The cosmic enigma created by evidence of seemingly massive black holes in the very early universe continues to deepen. JWST observations of one such anomaly, known as J1120+0641, show that the once-favored explanation for how these objects could emit so much light so quickly after the Big Bang is unlikely, forcing astronomers to try again.
JWST’s incredible power has allowed astronomers to observe more distant galaxies than any we’ve seen before. The further we look into space, the further we are looking back in time – and we are seeing these objects as they were not long after the universe formed. The fact that many of them appear larger and more developed than existing models seems to allow for explanations,
Among these dawning oddities are quasars, extremely luminous accretion disks surrounding supermassive black holes. The intense brightness of those of these early quasars, allowing for the billions of light years that the light has passed, are indicative of very massive black holes.
The dominant model of the universe does not provide a path for black holes to become so large so quickly.
One explanation is that the objects we’re seeing are particularly efficient at feeding, meaning the black holes are smaller than the quasars that produced them. This would be a very convenient way out of the mess, if no sign of such efficient feeding had been observed in J1120+0641, suggesting that the black hole at its heart contains more than a billion masses. solar.
That doesn’t make J1120+0641 the supermassive black hole anomalously large — some are up to 10 billion solar masses — but it’s still big enough to be a problem given its age. It is also the first black hole that JWST has examined in a way that could test several explanations that would avoid the need to rethink our models of the universe. J1120+0641 was chosen for the task because in 2019, when time was being booked on JWST, it was the most distant known quasar.
Repeated JWST delays meant that observations did not occur until January 2023, by which time more distant quasars had been seen, but J1120+0641 was still a suitable choice. We are seeing it as it was 770 million years after the Big Bang.
Dr Sarah Bosman of the Max-Planck-Institut für Astronomie studied the spectrum of J1120+0641, collected by JWST, and found that it appears indistinguishable from relatively nearby quasars used as benchmarks, except surrounded by somewhat hotter dust .
The dust may be hotter, but it’s no different, ruling out the explanation that dust anomalies were leading us to overestimate the masses of ancient black holes.
“Overall, the new observations only add to the mystery: early quasars were remarkably normal. No matter what wavelengths we observe them at, quasars are nearly identical across all ages of the universe,” Bosman said in a statement.
We can estimate the mass of a black hole from the light emitted by nearby clumps of gas in what is known as the broad line region of the spectrum. These clumps are orbiting the black hole at close to the speed of light, and the broad-line radiation tells us how close, which in turn allows us to calculate the black hole’s mass. Using JWST observations, Bosman and coauthors calculate J1120+0641’s mass to be 1.52 billion times that of the Sun.
Black holes grow as their massive gravity grabs the surrounding matter. However, there is a limit to how fast this can happen, known as the Eddington limit, caused by the balance of external radiation pressure and the internal pull of gravity. There are ways the limit can be temporarily exceeded, but there are doubts as to how long this can be sustained. In recent years, many black holes have been found that appear to have reached impossible masses, and JWST has significantly increased their number.
If these early supergiant black holes are indeed the size we think, this requires them to have exceeded the Eddington limit, or to have had a very early start. This is known as the “heavy seed” scenario and requires an explanation of how black holes with masses at least a hundred thousand times that of the Sun could have appeared before there were any stars.
By definition, these could not have formed as black holes do now – through the collapse of very massive stars. Instead, the most likely explanation is that large clouds of gas somehow collapsed directly into the black holes. How this happened, however, remains a problem that has yet to be resolved.
The study is published in the open access journal Nature Astronomy.
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