Dark matter could explain the earliest supermassive black holes - UNIVERSE

Credit: CC0 Public Domain 

A growing mystery in astronomy is the presence of gargantuan black holes—some weighing as much as a billion suns—existing less than a billion years after the Big Bang. According to the standard theory of black hole formation, these black holes simply should not have had enough time to grow so large. A study led by University of California, Riverside graduate student Yash Aggarwal shows that dark matter decays could be the key to understanding the origin of these cosmic behemoths. Published in the Journal of Cosmology and Astroparticle Physics, the research shows that the energy released from dark matter decay could alter the chemistry of early galaxies enough to cause some of them to directly collapse into black holes rather than forming stars.

The result is timely, since NASA's James Webb Space Telescope continues to observe unusually large black holes in the early universe that could have formed by direct collapse. Astronomers had believed this process requires a coincidence of nearby stars shining onto pre-stellar gas and so expected it to be rare.

Aggarwal's team goes beyond the standard approach by using dark matter—the unknown 85% of the matter in the universe that helps form galaxies. They show that if dark matter decays, it can leak a small amount of its energy into the gas and supercharge the direct collapse rate. Each decaying dark matter particle would only need to inject an amount of energy that is a billion trillionths of the energy of a single AA battery.

"Our study suggests that decaying dark matter could profoundly reshape the evolution of the first stars and galaxies, with widespread effects across the universe," Aggarwal said. "With the James Webb Space Telescope now revealing more supermassive black holes in the early universe, this mechanism may help bridge the gap between theory and observation."

Flip Tanedo, associate professor of physics and astronomy at UCR and Aggarwal's doctoral co-advisor, said ideas related to this work had been bouncing around his group since 2018.

"The first galaxies are essentially balls of pristine hydrogen gas whose chemistry is incredibly sensitive to atomic-scale energy injection," said Tanedo, a co-author on the paper. "These are the properties that we want for a dark matter detector—the signature of these 'detectors' might be the supermassive black holes that we see today."

The research team, which included James Dent of Sam Houston State University in Texas and Tao Xu of the University of Oklahoma, modeled the thermo-chemical dynamics of the gas in the presence of decaying axions and found that a window of dark matter masses between 24 and 27 electronvolts could produce the conditions to seed direct collapse black holes.

Tanedo pointed out that the work stemmed from a series of coincidences that brought the right people together at the right time, including a series of workshops that connected particle physicists, cosmologists, and astrophysicists to discuss the big questions in their field.

"We showed that the right dark matter environment can help make the 'coincidence' of direct collapse of black holes much more likely," he said. 

Provided by University of California - Riverside  

by Iqbal I Pittalwala, University of California - Riverside

edited by Stephanie Baum, reviewed by Robert Egan 

Source: Dark matter could explain the earliest supermassive black holes