Computer models reveal how early black holes grew so quickly after the Big Bang

For decades, astronomers have grappled with a fundamental question: how did black holes achieve their immense size so rapidly in the early universe? New research from Maynooth University in Ireland, detailed in Nature Astronomy, offers a compelling answer. The study, led by PhD candidate Daxal Mehta, suggests that chaotic conditions in the early universe fueled a rapid growth spurt for these cosmic giants.

Unlocking the Puzzle of Early Black Hole Growth

According to Daxal Mehta, the research team discovered that the turbulent environment of the early universe triggered smaller, initial black holes to grow at an accelerated rate. This growth was driven by a “feeding frenzy,” where these black holes consumed vast amounts of surrounding material. “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,” Mehta stated.

The research team, including postdoctoral fellow Dr. Lewis Prole and research group leader Dr. John Regan, focused on a period when galaxies were dense, gas-rich, and highly turbulent. These conditions, they found, allowed black holes to feed at extreme rates, albeit for relatively short durations.

Light Seeds and the ‘Lottery’ of Growth

Traditionally, astronomers have considered two primary pathways for black hole formation: “heavy seed” black holes, born unusually large, and “light seed” black holes, formed from the collapse of the first stars. Light seeds typically begin at only ten to a few hundred times the mass of the Sun. While many believed that the rapid growth of early supermassive black holes required the presence of these larger “heavy seeds,” the Maynooth University research challenges that assumption.

“Now we’re not so sure,” says Dr. John Regan. “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 simulations suggest that light seeds can, in some cases, experience a period of rapid growth, essentially “winning the lottery” by finding themselves in a particularly favorable environment within a young galaxy.

Super Eddington Accretion and Growth Spurts

The mechanism driving this rapid growth involves brief episodes of “super Eddington accretion,” where black holes consume gas at a rate exceeding theoretical limits. While intense light from the inflowing gas should normally repel further material, the simulations demonstrate that, in the densest and most chaotic regions, gas can continue to pour in, fueling accelerated growth. These early black holes, previously thought too small to become behemoths, are now shown to be capable of spectacular growth given the right conditions.

Implications for Future Research

The findings have significant implications for interpreting observations from the James Webb Space Telescope and for designing future cosmological simulations. The research highlights the importance of accurately resolving gas scales in simulations to understand black hole growth. The team’s work also suggests potential targets for future gravitational-wave astronomy, specifically for the European Space Agency and NASA’s Laser Interferometer Space Antenna mission, scheduled for launch in 2035. Dr. Regan notes that this mission “may be able to detect the mergers of these tiny, early, rapidly growing baby black holes.”

Frequently Asked Questions

What is “super Eddington accretion?”

Super Eddington accretion is when a black hole swallows gas faster than the usual limit, theoretically pushing gas away with intense light, but simulations show gas can still pour in under chaotic conditions.

What is the difference between “heavy seed” and “light seed” black holes?

Heavy seed black holes are born unusually large, while light seed black holes form when the first stars die and can begin at only ten to a few hundred times the mass of the Sun.

How did the researchers test their ideas?

The researchers ran detailed cosmological simulations of early galaxy formation using a moving-mesh code called Arepo, focusing on resolving gas flows near black holes.

Given these new insights into the early growth of black holes, how might our understanding of galactic evolution need to be revised?