How do some black holes get so big? The James Webb Space Telescope may have an answer
Usually, the most thrilling black-hole news surrounds the biggest, baddest and most violent voids we can imagine. I'm talking about the supermassive black holes boasting billions of times the mass of the sun; the ones called quasars that eat up surrounding matter and spew out the excess so aggressively they create light patterns that outshine even the galaxies they live in. You know the ones.
However, on Thursday (March 7), scientists released a study that serves as a reminder: The baddie black holes aren't the only ones worth thinking about. With the help of the trusty James Webb Space Telescope, this team identified a population of those luminescent quasars that aren't characteristically enormous. They are quite huge, to be clear, as they are still supermassive black holes — they're just not that huge.
In short, the reason this finding is a big deal is that, for the longest time, scientists haven't been sure as to how some of those quasars reach the giant sizes we observe. We know mind-bendingly massive quasars exist, but it has remained unclear how, precisely, these quasars earn that mind-bending-mass status. Even with the major level of matter they soak up, it's almost like enough time hasn't passed for them to have reached their final form. So, could these newly discovered, littler quasars represent a transitional phase of the behemoths — filling a gap scientists have long been hoping to fill?
"One issue with quasars is that some of them seem to be overly massive, too massive given the age of the universe at which the quasars are observed," Jorryt Matthee, lead author of the study and an assistant professor at the Institute of Science and Technology Austria, said in a statement. "We call them the 'problematic quasars.'"
Supermassive mysteries
The lives of these "problematic quasars" begin with the deaths of massive stars.
When a really massive star nears the end of its life, its intrinsic nuclear fusion processes, by which it turns hydrogen content into helium, starts to wind down. Eventually, such internal fusion fully stops. This is an issue for a star that wishes to fight the grips of death. Once fusion ends, so does the outward pressure that's been keeping the star stable against the inward push of its own gravity for millions, often billions, of years. Ultimately, the star collapses in on itself. It dies an explosive supernova death, and a black hole is born.
Then, if this black hole starts actively feeding on surrounding matter, it eventually becomes a big, bad quasar. Yet, herein lies the issue. What happens in between?
"If we consider that quasars originate from the explosions of massive stars — and that we know their maximum growth rate from the general laws of physics, some of them look like they have grown faster than is possible," Matthee explained. "It's like looking at a five-year-old child that is 2 meters [6.5 feet] tall. Something doesn't add up."
Aha! That's where the team's new, medium-sized black hole discovery comes in. Maybe these smaller quasars represent the missing piece of the problematic-quasar timeline.
"Black holes and [supermassive black holes] are possibly the most interesting things in the universe. It's hard to explain why they are there, but they are there. We hope that this work will help us lift one of the biggest veils of mystery about the universe," Matthee said.
Follow the red dots
Quite cinematically, the researchers say the JWST identified the objects — which the team adorably calls "baby quasars" — in the form of several little red dots.
"While the 'problematic quasars' are blue, extremely bright and reach billions of times the mass of the sun, the little red dots are more like 'baby quasars.' Their masses lie between 10 and 100 million solar masses," Matthee said. "Also, they appear red because they are dusty. The dust obscures the black holes and reddens the colors,"
It's also key to note that the team knows these observed black holes are indeed quasars — aka, they're actively feeding (or at least going to be doing so) — due to the reddish tint as well. The researchers explain that their targets are emitting what're known as "Hα spectral emission lines" with "wide-line profiles." These spectral lines, they say, are given off when hydrogen atoms are heated; the width of the lines can also trace the motion of gas. The wider the base of the line, the higher the gas velocity.
"Thus, these spectra tell us that we are looking at a very small gas cloud that moves extremely rapidly and orbits something very massive like a [supermassive black hole]," Matthee said.
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The natural next step for the team is to investigate these baby quasars in more detail, attempting to truly connect them to their big brother quasars that have been causing a dilemma for scientists' black hole ancestry calculations. Better yet, however, the team is pretty excited in general about the datasets the JWST captured of the region in space it examined. One of the collaborations behind the data, dubbed EIGER for "Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization," wasn't even designed to find the red dots it stumbled upon. "We found them by chance," Matthee said.
"If you raise your index finger and extend your arm completely, the region of the night sky we explored corresponds to roughly a twentieth of the surface of your nail. So far, we have probably only scratched the surface."
A paper on the discovery was published on March. 7 in The Astrophysical Journal.
