What To Know
- These cosmic giants, such as the one found at the heart of quasar J1120+0641, challenge our current understanding of black hole growth due to their enormous mass, reaching billions of times that of the Sun, despite an apparent lack of voracious feeding mechanisms.
- One of the most striking examples is the black hole located at the heart of the galaxy J1120+0641observed as it was approximately 770 million years after the Big Bangwhen the Universe was only 5% of its current age.
- The light emissions from these quasars, bright enough to eclipse the combined light of the surrounding stars, exert a radiation pressure that could even limit the amount of matter that can be accreted by the black hole, a phenomenon known as the Eddington limit.
Since its launch, the James Webb Space Telescope (JWST) has opened a new window into the early Universe, allowing astronomers to make unprecedented discoveries. One of the most intriguing is the observation of supermassive black holes in the first billion years after the Big Bang. These cosmic giants, such as the one found at the heart of quasar J1120+0641, challenge our current understanding of black hole growth due to their enormous mass, reaching billions of times that of the Sun, despite an apparent lack of voracious feeding mechanisms.
A discovery and dilemmas
Supermassive black holes observed by the James Webb Space Telescope (JWST) represent a fascinating challenge for astronomers. One of the most striking examples is the black hole located at the heart of the galaxy J1120+0641observed as it was approximately 770 million years after the Big Bangwhen the Universe was only 5% of its current age. With a mass a billion times greater than that of the Sun, these colossal objects pose a real puzzle. According to traditional models, the growth of a black hole to such dimensions requires continuous fusion and accretion processes on time scales of at least a billion years. This implies that supermassive black holes found in such a young Universe have not had enough time to reach their current size by known processes.
The feeding frenzy hypothesis no longer holds
To explain this rapid growth, one hypothesis proposes that these primordial supermassive black holes went through a period of ultra-efficient feeding frenzy. According to this theory, these black holes would have been capable of accreting matter at an exceptionally high rateexceeding the usual limits imposed by standard growth processes. However, JWST observations have shown that primordial supermassive black holes, including the one at the heart of J1120+0641, have accretion disks and tori of gas and dust similar to those of more recent black holes. Imagine rings of material rotating around the black hole, where the material slowly spirals inward to be swallowed up. The similarity between these structures and those observed in more recent black holes then suggests that the feeding processes were not not necessarily more efficient in the early Universethus contradicting the feeding frenzy hypothesis. Furthermore, the light emissions from these quasars, bright enough to eclipse the combined light of the surrounding stars, exert a radiation pressure that could even limit the amount of matter that can be accreted by the black hole, a phenomenon known as the Eddington limit. It suggests that the faster a black hole feeds, the more the radiation pressure increases, pushing the matter away and thus limiting the rate at which the black hole can continue to grow. So how can we explain the presence of these “cosmic monsters”?
This illustration shows a supermassive black hole feeding. How did the first examples of these objects get so big so soon after the Big Bang? Credits: NRAO/AUI/NSF, S. Dagnello
Several hypotheses
One notable difference highlighted by the JWST is the temperature of the dust in the torus surrounding the accretion disk of J1120+0641. At about 1,130 degrees Celsiusit is approximately one hundred degrees higher than that observed around more recent supermassive black holes. This temperature difference could indicate different conditions in the early Universe likely to allow these black holes to grow faster, although the exact mechanisms behind this observation remain to be explored. Astronomers are also exploring new theories. One favored hypothesis is that of massive seeds. According to this theory, the supermassive black holes of the early cosmos would have formed from already considerably massive seedsof the order of one hundred thousand times the mass of the Sun. These could have formed directly with the collapse of extremely massive gas clouds in the early Universe, thereby circumventing the limitations imposed by models of gradual growth through the accretion of matter and the merger of galaxies. In short, the supermassive black holes of the early cosmos, observed thanks to the capabilities of JWST, challenge our understanding of the evolution of galaxies and black holes. Their existence suggests that the processes of formation and growth of the first black holes were more complex and diverse than current models suggest. Details of this work are published in Nature Astronomy.
