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Black holes provide extragalactic gases that are important fodder for active galactic nuclei

Regeneration from the outside: Black holes at the center of galaxies don’t just feed on the material of their galactic home — much of the “feeding” can come from outside, astronomers have discovered. Streams of gas from other galaxies, sucked in by previous collisions and close passes, often supply AGNs. This provides valuable clues about the mechanisms by which supermassive black holes grow.

In the heart of all galaxies too Our galaxy is the Milky Way – Sitting supermassive black holes. The enormous gravity of these giants shapes the motions of galactic gases and stars, while at the same time their activity influences the formation of stars and thus the growth of galaxies. When black holes are active, they devour matter, releasing huge amounts of energy in the form of radiation and jets of particles visible across billions of light-years.

Active black holes play an important role in the formation of stars in their galaxies. But where do they get their food from? © ESO / M. Grain Knife, Inc. CC by 4.0

But where do these black holes get the food needed for their growth? True, astronomers have often noted how giants are Gas And Single stars devour. But that alone cannot explain the rapid growth of these galactic nuclei—particularly in the early universe.

Telltale Aberrations

An observation by astronomers led by Sandra Raimondo of the University of California, Los Angeles, now offers a possible answer. They used the Anglo-Australian Telescope in Australia to study the gas and stellar motion in 3,068 galaxies. They looked for cases where the interstellar disk and galactic gases do not rotate in the same direction, but rather deviate from each other or even in opposite directions.

“Larger deviations greater than 30 degrees are considered a clear indication of a pre-galactic interaction, for example a galaxy merger, the engulfment of a dwarf galaxy, or the accretion of extragalactic gases,” Raimundo and her colleagues explain. The latter can occur when the galaxy absorbs gas from nearby neighbors or captures it from a former galactic corridor. Our Milky Way is also large extragalactic parts.

Strange gases in young galaxies

The interesting thing is: astronomers have long suspected that such exotic, non-periodic gases play an important role in replenishing material for central black holes. “The presence of the anomalously rotating structures enhances the flow of gas into the center of the galaxy,” the researchers explained. This gives the central black hole more “feeding” than would normally be found in the core region of developing galaxies.

Indeed, observational data showed that discrepancies between gas and stellar motion are particularly common in young galaxies: In 25 percent of these elliptical or irregular galaxies, the orientation of the gas and stellar disk was tilted by more than 45 degrees. In many cases, the gases formed streams that extend tens of thousands of light-years outward, sometimes reaching into neighboring galaxies.

Extragalactic food increases activity

And not only that: in galaxies with extragalactic gaseous components, the central black holes were also significantly more active. Astronomers found that 20 percent of all deviant galaxies had AGNs, and 43 percent showed a liner imprint. like Liner galaxies It has a particularly large amount of ionized gas in its center and is therefore considered a transition between inactive and active galactic nuclei.

“Our study therefore proves that the presence of antistellar gas is associated with a higher proportion of active supermassive black holes,” says Raimundo. Because of the galaxies without such embedded foreign gases, only seven percent had active galactic nuclei and 15 percent were LINER galaxies. “It is clear that conditions in deviant galaxies are particularly favorable for active galactic nuclei and LINER,” the team said.

More supplies for the black hole

Astronomers suspect that the alien gas is well suited to “feed” for two reasons: First, it replenishes the inner gas supply of the main galaxy, which simply means more supplies are available to the black hole. On the other hand, these oblique motion components reduce the angular momentum of the galactic matter. Thus the gas slows down and falls faster towards the center of the galaxy.

According to the researchers, their results confirm that mergers and extragalactic gas flows play an important role in “feeding” supermassive black holes. “This is the first time that a direct link has been shown between the presence of foreign gas and the replenishment of food for active black holes,” says co-author Marianne Vestergaard of the Niels Bohr Institute in Copenhagen. (Natural Astronomy, 2023; doi: 10.1038/s41550-022-01880-z)

Source: Nature, University of Southampton