Scientists find first observational evidence linking black holes to dark energy

Dr. Valerio Faraoni of Bishop’s University Department of Physics and Astronomy, has been working with University of Hawaii and a team of 17 researchers across nine countries to develop a description of black holes that agrees with observations from the past decade.

And they’ve hit upon something big.

Searching through existing data spanning nine billion years, the researchers have uncovered the first evidence of “cosmological coupling,” a newly-predicted phenomenon in Einstein’s theory of gravity, possible only when black holes are placed inside an evolving universe.

The team has recently published two papers, one in The Astrophysical Journal and the other in The Astrophysical Journal Letters, that studied supermassive black holes at the hearts of ancient and dormant galaxies. The first paper found that these black holes gain mass over billions of years in a way that can’t easily be explained by standard galaxy and black hole processes, such as mergers or accretion of gas. The second paper finds that the growth in mass of these black holes matches predictions for black holes that not only cosmologically couple, but also enclose vacuum energy—material that results from squeezing matter as much as possible without breaking Einstein’s equations, thus avoiding a singularity.

With singularities removed, the paper then shows that the combined vacuum energy of black holes produced in the deaths of the universe’s first stars agrees with the measured quantity of dark energy in our universe. “We’re really saying two things at once: that there’s evidence the typical black hole solutions don’t work for you on a long, long timescale, and we have the first proposed astrophysical source for dark energy” said Duncan Farrah, University of Hawaii Astronomer and study architect. “What that means, though, is not that other people haven’t proposed sources for dark energy, but this is the first observational paper where we’re not adding anything new to the universe as a source for dark energy: black holes in Einstein’s theory of gravity are the dark energy.”

These new measurements, if supported by further evidence, redefine our understanding of what a black hole is.

The researchers say their studies provide a framework for theoretical physicists and astronomers to further test – and for the current generation of dark energy experiments such as the Dark Energy Spectroscopic Instrument and the Dark Energy Survey – to shed light on the idea. “If cosmological coupling is confirmed, it would mean that black holes never entirely disconnect from our universe, that they continue to exert a major influence on the evolution of the universe into the distant future” said University of Michigan professor and study co-author Gregory Tarlé.

Dr. Valerio Faraoni explains: “This would be the first observational evidence that black holes cannot be described as isolated objects over cosmological time scales, but are somehow affected by the universe they live in. Conversely, the question of the nature of Dark Energy is perhaps the most important puzzle in contemporary physics. It’s 70 per cent of the energy of the universe. Any new and viable potential solution to the Dark Energy problem is going to look very weird at first and here we have observational evidence pointing to one. It’s very exciting!”

Duncan Farrah et al 2023, Observational Evidence for Cosmological Coupling of Black Holes and its Implications for an Astrophysical Source of Dark Energy, The Astrophysical Journal, 943 L31
https://iopscience.iop.org/article/10.3847/2041-8213/acb704

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