The black hole discovered lurking in Cosmic Dawn is too big to be easily explained. Located at the center of a galaxy called J1120+0641, it tips the scales at a mass well over a billion suns.
Larger black holes exist all around us today. The problem is in when existence of J1120+0641. At less than 770 million years after the Big Bang, it is hard to see how a black hole could have acquired 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 formed. Now, observations using JWST have removed one of these notions. By all measures, J1120+0641 appears “shockingly normal,” leaving open more exotic explanations for the black hole’s mass increase.
The discovery of J1120+0641 was announced back in 2011 and for several years it remained the most distant known quasar galaxy. It’s actually been quite a few years. As far as we knew, J1120+0641 was an outlier, with one possible explanation for its size still on the table.
Quasar galaxies are galaxies that have a central supermassive black hole that is feeding at enormous speed. They are surrounded by a huge cloud of gas and dust that spits down 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 speed is determined by its Eddington limit, beyond which the heated material shines so brightly that the radiation pressure would exceed the force of gravity, pushing the material away, leaving the black hole with nothing to feed on.
Now, black holes can briefly enter super-Eddington accretion, where they break through this limit and absorb as much material as they can before radiation pressure takes effect. 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 of sufficient resolution to perform a detailed analysis of the galaxy’s light and look for signs associated with extreme processes. And to do that, we needed JWST, the most powerful space telescope ever built, optimized for observing these distant regions of space and time.
JWST observed the galaxy in early 2023, and a team led by astronomer Sarah Bosman of the Max Planck Institute for Astronomy in Germany dissected the light it collected to catalog the properties of the material around the black hole: a huge dust torus on its outskirts and a glowing disk swirling around and feeding into the black hole .
This analysis reveals that the black hole is actually feeding quite normally – there is nothing about its accretion that seems significantly different from other, newer quasar galaxies.
One possible explanation for these giant black holes is that extra dust has led astronomers to overestimate their mass. And yet there is no sign of more dust.
This means that J1120+0641 is what it appears to be: a fairly normal quasar galaxy with a black hole that is not absorbing material at super high rates. A black hole and the way it feeds was already relatively advanced by the time we observed it, within a few hundred million years of the Big Bang.
“Overall, the new observations only add to the mystery: the early quasars were shockingly normal,” says Bosman. “Regardless of what wavelengths we observe them at, quasars are almost identical at all epochs of the universe.”
This means that super-Eddington accretion is not the solution to the growth of mysteriously massive black holes at the dawn of time.
Another main explanation is that black holes first formed from fairly large “seeds”. Rather than a slow, gradual process from something the size of a star, this theory proposes that black holes are formed by the collapse of clumps of matter or even extremely massive stars up to hundreds of thousands of times the mass of the Sun. grow ahead.
As we find more and more of these monstrosities 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 epoch in our Universe’s history.
The research was published in Astronomy of nature.