Maynooth University team answers question on mystery of black holes
Ellen O'Donoghue
A black hole mystery has been unlocked by Maynooth University researchers.
An answer to the question of how black holes get so big, so quickly, has been provided and reported on in Nature Astronomy.
"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,” Daxal Mehta, a PhD candidate in MU’s Department of Physics, who led the research, said.
The researchers 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 the sun.
“This breakthrough unlocks one of astronomy’s big puzzles,” Dr Lewis Prole, a postdoctoral fellow at MU and research team member, said.
“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.”
The dense, gas-rich environments in early galaxies enabled short bursts of "super Eddington accretion", a term used to describe what happens when a black hole "eats" matter faster than what's normal or safe.
So fast, that it should blow its food away with light, but somehow keeps eating it anyway.
The results have provided a missing link between the first stars and the "supermassive" black holes that came much later.
"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 said.
"What we have shown here is that these early black holes, while small, are capable of growing spectacularly fast, given the right conditions," he added.
Black holes come in heavy seed and light seed types.
The light seed types are relatively small to begin with, only about 10 to a few hundred times the mass of Earth's sun at most, and must grow from there to become supermassive, or millions of times the mass of the sun.
The heavy types start life already much more massive, perhaps up to 100,000 times the mass of the sun at birth.
Up until now, astronomers thought that heavy seed types were required to explain the presence of the super-massive black holes found to reside at the centre of most large galaxies.
"Now we're not so sure," Dr John Regan, of MU’s Physics Department and research group leader, said.
“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 early Universe is much more chaotic and turbulent than we expected, with a much larger population of massive black holes than we anticipated too,” Dr Regan said.
The results will also have implications for the joint European Space Agency-NASA Laser Interferometer Space Antenna (LISA) mission, scheduled to 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,” Dr Regan said.
