A black hole discovered in Cosmic Dawn is too big to be easily explained. Located at the center of a galaxy called J1120+0641, it tips the scales with a mass of over a billion suns.
Larger black holes exist all around us today. The problem is in when for the existence of J1120+0641. Less than 770 million years after the Big Bang, it is difficult to understand how the black hole had time to accumulate so much mass.
We’ve known about the galaxy and its supermassive black hole for more than a decade, and scientists had ideas about how it came to be. Now, observations using JWST have disproved one of those notions. By all measures, J1120+0641 appears “shockingly normal,” leaving open more exotic explanations for the black hole’s mass gain.
The discovery of J1120+0641 was announced in 2011, and for several years it remained the most distant known quasar galaxy. It was actually a good few years. As far as we knew, J1120+0641 was an aberration, with one possible explanation for its size still on the table.
Quasar galaxies are galaxies that have a central supermassive black hole accreting at enormous speed. They are surrounded by a huge cloud of gas and dust, which they suck up as fast as they can. The friction and gravity around the black hole heats the material, causing it to glow brightly.
But the rate at which a black hole can feed is not unlimited. The maximum stable velocity is determined by its Eddington limit, beyond which the heated material glows so brightly that the radiation pressure would exceed the gravitational pull, pushing the material out and leaving nothing for the black hole to feed on.
Black holes can now briefly enter super-Eddington accretion, where they pass through this boundary and absorb as much material as possible before radiation pressure kicks in. This is one possible explanation for the black hole at the center of J1120+ 0641 and, as we find them in greater numbers, other large black holes lurking in the early universe.
To look for signs of super-Eddington accretion, astronomers needed data with sufficient resolution to perform a detailed analysis of the galaxy’s light, looking for signs associated with extreme processes. And for that we needed JWST, the most powerful space telescope ever built, optimized for peering into these far reaches of space and time.
JWST observed the galaxy in early 2023, and a team led by astronomer Sarah Bosmann of the Max Planck Institute for Astronomy in Germany split the light it collected to catalog the properties of the material surrounding the black hole: a vast dust plume on the outskirts and a glowing disk that spins around and feeds into the black hole.
This analysis reveals that the black hole is actually feeding quite normally – there is nothing in its accretion that looks significantly different from other, newer quasar galaxies.
One possible explanation for these giant black holes is that the extra dust causes astronomers to overestimate their masses. Yet there is no sign of additional dust.
This means that J1120+0641 is what it appears to be: a fairly normal quasar galaxy with a black hole that is not ingesting material at ultrahigh speeds. The black hole and the way it feeds was already relatively mature by the time we observed it, within a few hundred million years after the Big Bang
“Overall, the new observations only add to the mystery: the early quasars were shockingly normal,” Bosman says. “No matter what wavelengths we observe them at, quasars are nearly identical across all epochs of the universe.”
This means that super-Eddington accretion is not the solution to the growth of puzzlingly massive black holes at the dawn of time.
The other leading explanation is that black holes formed from fairly large “seeds” to begin with. Rather than a slow, gradual process from something the size of a star, this theory suggests that black holes formed from the collapse of clumps of matter or even extremely massive stars up to hundreds of thousands of times the mass of the Sun, giving growth a head start.
As we discover more and more of these monsters lurking in the mists of the early universe, this notion seems less outlandish and more like the best possible explanation we have for this mysterious era in our universe’s history.
The study was published in Natural astronomy.
