An intergalactic gas cloud is sometimes a dish best served cold. In a new study published June 9 in the journal Nature, a Yale-led team of astronomers found a supermassive black hole about to devour clouds of cold, clumpy gas hurtling toward it. Prior to this, scientists believed that supermassive black holes in the largest galaxies fed on a slow, steady diet of hot, ionized gas from the galaxy’s halo.
“Although it has been a major theoretical prediction in recent years, this is one of the first unambiguous pieces of observational evidence for a chaotic, cold ‘rain’ feeding a supermassive black hole,” said Yale astronomer Grant Tremblay, lead author of the study. “It’s exciting to think we might actually be observing this galaxy-spanning ‘rainstorm’ feeding a black hole whose mass is about 300 million times that of our Sun.”
The discovery offers new insight into the way black holes ingest fuel, a process called accretion. The most common way for black holes to feed is by taking in hot, ionized gas that spirals in slowly from a surrounding disc of cosmic material.
“The simple model of black hole accretion consists of a black hole surrounded by a sphere of hot gas, and that gas accretes smoothly onto the black hole, and everything’s simple, mathematically,” said Michael McDonald, assistant professor of physics in MIT’s Kavli Institute for Astrophysics and Space Research. “But this is the most compelling evidence that this process is not smooth, simple, and clean, but actually quite chaotic and clumpy.”
Tremblay’s team analyzed data from the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile to map the locations and movement of cold molecular gas in the Abell 2597 Cluster — a knot of about 50 galaxies located 1 billion light years from Earth. The researchers detected a trio of cold gas clouds, traveling as fast as a million kilometers per hour, heading toward a black hole in a galaxy at the center of the cluster. Each gas cloud contained as much material as a million Suns and measured tens of light-years across.
“We can’t know whether all or only part of this ‘meal’ of cold gas will ultimately fall into the black hole, but the ALMA data spectacularly highlights the importance of this kind of cold accretion,” said co-author C. Megan Urry, the Israel Munson Professor of Physics and Astronomy at Yale.
Added co-author Louise Edwards, who is an astronomy lecturer and researcher at Yale: “Since we know so little about the mechanics of how the AGN (active galactic nucleus) interacts with the rest of the galaxy, this is a real step forward.”
Additional data from the National Science Foundation's Very Long Baseline Array indicate that the gas clouds observed by ALMA are approximately 300 light-years from the central black hole, essentially teetering on the edge of being devoured, in astronomical terms.
The researchers said they plan to use ALMA to search for similar “rainstorms” in other galaxies to determine if such cosmic weather is a common phenomenon.
“It was magical being able to see evidence of these clouds accreting onto the supermassive black hole. At that very moment, nature gave us a clear view of this complicated process, allowing us to understand supermassive black holes in a way that has never been possible before," said Timothy Davis of the Cardiff University.
The international team also included researchers from the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research, the Rochester Institute of Technology, Michigan State University, the Harvard-Smithsonian Center for Astrophysics, the Naval Research Laboratory Remote Sensing Division, the University of Michigan, the University of Rochester, and institutions in Germany, the Netherlands, France, Canada, the United Kingdom, and Mexico.
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).