'Robotic eyes' help researchers explore the Big Bang in reverse
James Webb Space Telescope NIRCam imaging of star-forming protocluster PHz G191.24+62.04 as it looked 11 billion years ago as the universe was approaching the peak of star formation. These early galaxies are among the most active star-forming galaxies observed between 10.5–11.5 billion years ago. Each galaxy seen in this image is therefore producing many black holes, which are converting matter into dark energy, according to the cosmologically coupled black hole hypothesis. This image shows the two "modules" of JWST NIRCam: The leftmost module contains the protocluster and the rightmost module is an adjacent blank field. Each module sees thousands of galaxies. Photo credit: NASA, ESA, CSA, Maria Polletta (INAF), Hervé Dole (Paris), Brenda Frye (UofA), Jordan C. J. D'Silva (UWA), Anton M. Koekemoer (STScI), Jake Summers (ASU), Rogier Windhorst (ASU)
Nearly 14 billion years ago, a mysterious energy sparked the Big Bang, causing the universe to expand rapidly and generating all known matter — a process described by the inflationary universe theory.
This ancient energy shares key traits with today’s dark energy, an enigma that constitutes about 70% of the universe yet remains largely unknown to scientists.
In a new study published in the Journal of Cosmology and Astroparticle Physics, a team of astronomers and physicists from five institutions, including Arizona State University School of Earth and Space Exploration Regents Professor Rogier Windhorst and Assistant Research Scientist Kevin Croker, are strengthening the case that these phenomena are related with recent data from the Dark Energy Spectroscopic Instrument (DESI): five thousand robotic eyes mounted on the Mayall telescope at the Kitt Peak National Observatory on the land of the Tohono O’odham Nation.
“In 1965, Erast Gliner theoretically anticipated the discovery of dark energy and argued that it should be formed when massive stars collapse into black holes,” said Croker, lead author of the team's new study.
"If you ask yourself the question, 'Where in the later universe do we see gravity as strong as it was at the beginning of the universe?' the answer is at the center of black holes," said Gregory Tarlé, professor at the University of Michigan and co-author of the study. "It's possible that what happened during inflation runs in reverse; the matter of a massive star becomes dark energy again during gravitational collapse, like a little Big Bang played in reverse."
"If black holes contain dark energy, they can couple to and grow with the expanding universe, causing its growth to accelerate," Croker said. "We can't get the details of how this is happening, but we can see evidence that it is happening."
Data from the first year of DESI's planned five-year survey shows tantalizing evidence that the density of dark energy increased in time. This provides a compelling clue supporting this idea of what dark energy is, the researchers said, because that increase in time agrees with how the amount and mass of black holes increased in time.
"When I first got involved with the project, I was very skeptical," said Steve Ahlen, professor at Boston University and co-author. "But I maintained an open mind throughout the entire process, and when we started doing the cosmology calculations, I said, 'Well, this is a really nice mechanism for making dark energy.'"
The difference a DESI makes
To search for evidence of dark energy from black holes, the team used tens of millions of distant galaxies measured by DESI. Peering billions of years into the past, these data can be used to determine how fast the universe is expanding with exquisite precision. In turn, these data can be used to infer how the amount of dark energy is changing in time.
The team compared these data to how many black holes were being made in the deaths of large stars across the history of the universe.
"The two phenomena were consistent with each other — as new black holes were made in the deaths of massive stars, the amount of dark energy in the universe increased in the right way," said Duncan Farrah, associate professor of physics at the University of Hawaii and co-author of the study. This makes it more plausible that black holes are the source of dark energy."
This research complements a growing body of literature studying the possibility of cosmological coupling in black holes. A 2023 study that reported cosmological coupling in supermassive black holes within galactic centers, which involved many of the authors on this paper, has encouraged other teams to search for the effect in black holes across all the different places they can be found in the universe.
"Those papers investigate the link between dark energy to black holes by their rate of growth. Our new paper links black holes to dark energy by when they are born," said Brian Cartwright, astrophysicist, co-author and former general counsel of the U.S. Securities and Exchange Commission.
A key difference in the new paper is that the majority of the relevant black holes are younger than those previously examined. These black holes were born in an epoch when star formation — which tracks black hole formation — was well underway, rather than just beginning.
“This occurs much later in the universe and is informed by recent measurements of black hole production and growth as observed with the Hubble and Webb space telescopes,” said Windhorst, co-author and interdisciplinary scientist for the James Webb Space Telescope.
Science demands more avenues of inquiry and observations, and now that DESI is online, this exploration for dark energy is just getting started.
"The next question is where these black holes are and how they have been moving around for the past 8 billion years. Scientists are working to constrain this right now," Croker said.
“This will only bring more depth and clarity to our understanding of dark energy, whether that continues to support the black hole hypothesis or not," Ahlen said. "I think as an experimental endeavor, it's wonderful. You can have preconceived notions or not, but we're driven by data and observations."
Regardless of what those future observations bring, the work happening now represents a sea change in dark energy research, the team said.
"Fundamentally, whether black holes are dark energy, coupled to the universe they inhabit, has ceased to be just a theoretical question," Tarlé said. "This is an experimental question now."
This press release was written by the University of Michigan with contributions from Arizona State University.
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