They observe how the Andromeda black hole feeds


An international scientific team, led by the University Observatory of Munich and the Institute of Astrophysics of the Canary Islands, obtains a direct visualization of the feeding process of the central black hole of the Andromeda galaxy. The study reveals the existence of long filamentary structures of dust and gas that spiral from the outside of the black hole to its center. The results, which are published in The Astrophysical Journal, have been obtained thanks to images from the Hubble and Spitzer space telescopes.

Andromeda Galaxy 560mm FL

The Andromeda galaxy, visible to the naked eye, is one of the closest to the Milky Way. In its center it houses a supermassive black hole, with more than 100 million the mass of our Sun. However, this black hole, as well as the one in the center of our galaxy, called Sagittarius A*, are the least active known, since They emit little radiation.


The activity of a black hole depends on the way it is fed, that is, on how the incoming matter approaches its center. In the case of the Milky Way, it is difficult to track this activity due to our position close to the plane of the galaxy, where dust obscuration is very high and densely populated with stars; The same does not happen in Andromeda, where it is possible to observe its central black hole with fewer impediments.


Now, using combined observations from the Hubble space telescope and the Spitzer space telescope, a scientific team led by the Computational Astrophysics group of the University Observatory of Munich (USM) and the Institute of Astrophysics of the Canary Islands (IAC) has been able to study how the black hole central part of the Andromeda galaxy is being carefully fed.


“Black holes are eager devourers of food and yet delicate,” explains Christian Alig, USM researcher and first author of the article. When fed slowly and progressively, they leave no signs of their food; However, when feeding is forced and excessive, their reaction is violent and aggressive.”


Filaments of matter and spiral trajectories


Thanks to two powerful space telescopes, the team has discovered that the central black hole of the Andromeda Galaxy is fed by long filaments of dust and gas located far from the galaxy's core. “These filaments progressively spiral into the black hole, similar to how water rushes down a sinkhole,” explains Almudena Prieto, IAC researcher and co-author of the study.


While Hubble is able to see the darkening of filaments produced by dust in visible light, the Spitzer telescope distinguishes the same dust filaments, but in the infrared range. In this way, joint observation with both telescopes has been able to reveal a complete view of the accretion process of the material around the black hole. Due to the proximity of the Andromeda galaxy, Spitzer's observations of its nucleus are the most detailed obtained with this telescope to date, and have a level of precision comparable to that achieved by the Hubble telescope.


This study is part of the PARSEC project which aims to investigate, at multiple wavelengths, the core of the closest galaxies and the accretion processes of black holes. Led by the IAC, the project is made up of nearly 50 members from institutions in a large number of countries.

Octavio Alonso