Black holes belch out intergalactic smoke

Astronomers have just watched the evolution of streamers of gas around an active black hole – and they look a bit like the smoke produced by a volcanic eruption.

The team used the ultra-sensitive Low-Frequency Array (LOFAR) in the Netherlands, as well as the Spektr-RG space observatory, to study a system of 20 galaxies called Nest200047, 200 million light-years away. One of these galaxies has an active black hole at its heart, which produces radio jets that in turn create bubbles and other structures in the surrounding gas.

The researchers found that the galaxy group was home to all different ages of these structures, showing their evolution over hundreds of millions of years.

“Our investigation shows how these gas bubbles accelerated by the black hole are expanding and transforming in time,” says astronomer Marisa Brienza, from the University of Bologna and lead author of the study, published in Nature Astronomy.

“Indeed, they create spectacular mushroom-shaped structures, rings and filaments that are similar to those originating from a powerful volcanic eruption on planet Earth.”

Black holes have a reputation as cosmic monsters, devouring everything they come across. But in that process, they also release enormous amounts of energy, including massive jets of particles moving close to the speed of light. These streams create bubbles of particles and magnetic fields that then influence the intergalactic medium around the black hole.

“LOFAR gave us a unique view of the activity of black holes and their effects on their surrounding environment,” says co-author Annalisa Bonafede, also from the University of Bologna and a member of the Italian National Astrophysics Institute (INAF).

“Our observations of Nest200047 crucially show how magnetic fields and the very old particles accelerated by black holes and consequently aged play a central role in transferring energy to the outer regions of groups of galaxies.”

Credit: University of Bologna

But the study also found that many of these ancient bubbles still haven’t mixed with the surrounding gas even after all this time, likely due to the influence of magnetic fields.

The researchers say this shows that active black holes can have effects on the scale of hundreds of millions of years, as well as on massive spatial scales up to 100 times bigger than the host galaxy.

The team also discovered thin gas filaments around the black hole stretching for as long as a million light-years. The researchers say these are the remnants of gas bubbles produced by the black hole hundreds of millions of years ago. “In the future, we will be able to study the effects of black holes on galaxies and the intergalactic medium with increasing detail,” says Gianfranco Brunetti, co-author and an astrophysicist at the INAF Bologna. “Eventually, we will be able to unveil the nature of the filaments we discovered.”

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