ByCharles Q. Choi
Published July 12, 2023
• 8 min read
A giant black hole, roughly nine million times the mass of the sun, may have been discovered from the early ages of the universe. Detected by the James Webb Space Telescope (JWST), it had already formed in the center of a galaxy only about 570 million years after the big bang. The discovery—and others like it that researchers say are likely to emerge soon—may one day help solve the mystery of how these behemoths could have emerged so early in cosmic history.
Over the decades, scientists have detected two kinds of black holes: stellar-mass black holes and supermassive black holes. Stellar-mass black holes are typically five to 10 times the sun’s mass and are thought to arise when giant stars die and collapse in on themselves, then exploding in supernovae and leaving black holes behind. Supermassive black holes, on the other hand, are millions to billions of times the sun’s mass and form the hearts of most, if not all, large galaxies.
One might naturally assume that supermassive black holes were born from stellar-mass black holes that ate and ate until they grew huge. However, astronomers have detected black holes that are more than one billion times the mass of the sun from less than one billion years after the big bang, says Steven Finkelstein, an astrophysicist at the University of Texas at Austin. It remains an enigma how they could have possibly bloated to such enormous sizes in such a brief time.
“This is one of the major problems in modern astronomy,” says Masafusa Onoue, an astronomer at the Kavli Institute for Astronomy and Astrophysics at Peking University in Beijing.
To solve this puzzle, scientists peer at light from long ago in the universe’s 13.7-billion-year history. After traveling for so long, dust can obscure much of this light, making these early black holes extraordinarily faint.
The newfound black hole, found within a galaxy dubbed CEERS 1019, was discovered as part of a deep galaxy survey known as the Cosmic Evolution Early Release Science (CEERS). Along with two other early supermassive black holes, the object was recently reported in a paper reported accepted for publication in the Astrophysical Journal Letters.
As light travels from distant galaxies to Earth, it slowly gets distorted to longer wavelengths and shifted toward the infrared part of the spectrum. The CEERS survey analyzed data from JWST’s highly sensitive infrared instruments to spot ancient black holes too dim for prior telescopes to see.
The astronomers detected CEERS 1019’s black hole by looking for extraordinarily bright galactic cores. Previous research has suggested that these so-called active galactic nuclei (AGN) are likely black holes that unleash vast amounts of energy as matter falls or accretes onto them.
Given how rare scientists had thought early black holes were, “it was truly a surprise to me that the first-year JWST observations discovered a number of active black holes … within the first billion years of the universe,” says Onoue, who did not take part in the new research.
Probing theories of black hole formation
CEERS 1019’s black hole may not only be the earliest one detected so far, but also the smallest yet identified in the early universe. Most black holes spotted from around this era are more than one billion times the sun’s mass. In contrast, CEERS 1019’s black hole is more like the black hole at the center of our Milky Way galaxy, which is only a few million times the sun’s mass.
“It was thought that lower-mass black holes had to exist in early galaxies, but I didn’t think we could find them with these observations,” says Dale Kocevski, a CEERS team member and an astrophysicist at Colby College in Waterville, Maine. “The most surprising thing for me is that JWST has proven to be more sensitive than we could have hoped for.”
The CEERS survey also detected two other black holes that existed one billion and 1.1 billion years after the big bang, within the galaxies CEERS 746 and CEERS 2782, respectively. These are also relative lightweights at about 10 million solar masses.
CEERS 2782’s black hole was relatively easy to spot, as there was no dust obscuring JWST’s view of it, while the bright accretion disk encircling CEERS 746’s black hole was partially clouded by dust, suggesting it might lie within a galaxy that is also furiously pumping out stars, Kocevski explains.
In CEERS 1019, the team detected extremely fast-moving gas, which they believe can only come from the region surrounding a supermassive black hole. “The signature of fast-moving gas we see isn’t extremely strong. We did extensive simulations to quantify our uncertainties, and arrived at a 95 percent confidence that we detect this feature,” he says. “It will be quite easy to increase the significance of this signal with future observations.”
Some scientists suspect the supermassive black holes in the early universe grew from the mergers of smaller constituent parts, and these newfound objects fit that prediction. Still, CEERS 1019’s black hole is big enough already to prove difficult to explain.
One possibility is that the seeds of supermassive black holes were born from the collapse of enormous gas clouds, 10,000 to one million times the mass of the sun, that existed before galaxies did, says Finkelstein, who led the CEERS survey. Another is that they were born from the supernovae of giant stars, he says, ones up to roughly 100 times the sun’s mass, and then grew at surprisingly fast rates.
“Either case tells us something we didn’t know before,” Kocevski says. “If the former is true, we’ve learned something about what came before galaxies. If the latter is correct, it tells us there’s something we still don’t understand about how black holes grow.”
These two models predict different numbers of black holes that should have existed within the first 600 million years after the big bang, says Zoltan Haiman, an astrophysicist at Columbia University in New York, who did not take part in this research. Discovering more could help solve the puzzle.
“What is exciting is that there are certainly more such objects out there to be found, and both increasing the sample size and pushing to earlier times will allow us to hone in on which of these theories are correct,” Finkelstein says.
The hunt for ancient black holes
Other hints of early black holes have begun to crop up as well. One team may have identified an AGN in the galaxy UHZ1 dating back about 450 million years after the big bang, while the JWST Advanced Deep Extragalactic Survey (JADES) may have discovered an active galactic nucleus within the galaxy GN-z11 dating to roughly 430 million years after the big bang, says Kevin Hainline, an astronomer at the University of Arizona in Tucson and a member of the JADES team.
“These records won’t stand for very long. Which is good!” Hainline says. “We’re only seeing the beginning of what is a great wealth of actively growing supermassive black holes in the early universe.”
CEERS also unexpectedly identified 11 remote candidate galaxies that existed when the universe was 470 million to 675 million years old; scientists had theorized that JWST would detect fewer galaxies at such distances. The newfound galaxies are rapidly forming stars and may shed light on galactic evolution throughout cosmic history, the researchers say.
Intriguingly, the early supermassive black holes that prior work spotted all outshone their host galaxies. In contrast, these newfound lightweights were discovered in previously detected galaxies, Haiman says.
“This means that for some reason the situation is reversed—the small black holes are fainter than their host galaxies, whereas by the time they evolve into the bigger ones, they become much brighter than their hosts,” Haiman says. “This requires that the host galaxies grow slower than the black holes and gives us new understanding into the evolution of these objects.”
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