Black holes — bodies that warp space-time to such an extent that nothing, not even light, can escape their clutches — are known for their voracious appetites. However, even now, much remains unknown about their feeding habits.
A new study, published Thursday in the journal Nature, sheds further light on what keeps black holes running. The study, based on data collected by the Atacama Large Millimeter/submillimeter Array (ALMA), states that not only do black holes feed on a slow and steady diet of hot ionized gas — which scientists already knew — they also gobble down clumpy, chaotic, very cold clouds of molecular gas.
This, the researchers say, goes a long way toward explaining why many supermassive black holes seem to be much bigger than they should be if they were only chowing down on a slow trickle of hot ionized gas from their host galaxies.
“This so-called cold, chaotic accretion has been a major theoretical prediction in recent years, but this is one of the first unambiguous pieces of observational evidence for a chaotic, cold 'rain' feeding a supermassive black hole,” lead author Grant Tremblay, an astronomer with Yale University in New Haven, Connecticut, said in a statement. “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.”
For the purpose of this study, the researchers trained their sights on a cluster of about 50 galaxies located over 1 billion light-years from Earth — collectively known as the Abell 2597. When they observed the galaxy located in the core of this cluster, they found three massive clumps of cold gas racing toward a supermassive black hole at a breakneck speed of nearly 670,000 miles per hour, with each cloud containing material equivalent to a million suns.
“This very, very hot gas can quickly cool, condense, and precipitate in much the same way that warm, humid air in Earth's atmosphere can spawn rain clouds and precipitation,” Tremblay said in the statement. “The newly condensed clouds then rain in on the galaxy, fueling star formation and feeding its supermassive black hole.”
The results show that black holes, given the right conditions, can binge on large amounts of gas in short bursts, accumulating several solar masses per year. The researchers now plan to observe other galaxies using ALMA for evidence of such “rainstorms.”
“If these 'cold rainstorms' are both long-lived and common in massive galaxies, it might mean that our understanding of black hole growth needs to be reconsidered,” Tremblay told Space.com.