Do black holes grow along with the universe? A new study says yes

A new study by theoretical physicists Valerio Faraoni and Massimiliano Rinaldi claims that black holes can expand along with the universe, challenging the assumption that they are immune to the universe's expansion. The study suggests that black holes must expand at the same rate as the universe to avoid a "naked singularity" in their models. The research is published in the arXiv preprint server and is based on mathematical models that explore the fate of black holes formed in the early universe. The study's findings imply that supermassive black holes observed in infant galaxies might not have grown by swallowing gas at the Eddington limit, but rather by expanding with the universe itself.

The study's findings are supported by the fact that black holes in the early universe would have formed when the universe was still young and not yet fully expanded. The researchers used a mathematical model to track the apparent horizon of a black hole and determine whether it expands at the same rate as the universe. The result was that the black hole becomes comoving with the universe, meaning it expands at the same rate as the cosmos. This conclusion has implications for understanding the growth of supermassive black holes and their formation in the early universe.

The study's implications also extend to the observation of supermassive black holes in infant galaxies, which have been found by the James Webb Space Telescope. These black holes appear to have formed just a few hundred million years after the Big Bang, but according to astrophysics textbooks, they should not have been able to grow that large. The study suggests that the observed size of these black holes could be due to the expansion of the universe rather than gas consumption at the Eddington limit. Additionally, the study's findings may help explain the existence of black holes in the "upper mass gap," where stellar evolution suggests they should not exist. The study is testable and could provide evidence to support the claim that black holes expand with the universe.

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