The formation of ultrarare supermassive black holes, with masses over one billion solar masses, in the first billion years of the Universe is an open question in astrophysics. Brookhaven National Laboratory theoretical physicists Hooman Davoudiasl, Peter Denton, and Julia Gehrlein have developed a model to explain the formation of these primordial giants as well as the nature of another phenomenon: dark matter. Their paper was published in the journal Physical Review Letters.
This artist’s impression shows the evolution of the Universe beginning with the Big Bang on the left followed by the appearance of the Cosmic Microwave Background. The formation of the first stars ends the cosmic dark ages, followed by the formation of galaxies. Image credit: M. Weiss / Harvard-Smithsonian Center for Astrophysics.
“Before galaxies existed, the Universe was hot and dense, and that is well established,” Dr. Denton said.
“How the Universe cooled down to what we observe today is a matter of interest because we don’t have experimental data describing how that happened.”
“We can predict what happened with the known particles because they interact often. But what if there are not-yet-known particles out there performing differently?”
To explore this question, the researchers developed a model for a dark sector of the Universe, where yet-to-be-discovered particles abound and rarely interact.
Among these particles could be ultralight dark matter, predicted to be 28 orders of magnitude lighter than a proton.
“The frequency of interactions between known particles suggests matter, as we know it, would not have collapsed into black holes very efficiently,” Dr. Denton said.
“But, if there was a dark sector with ultralight dark matter, the early Universe might have had just the right conditions for a very efficient form of collapse.”
Recent observations have suggested supermassive black holes formed in the early Universe, much earlier than physicists previously thought.
This finding leaves little time to account for the growth of supermassive black holes.
“We theorized how particles in the dark sector could undergo a phase transition that enables matter to very efficiently collapse into black holes,” Dr. Denton said.
“When the temperature of the Universe is just right, the pressure can suddenly drop to a very low level, allowing gravity to take over and matter to collapse.”
“Our understanding of known particles indicates that this process wouldn’t normally happen.”
Such a phase transition would be a dramatic event, even for something as spectacular as the Universe.
“These collapses are a big deal. They emit gravitational waves. Those waves have a characteristic shape, so we make a prediction for that signal and its expected frequency range,” Dr. Denton said.
Current gravitational wave experiments aren’t sensitive enough to validate the theory, but next-generation experiments may be able to detect signals of those waves.
And based on the waves’ characteristic shape, physicists could then narrow in on the details of supermassive black hole formation.
Until then, the scientists will continue to evaluate new data and refine their model.
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Hooman Davoudiasl et al. 2022. Supermassive Black Holes, Ultralight Dark Matter, and Gravitational Waves from a First Order Phase Transition. Phys. Rev. Lett 128 (8): 081101; doi: 10.1103/PhysRevLett.128.081101
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