Supernova 1994D (SN1994D) in galaxy NGC 4526

Black holes are dark energy

Anatomy of a black hold — This artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc. This thin disc of rotating material consists of the leftovers of a Sun-like star which was ripped apart by the tidal forces of the black hole. The black hole is labelled, showing the anatomy of this fascinating object.

A team of scientists at the University of Hawaiʻi at Mānoa has made a groundbreaking discovery in their search for evidence of a newly predicted phenomenon in Einstein’s theory of gravity called “cosmological coupling.” Their research, spanning 9 billion years, involved the study of supermassive black holes in elliptical galaxies, which are believed to be the final result of galaxy collisions.

The team’s findings, recently published in The Astrophysical Journal and The Astrophysical Journal Letters, suggest that the combined vacuum energy of black holes produced in the deaths of the universe’s first stars matches the measured quantity of dark energy in the universe. The researchers propose that black holes in Einstein’s theory of gravity are dark energy, providing a new astrophysical source for it. These new measurements, if supported by further evidence, will redefine our understanding of what a black hole is.

Searching for “cosmological coupling”

The team found a way to use measurements of black holes to search for “cosmological coupling.” “Cosmological coupling” is a phenomenon predicted by Einstein’s theory of gravity, but it can only exist when black holes are located inside an evolving universe. Black holes are really hard to observe because they’re super small and very far away, and observations can only be made over a few seconds or tens of years at most. To see how black holes change over billions of years is a big task.

Energy distribution in the Universe according to Planck probe measurements

So, to figure out how black holes have changed over billions of years, the team decided to look at elliptical galaxies. These galaxies are enormous and formed early in the universe, and they contain supermassive black holes. By studying only elliptical galaxies with no recent activity, the team could see how the masses of the central black holes changed throughout the past 9 billion years.

The researchers found that the further back in time they looked, the smaller the black holes were in mass, relative to their masses today. These changes were big: The black holes were anywhere from 7 to 20 times larger today than they were 9 billion years ago. If mass growth of black holes only occurred through accretion or merger, then the masses of these black holes would not be expected to change much at all. However, the researchers suspected that the black holes gained mass by cosmological coupling.

Image Credits

In-Article Image Credits

Anatomy of a black hold via Wikimedia Commons by European Southern Observatory with usage type - Creative Commons License. May 12, 2022
Supernova 1994D (SN1994D) in galaxy NGC 4526 via Wikimedia Commons by NASA/ESA with usage type - Creative Commons License. May 25, 1999
Energy distribution in the Universe according to Planck probe measurements via Wikimedia Commons with usage type - Creative Commons License. April 1, 2013