted to use distant quasars in its operation – the same active nuclei whose jet is actually directed towards us, which makes them the brightest points for the Earth. Unlike stars, their position is stable, but due to the fact that the jet is inhomogeneous, an object in the sky may shift, which affects the accuracy of the system. A detailed study of quasars and jets allows us to perform the necessary correction and restore the absolute position of objects,” Evgenia Kravchenko.

Scientists still have many questions to answer, such as what the structure of the disk is and what the exact spin of the supermassive black hole M87 is. Research can only be carried out using long-term observations with high angular resolution.