The early universe supercharged black hole growth

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 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," says Daxal Mehta, a PhD candidate in Maynooth University's Department of Physics and lead author of the study.

Rapid Growth After the Big Bang

Using advanced computer simulations, the researchers reconstructed how the first black holes behaved shortly after they formed.

"We revealed, using state-of-the-art computer simulations, that the first generation of black holes - those born just a few hundred million years after the Big Bang -- grew incredibly fast, into tens of thousands of times the size of our Sun."

These results help explain puzzling observations made by the James Webb Space Telescope, which has detected massive black holes existing far earlier than many theories predicted.

"This breakthrough unlocks one of astronomy's big puzzles," says Dr. Lewis Prole, a postdoctoral fellow at MU and member of the research team. "That being how black holes born in the early Universe, as observed by the James Webb Space Telescope, managed to reach such super-massive sizes so quickly."

A Black Hole Feeding Frenzy

The simulations point to dense, gas-rich early galaxies as the key driver of this rapid growth. In these environments, black holes experienced brief but intense growth spurts through a process known as 'super Eddington accretion'. This happens when a black hole pulls in matter faster than conventional physics suggests it should be able to.

Under normal conditions, radiation from the infalling material would push gas away. In the early universe, however, black holes somehow continued feeding despite this limit, allowing them to gain mass at extraordinary rates.

This process appears to provide a long missing connection between the universe's first stars and the supermassive black holes seen later at the centers of galaxies.

Rethinking Black Hole Origins

"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," says Daxal Mehta. "What we have shown here is that these early black holes, while small, are capable of growing spectacularly fast, given the right conditions."

Astronomers classify early black holes into two general categories known as 'heavy seed and 'light seed' types. Light seed black holes begin with relatively modest masses, ranging from about ten to a few hundred times the mass of our Sun. To become supermassive, they must grow dramatically over time, eventually reaching millions of solar masses.

Heavy seed black holes, by contrast, are thought to form already large, potentially weighing up to one hundred thousand times the mass of the Sun at birth.

Challenging Longstanding Assumptions

Until now, many scientists believed that only heavy seed black holes could explain the presence of supermassive black holes in the early universe.

"Now we're not so sure," says Dr. John Regan of MU's Physics Department and leader of the research group. "Heavy seeds are somewhat more exotic and may need rare conditions to form. Our simulations show that your 'garden variety' stellar mass black holes can grow at extreme rates in the early Universe."

The findings suggest that the early cosmos was far more turbulent and productive when it came to forming massive black holes than previously assumed.

"The early Universe is much more chaotic and turbulent than we expected, with a much larger population of massive black holes than we anticipated too," says Dr. Regan.

Implications for Future Space Missions

Beyond reshaping theories of black hole formation, the research also has implications for upcoming space observatories. In particular, it could influence what scientists expect to see from the joint European Space Agency-NASA Laser Interferometer Space Antenna (LISA) mission, scheduled for launch in 2035.

"Future gravitational wave observations from that mission may be able to detect the mergers of these tiny, early, rapidly growing baby black holes," says Dr. Regan.

Such detections would offer a powerful new way to study the universe's earliest black holes and confirm whether these rapid growth scenarios played out as the simulations suggest.