These are exhilarating times for physicists delving into the universe’s most profound mysteries, driven by cutting-edge experiments and precise data collection. Particularly intriguing is the enigma of dark energy, the elusive force propelling the universe’s accelerating expansion.
In a groundbreaking report published in the Physical Review Letters, a team of researchers has unveiled new data suggesting that dark energy’s influence on the universe—once thought to be constant—is evolving over cosmic time. The findings, derived from the Dark Energy Spectroscopic Instrument (DESI) at Kitt Peak National Observatory, propose that matter is being transformed into dark energy.
Unveiling the Universe’s Secrets from Kitt Peak
Nestled on Iolkam Du’ag, an isolated mountain in southern Arizona, the Tohono O’odham Nation oversees the Kitt Peak National Observatory, home to DESI. This sophisticated instrument utilizes 5,000 robotic eyes to peer into the universe’s past, each eye focusing on a different galaxy every 15 minutes. Operating nearly every night, DESI has already mapped millions of galaxies, capturing images from a time when the universe was less than half its current size.
The recent study explores the concept of black holes as minuscule bubbles of dark energy. According to the cosmologically coupled black hole (CCBH) hypothesis, black holes—formed when massive stars exhaust their nuclear fuel and collapse—convert stellar matter into dark energy. This theory links the rate of dark energy production and matter consumption to the rate of star formation, a phenomenon observed by the Hubble and James Webb Space Telescopes.
“This paper is fitting the data to a particular physical model for the first time and it works well,” said Gregory Tarlé, a DESI collaboration member and professor emeritus of physics at the University of Michigan.
Neutrinos: The Ghostly Particles
A significant aspect of the study is the mass of neutrinos, the universe’s second most abundant particles. While scientists know these ghost-like particles have mass, their exact values remain elusive. Interpreting the new DESI data through the CCBH model reveals a positive mass measurement, aligning with existing knowledge and improving upon other interpretations that suggested zero or negative masses.
“It’s intriguing at the very least,” Tarlé remarked. “I’d say compelling would be a more accurate word, but we really try to reserve that in our field.”
DESI is an international collaboration involving over 900 researchers from more than 70 institutions, led by Lawrence Berkeley National Laboratory. The project is funded by the U.S. Department of Energy Office of Science and mounted on the U.S. National Science Foundation’s Nicholas U. Mayall 4-meter Telescope at Kitt Peak.
The CCBH Hypothesis: A New Paradigm?
The CCBH hypothesis, introduced five years ago by Kevin Croker of Arizona State University and Duncan Farrah of the University of Hawaii, challenges traditional views of black holes. Instead of “spaghettifying” monsters, black holes are seen as tiny droplets of dark energy influencing the universe. This unconventional idea attracted researchers eager to test its validity against cosmological data.
The hypothesis gained traction with data from DESI’s first year, which showed dark energy density tracking star formation rates. This led Croker and Farrah to collaborate with the DESI team.
“Working with DESI on the three-year data, it’s been a game-changer,” Croker noted. “You’ve got some of the sharpest and most creative researchers in the field lending their hands and hearts. It’s an absolute privilege.”
Neutrinos, alongside photons, are the universe’s most abundant particles. Despite their abundance, neutrinos rarely interact with matter, earning them the moniker “ghost particles.” While experiments on Earth strive to measure their mass, the night sky offers a complementary approach.
DESI’s galactic maps provide insights into the universe’s growth over the past 10 billion years, creating a cosmic inventory of matter and dark energy. Matter comprises cold dark matter, baryons, and neutrinos. Early universe measurements from the Big Bang’s afterglow quantify dark matter and baryons, but DESI suggests a decrease in matter today, leaving little room for neutrinos.
“The data would suggest that the neutrino mass is negative and that, of course, is likely unphysical,” said Rogier Windhorst, Regents’ Professor at ASU’s School of Earth and Space Exploration.
However, when interpreted through the CCBH hypothesis, this issue vanishes. As stars (composed of baryons) die and their matter converts into dark energy, the baryon count decreases, allowing neutrinos to fit the matter budget expected from other measurements.
“You find that the neutrino mass probability distribution points to not only a positive number, but a number that’s entirely in line with ground-based experiments,” Windhorst explained. “I find this very exciting.”
Future Implications and Scientific Scrutiny
While the CCBH hypothesis offers promising insights, it also highlights the interconnectedness of cosmic phenomena. The hypothesis suggests that the conversion of matter to dark energy accelerates the universe’s expansion, aligning the Hubble rate with other measurements like supernovae.
The hypothesis also accounts for the observed amount of dark energy, linking it to star formation. As stars form, the resulting dark energy is proportionate to their number.
“Working on this project has been both challenging and incredibly fun,” said Gustavo Niz, a researcher at the University of Guanajuato, Mexico. “This is just another milestone in establishing CCBH as a viable theory.”
As data continues to pour in, the hypothesis will undergo rigorous analysis and scrutiny. It may become a new paradigm for understanding the universe or be discarded as new evidence emerges.
According to Steve Ahlen, emeritus professor of physics at Boston University, the iterative nature of scientific inquiry is essential. For those involved with DESI, the influx of data is an opportunity to explore novel hypotheses.
“This is so cool, to be at this point after working on an experiment for so long, to be coming up with exciting results,” said Tarlé, who led the team that built DESI’s robotic eye system. “It’s just wonderful.”
DESI’s primary support comes from the DOE Office of Science, with additional backing from various international and national organizations. The collaboration is honored to conduct research on Iolkam Du’ag, a site of cultural significance to the Tohono O’odham Nation.
