“Brightest Object In Known Universe" Puffs Itself Up To Look 15 Times Its Actual Size

A giant supermassive black hole (SMBH) that consumes the mass of the Sun a day has been found to be about one-fifteenth of its initially estimated size, which makes its rate of feeding even more inexplicable. As excited as astronomers are about solving one puzzle and having another made clearer, they’re even more enthused about the potential of the technology that made this finding possible. 

The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.

The JWST keeps turning up objects in the distant universe we can’t explain, and one of the oddest is J0529-4351. This is a quasar, an immensely bright accretion disk powered by a supermassive black hole (SMBH). When discovered last year, astronomers described it as the “Brightest object in the known universe”, although a challenger emerged later that year. 

Initial observations of J0529 (as it’s now called) indicated it is almost certainly 3-4 times as bright as any previously identified quasar, and 200 trillion times brighter than the Sun. It was also thought to have a mass about 17 billion times that of the Sun.

Both these aspects represented puzzles for astronomers. On the one hand, there was the question of how such luminosity was possible. Quasar brightness is determined by the speed at which the SMBH is consuming matter, and this seemed impossibly fast. On the other hand, there was the question of how a black hole could have reached such an enormous size so soon after the Big Bang. We’re seeing J0529 as it was around 2 billion years after the universe formed, and our models of black hole formation can’t explain how something could get so big, so fast, even feeding at that rate.

J0529 is an extreme example, but many other quasars have been reported with apparent masses and rates of feeding that defy existing models.

One half of the mystery remains, but astronomers now think they know how J0529 got so big: it’s just faking it, like an animal that blows itself up to far beyond its true size to ward off predators or rivals.

“Despite the quasar’s extreme luminosity, the black hole at its heart was found to have a mass equal to 'only' around one billion suns,” Dr Christian Wolf of the Australian National University said in a statement. “Instead of rapidly rotating as previously presumed, this black hole is belching up the gas it’s feeding on. The gas is being blown away by the ferocious density of light — this is the brightest object in the universe we know of.”

Wolf was part of the team that discovered J0529, but even the mighty JWST couldn’t view it as more than a bright dot. As with other black holes at distances of 12 billion light-years, its mass was estimated based on the color spectrum from that dot. This revealed a range of colors indicating a sharp difference in the red and blue shift of the gas around the black hole.

At this point, astronomers made an assumption, one that they had made with many other black holes that could only be seen in this way. “We had to do guesswork on how the gas was moving in three dimensions,” Wolf told IFLScience. “It was logical to assume it was all caused by the motion in orbit.”

As Newton demonstrated, orbital speed depends on the orbited object’s mass. By establishing the difference in speed between the gas moving towards and away from us, astronomers calculated J0529’s mass at 17 billion solar masses.

A string of advances has allowed astronomers to make the four telescopes of the European Southern Observatory’s Very Large Telescope (VLT) using near-infrared interferometry, something Wolf told IFLScience has been considered 10 years away for 50 years. For all that time, radio telescopes have been combined in a way that gives a resolution as if using a giant dish that stretches across the entire space between the individual instruments. However, replicating this at shorter wavelengths has run into one obstacle after another.

Having finally resolved those problems, the ESO turned its combined instrument on the universe’s brightest object and achieved a hundred times the JWST’s resolution. This revealed that the light is not all coming from gas circling the black hole prior to consumption. Instead, some of it is from a cloud of gas being hurled out by the radiation pressure of the rest. The material in orbit is moving more slowly, at speeds consistent with a 1.2 billion solar mass.

Explaining how black holes could get so big is now much easier for two reasons, Wolf told IFLScience. The obvious one is that if the black holes are far smaller – in this case, about one-fifteenth of the size – there’s a lot less growing to explain. On top of that, formulas for black hole growth are based on size – the bigger an SMBH already is, the faster it can feed. 

Astronomers estimated the ceiling of black hole feeding using the Eddington limit for its mass, although they knew this was approximate. J0529 is proof that the Eddington Limit is not so much approximate as wrong. If a black hole this size can feed this fast, smaller ones could presumably also grow more quickly than expected to get this big.

The flipside is that we now have an even bigger challenge explaining why the Eddington limit is not even remotely a limit for J0529. That, Wolf admitted, is going to take some work.

The fact that J0569 is so much smaller than was estimated doesn’t necessarily mean all the other puzzlingly large early universe quasars have been similarly overestimated. However, Wolf told IFLScience that as a test run for the first use of the combined VLT at full capacity, the team checked out another quasar and got similar results. 

“We published that previously, but it was tentative because the instrument was not fully operational and the difference was not quite as extreme,” Wolf told IFLScience. With the J0529 data, the first example looks far more solid. Now they’re two for two, Wolf expressed confidence that other oversized quasars will prove similar, noting that a submission has been made to use the VLT’s newfound capacity to investigate a much larger sample.

There will be some competition, however, for the VLT’s time. Wolf notes that the stunning resolution demonstrated in this case also means the VLT should be able to observe planets forming around young stars in a way that has been impossible until now. “In the near future, our own creation story will only get more colorful,” co-author Professor Michael Ireland said.

“Optical interferometry used to be science fiction, and suddenly it is reality,” Wolf told IFLScience. That reality could make a great many things happen.

The study has been accepted for publication in Astronomy and Astrophysics. The preprint is available on ArXiv.org.