Dark matter decays could be the missing ingredient explaining how giant black holes formed before the first stars
Image Credit: Scientific Frontline
Scientific Frontline: Extended "At a Glance" Summary: Decaying Dark Matter and Early Supermassive Black Holes
The Core Concept: The decay of dark matter particles in the early universe may have released sufficient energy to alter the chemistry of primordial gas clouds, causing them to collapse directly into supermassive black holes instead of forming stars.
Key Distinction/Mechanism: Standard astrophysical models suggest black holes form from the collapse of individual stars and grow slowly over time, a timeline that cannot account for the massive scale of the earliest known black holes. This new mechanism posits that decaying dark matter particles (specifically axions) inject trace amounts of energy into pristine hydrogen gas, supercharging the direct collapse rate without requiring the historically assumed, and statistically rare, presence of nearby stellar radiation.
Major Frameworks/Components:
- Direct Collapse Black Holes (DCBH): A theoretical pathway where massive clouds of primordial gas bypass the star-formation phase and collapse directly into a black hole.
- Axion Dark Matter Decay: A specific dark matter model utilizing particles with masses between 24 and 27 electronvolts, which release billion-trillionths of an energy unit upon decay.
- Thermo-Chemical Dynamics: The analysis of how microscopic energy injections from dark matter alter the thermodynamic evolution and cooling processes of pristine hydrogen gas.
Branch of Science: Astrophysics, Cosmology, and Particle Physics.
Future Application: This framework establishes a method to use the first galaxies as macroscopic "dark matter detectors." By observing the distribution and formation rates of early supermassive black holes via the James Webb Space Telescope, astrophysicists can potentially isolate and identify the elusive physical properties of dark matter.
Why It Matters: This research bridges a critical gap between theoretical physics and observational astronomy. It provides a mathematically viable explanation for a major cosmic mystery: how gargantuan black holes—some possessing the mass of a billion suns—could successfully form and exist less than a billion years after the Big Bang.
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 trillionth 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 coauthor 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 black holes much more likely,” he said. “In the same way, the support for interdisciplinary work helped make the ‘coincidence’ leading to this work possible.”
Funding: The research was supported by the National Science Foundation and a UCR Hellman Fellowship.
Published in journal: Journal of Cosmology and Astroparticle Physics
Title: Direct collapse black hole candidates from decaying dark matter
Authors: Yash Aggarwal, James B. Dent, Philip Tanedo, and Tao Xu
Source/Credit: University of California, Riverside
Reference Number: asph041526_01
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