One of astronomy’s longest-standing puzzles has been understanding how black holes have grown so large in such a short span of cosmic time. Scientists have long known that supermassive black holes existed surprisingly early in the universe, but how they reached these enormous sizes was unclear. Now scientists from Ireland’s Maynooth University (MU) report a breakthrough explanation in a new study published in Astronomy of nature.
According to the team, the answer lies in the extreme and chaotic conditions of the early universe.
“We found that the chaotic conditions that existed in the early universe triggered the early, smaller black holes to grow into the supermassive black holes we see later after a feeding frenzy that ate up material all around them,” says Daxal Mehta, a PhD student in Maynooth University’s Department of Physics and lead author of the study.
Rapid growth after the big bang
Using advanced computer simulations, scientists have reconstructed how the first black holes behaved shortly after their formation.
“Using state-of-the-art computer simulations, we have revealed that the first generation of black holes – those born just a few hundred million years after the Big Bang – grew incredibly fast, to tens of thousands of times the size of our Sun.”
These results help explain puzzling observations made by the James Webb Space Telescope, which detected massive black holes existing much earlier than many theories predicted.
“This breakthrough unlocks one of the great mysteries of astronomy,” says Dr. Lewis Prole, postdoctoral fellow at MU and member of the research team. “This is how black holes were born in the early universe, as observed by the James Webb Space Telescope, to reach such supermassive sizes so quickly.”
Black holes feed madness
Simulations point to dense, gas-rich early galaxies as a key driver of this rapid growth. In these environments, black holes experienced brief but intense growth in a process known as “super Eddington accretion”. This happens when a black hole pulls in matter faster than conventional physics says it should be able to.
Under normal conditions, radiation from the incident material would push the gas away. In the early universe, however, black holes somehow continued to feed despite this limit, allowing them to acquire matter at extraordinary rates.
This process appears to provide a long-missing link between the early stars of the universe and the supermassive black holes later observed at the centers of galaxies.
Rethinking the origin of the black hole
“These tiny black holes were previously thought to be too small to grow into the supermassive black holes seen at the center of early galaxies,” says Daxal Mehta. “What we have shown here is that these early black holes, even though they are small, are able to grow spectacularly fast under the right conditions.”
Astronomers classify early black holes into two general categories known as “heavy seeds” and “light seeds.” Black holes from light seeds begin with relatively modest masses, ranging from ten to several hundred times the mass of our Sun. To become supermassive, they must grow dramatically over time, eventually reaching millions of solar masses.
In contrast, heavy progeny black holes are thought to form already large, potentially weighing up to a hundred thousand times the mass of the Sun at birth.
Challenging long-term assumptions
Until now, many scientists believed that only black holes with heavy nuclei could explain the presence of supermassive black holes in the early universe.
“We’re not so sure now,” says Dr. John Regan from the MU Department of Physics and head of the research group. “Heavy seeds are somewhat more exotic and may require rare conditions to form. Our simulations show that your ‘garden variety’ black hole stellar matter can grow at extreme rates in the early universe.”
The findings suggest that the early universe was much more turbulent and productive in terms of forming massive black holes than previously thought.
“The early universe is much more chaotic and turbulent than we expected, with a much larger population of massive black holes than we thought,” says Dr. Regan.
Implications for future space missions
In addition to reshaping theories of black hole formation, the research also has implications for future space observatories. In particular, it could affect what scientists expect from the joint mission of the European Space Agency and NASA’s Laser Interferometer Space Antenna (LISA), which is scheduled to launch in 2035.
“Future observations of gravitational waves from this mission may be able to detect mergers of these small, early, rapidly growing baby black holes,” says Dr. Regan.
Such a detection would offer a powerful new way to study the oldest black holes in the universe and confirm whether these rapid growth scenarios played out as the simulations suggest.
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