First Observational Evidence Linking Black Holes to Dark Energy

(University of Hawaii news release, 15 February 2023)

A team of researchers led by scientists at the University of Hawai’i at Mānoa has 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 published two papers, one in The Astrophysical Journal and another 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 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 absent, 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, lead author of both papers.