The puzzle of the universe created by the evidence of seemingly massive black holes in the very early universe continues to grow. JWST’s observations of such an anomaly, known as J1120+0641, show that previously favored explanations for how these objects could have emitted so much light so soon after the Big Bang are unlikely, prompting astronomers to try again.
JWST’s extraordinary power has allowed astronomers to look at galaxies more distant than any we’ve seen before. The further we look into space, the longer we look back – and we see these things as they were not long after the universe was created. The fact that many of these appear to be larger and more developed than existing structures seems to allow for an explanation of the requirements,
Among these strange objects at the beginning of time are quasars, bright accretion disks surrounding supermassive black holes. The extreme luminosity of these early quasars, allowing for the billions of light years that light has had to travel, is indicative of supermassive black holes.
The superstructure of the universe does not allow black holes to become massive any time soon.
One explanation is that the objects we see are very good at feeding, meaning that black holes are smaller than the quasars they have produced would suggest. This would be a very easy way out of the mess, if it weren’t for the fact that no signs of such feeding have been seen in J1120+0641, suggesting the black hole at its heart is over a billion solar masses.
That doesn’t make J1120+0641 an unusually massive black hole – some are up to 10 billion solar sizes – but it’s still massive enough to be a problem given its age. It is also the first black hole that JWST has observed in a way that could test some explanations that would avoid the need to rethink our models of the universe. J1120+0641 was chosen for the job because in 2019, when it was deployed on JWST, this was a well-known quasar.
Repeated delays to JWST meant the observations did not take place until January 2023, by which time the most distant quasars had been observed, but J1120+0641 was still a viable option. We see it as it was 770 million years after the Big Bang.
Dr Sarah Bosman of the Max-Planck-Institut für Astronomie examined the spectrum of J1120+0641, collected by JWST, and found that it does not appear to be distinguishable from nearby quasars used as markers, other than being surrounded by more intense dust.
The dust may be hotter, but not different, ruling out the explanation that dust anomalies were leading us to supermassive ancient black holes.
“Overall, the new observations only add to the mystery: Early quasars were surprisingly common. No matter what wavelength we see, quasars are almost identical throughout the ages of the universe,” Bosman said in a statement.
We can estimate the mass of a black hole from the light emitted by nearby gas clusters in what is known as the broad line region of the spectrum. These clusters are orbiting the black hole at nearly the speed of light, and the broadband radiation tells us how close, which in turn allows us to calculate the mass of the black hole. Using JWST observations, Bosman and co-authors calculated the mass of J1120+0641 to be 1.52 billion times that of the Sun.
Black holes grow as their massive gravity captures matter around them. However, there is a limit to the speed at which this can occur, known as the Eddington limit, caused by the balance of the external radiation pressure and the internal gravitational pull. There are ways that the limit can be exceeded temporarily, but there are doubts about how long this can be maintained. In recent years, many black holes that seem to reach very large masses have been found, and JWST has greatly increased their number.
If these early supermassive black holes are really the size we think they are, they need to have crossed the Eddington Limit, or started out massive. This is known as the “heavy seed” scenario and requires an explanation of how black holes with masses at least a million times that of the Sun could have appeared before they had any stars.
By definition, these could not have formed the way black holes do now – through the collapse of a very large star. Instead, the most likely explanation is that giant clouds of gas somehow fell directly into the black holes. How this happened, however, is still an unsolved problem.
The research is published in the open access journal Nature Astronomy.
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