Hot energetic wind coming from an active galactic core in low light

Supermassive black holes in the universe swallow gas around them. The incoming gas is called the black hole accretion stream. In a study published in Nature astronomy, the group led by Professor YUAN Feng of the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences, as well as the group led by Professor LI Zhiyuan of Nanjing University, found direct evidence of the existence of an energetic hot wind launched from the hot accretion flow on a weakly accretive supermassive black hole, representing a step towards understanding the accretion processes around the black hole.

There is a supermassive black hole in almost every galaxy in the universe. The gas around the black hole will be accreted and form an accretion disk. Strong radiation is emitted by the accretion disc, which is the source of the radiation of the first image of black holes people obtained in 2019.

Depending on the temperature of the gas, black hole accretion flows are divided into two types, namely cold and hot flows. Theoretical studies carried out by the SHAO group over the past ten years have predicted that strong winds must exist in the hot accretion flows that typically feed low-light active galactic nuclei (LLAGN). These winds also play a crucial role in the evolution of galaxies, according to cutting-edge cosmological simulation Illustris-TNG. However, evidence of direct observation of such a wind has proven difficult to obtain.

Researchers in this study found strong observational evidence of an energetic flow of M81 *, a prototype of LAGN residing in the nearby massive spiral galaxy Messier 81 by analyzing a high-quality x-ray spectrum. The spectrum, which has unparalleled resolution and sensitivity, was taken by the Chandra X-ray Observatory in the years 2005-2006, but has so far remained unexplored for the wind aspect.

The outgoing flow of M81 * is evidenced by a pair of Fe XXVI Lyα emission lines which shifted towards red and blue almost symmetrically at an overall line-of-sight speed of 2800 kilometers per second, and a high Fe XXVI Lyα-to-Fe XXV K high line ratio which implies a temperature of 140 million degrees Kelvin of the line emitting plasma.

To interpret the high speed, high temperature plasma, the researchers performed magnetohydrodynamic simulations of the hot accretion flux on M81 * and produced a synthetic x-ray spectrum of the wind launched from the hot accretion flux as predicted. by numerical simulations. The predicted emission lines were in agreement with the Chandra spectrum, providing evidence for the existence of a hot wind. The energy of this wind was found to be strong enough to affect the environment near M81 *.

This study revealed the missing link between observations and the theory of hot accretion flows, as well as the latest cosmological simulations with AGN feedback.