Like any object, black holes take time to grow and form. And like a 6-foot-tall toddler, fans of oversized black holes were too big for their age—the universe wasn’t yet old enough for them to amass billions of suns in weight. To explain these oversized toddlers, physicists had to consider two unpleasant options.
The first was that fan galaxies were initially filled with normal black holes of about the stellar mass that supernovae often leave behind. These then grew both by merging and by swallowing surrounding gas and dust. Normally, when a black hole eats aggressively enough, a burst of radiation pushes its fragments away. This stops the feeding frenzy and sets a speed limit on the growth of black holes, which scientists call the Eddington limit. But it’s a soft blanket: a constant stream of dust could potentially overcome the radiation output. However, it’s hard to imagine such “super-Eddington” growth lasting long enough to explain beasts to fans – they should have accumulated unimaginably quickly.
Or perhaps black holes of impossibly large sizes can form. Gas clouds in the early universe may have collapsed directly into black holes weighing many thousands of suns, creating objects called heavy seeds. This scenario is also difficult to tolerate, since such large, clumpy gas clouds should collapse into stars before a black hole forms.
One of JWST’s priorities is to assess these two scenarios by looking into the past and capturing the fainter ancestors of fan galaxies. These precursors would not necessarily be quasars, but rather galaxies with slightly smaller black holes on the way to becoming quasars. With JWST, scientists have the best chance of discovering black holes that have just begun to grow – objects that are young enough and small enough for researchers to determine their birth weight.
That’s one reason why a group of astronomers from the Cosmic Evolution Early Release Science Survey (CEERS), led by Dale Kocevski of Colby College, worked overtime when they first spotted signs of the emergence of such young black people in the days after Christmas noticed holes.
“It’s kind of impressive how many of them there are,” he wrote Jeyhan Kartaltepean astronomer at the Rochester Institute of Technology, during a discussion on Slack.
“Lots of little hidden monsters,” Kocevski replied.
A growing crowd of monsters
A few galaxies that might be hiding small black holes—the little monsters—immediately jumped out in the CEERS spectra. Unlike their more vanilla siblings, these galaxies emitted light that did not arrive with just one clear hue for hydrogen. Instead, the hydrogen line was blurred or broadened into a range of hues, suggesting that some light waves were squeezed as orbiting gas clouds accelerated toward JWST (much like an approaching ambulance emits an intensifying whine as its siren’s sound waves compress). ), while other light waves were squeezed. Waves were stretched while clouds flew away. Kocevski and his colleagues knew that black holes were pretty much the only object capable of throwing hydrogen around in this way.
“The only way to see the broad component of the gas orbiting the black hole is to look directly into the interior of the galaxy and directly into the black hole,” Kocevski said.
By the end of January, the CEERS team had managed to release a preprint describing two of the “hidden little monsters,” as they called them. The group then set out to systematically survey a larger area of the hundreds of galaxies their program had collected to find out how many black holes there were out there. But just a few weeks later they were overtaken by another team led by Yuichi Harikane from the University of Tokyo. Harikane’s group searched 185 of the most distant CEERS galaxies and 10 found with broad hydrogen lines – the likely work of central black holes with a million solar masses at redshifts between 4 and 7. Then in June an analysis of two other surveys led by Jorryt Matthee the Swiss Federal Institute of Technology in Zurich identified 20 more “small red dots” with broad hydrogen lines: Black holes swirl around redshift 5. An analysis Published in early August announced another dozen, some of which may even grow through merger.