Astronomers at Maynooth University have explained how supermassive black holes formed quickly after the Big Bang through simulations of chaotic early galaxies. These conditions allowed small black holes to grow rapidly by devouring gas at extraordinary rates. The findings align with observations from the James Webb Space Telescope.
One of astronomy's enduring mysteries—how supermassive black holes reached immense sizes so soon after the universe's birth—may have a solution, according to a study from researchers at Ireland's Maynooth University. Published in Nature Astronomy, the research uses advanced simulations to show that the turbulent, gas-rich environments of early galaxies triggered explosive growth in initial black holes.
The team, led by PhD candidate Daxal Mehta in the Department of Physics, focused on black holes formed just hundreds of millions of years after the Big Bang. "We found that the chaotic conditions that existed in the early Universe triggered early, smaller black holes to grow into the super-massive black holes we see later following a feeding frenzy which devoured material all around them," Mehta explained.
These simulations reveal that so-called light seed black holes, starting at 10 to a few hundred times the Sun's mass, expanded to tens of thousands of solar masses. This occurred via super-Eddington accretion, where black holes ingested matter faster than typical radiation limits would allow, defying previous assumptions that only larger heavy seed black holes—up to 100,000 solar masses from the start—could achieve such scales.
"These tiny black holes were previously thought to be too small to grow into the behemoth black holes observed at the centre of early galaxies," Mehta noted. "What we have shown here is that these early black holes, while small, are capable of growing spectacularly fast, given the right conditions."
The work addresses puzzles from the James Webb Space Telescope, which has spotted massive black holes earlier than expected. "This breakthrough unlocks one of astronomy's big puzzles," said Dr. Lewis Prole, a team member. Leader Dr. John Regan added, "Heavy seeds are somewhat more exotic... Our simulations show that your 'garden variety' stellar mass black holes can grow at extreme rates in the early Universe."
The early cosmos appears more dynamic than thought, with a larger population of such black holes. This could shape expectations for the 2035 Laser Interferometer Space Antenna mission, potentially detecting mergers of these early growers through gravitational waves.