Astronomers have discovered that powerful radio jets from a supermassive black hole – which normally suppress star formation – are actually stimulating the production of cold gas in the galaxy’s halo, proving the existence of a powerful feedback mechanism that potentially fuels future star birth.
The study, published this week in the Astrophysical Journal and led by Helen Russell of Cambridge University, may shed light on the complex relationship between supermassive black holes and their host galaxies – helping explain the workings of the cosmic “thermostat” that controls the launching of radio jets from the supermassive black hole.
"This supermassive black hole is regulating the growth of the galaxy by blowing bubbles and heating the gases around it. Remarkably, it also is cooling enough gas to feed itself,” said Brian McNamara, a University Research Chair in Astrophysics at the University of Waterloo, and co-author on the paper."
The researchers used the Atacama Large Millimeter/submillimeter Array (ALMA) to study a galaxy at the heart of the Phoenix Cluster, an uncommonly crowded collection of galaxies about 5.7 billion light-years from Earth.
The central galaxy in this system has a supermassive black hole that is in the process of devouring star-forming gas, which fuels a pair of powerful jets that are erupting from the black hole in opposite directions. Astronomers refer to this type of black-hole powered system as an active galactic nucleus (AGN).
Earlier research with NASA’s Chandra X-ray observatory revealed that the jets from this AGN are carving out a pair of giant "radio bubbles," huge cavities in the hot, diffuse plasma that surrounds the galaxy. Astronomers believed that the gas surrounding these expanding bubbles would be too hot to condense into material for future stars.
Yet in 2014, McNamara, Russell, who was then a postdoctoral fellow at Waterloo, and their colleagues found evidence of a powerful feedback mechanism in another AGN that was somehow producing an enormous amount of cold molecular gas to fuel new star formation and the nuclear black hole itself.
The latest ALMA observations indeed reveal long filaments of cold molecular gas condensing around the outer edges of the radio bubbles. These filaments extend up to 82,000 light-years from either side of the AGN. They collectively contain enough material to make 10 billion suns.
"With ALMA we can see that there’s a direct link between these radio bubbles inflated by the supermassive black hole and the future fuel for galaxy growth," says Russell, currently an astronomer with the University of Cambridge, and lead author on the paper. "This gives us new insights into how a black hole can regulate future star birth and how a galaxy can acquire additional material to fuel an active black hole."
This news story was adapted with permission from the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.