These are exciting times to explore the largest unanswered questions in physics thanks to high-tech experiments and very precise data. That’s particularly true of dark energy, the name given to the mysterious driver of the universe’s accelerating expansion.

In a report published in the Physical Review Letters, a collaboration of researchers has released new data strengthening the case that dark energy’s influence on the universe—long believed to be constant—is actually changing over cosmic time. The team and external collaborators show how the data can be understood as a signal of matter being converted into dark energy.

The new findings stem from an isolated mountain in southern Arizona called Iolkam Du’ag. Here, the Tohono O’odham Nation stewards Kitt Peak National Observatory, where the Dark Energy Spectroscopic Instrument, or DESI, peers deep into the universe’s past using 5,000 robotic eyes—each focused on a different galaxy every 15 minutes.

Working every hour of nearly every night, DESI has already mapped millions of galaxies and other types of ancient, luminous objects, many from when the universe was less than half its current size.

In the current study, the researchers focused on an interpretation of black holes as tiny bubbles of dark energy. Because black holes are made when massive stars exhaust their nuclear fuel and collapse, this cosmologically coupled black hole, or CCBH, hypothesis requires the conversion of stellar matter into dark energy.

This conveniently links the rate of dark energy production, and matter consumption, to something that has been measured for decades by the Hubble Space Telescope and now the James Webb Space Telescope: the rate of star formation.

“This paper is fitting the data to a particular physical model for the first time and it works well,” said DESI collaboration member Gregory Tarlé, professor emeritus of physics at the University of Michigan and corresponding author of the new report.

A major focus of the study is the mass of ghost-like particles called neutrinos, the second most abundant particle in the universe. Scientists know these particles have masses that are greater than zero, and so contribute to the matter budget in the universe, but their exact values have yet to be measured.

Interpreting the new DESI data with the CCBH model gives a measurement greater than zero, in agreement with what scientists already know about these ghost particles and an improvement over other interpretations that prefer zero, or even negative, masses.

“It’s intriguing at the very least,” Tarlé said. “I’d say compelling would be a more accurate word, but we really try to reserve that in our field.”

Uendert Andrade, a Leinweber research fellow at U-M and co-coordinator of DESI’s Year 3 Baryon Acoustic Oscillations analysis team, provided data products and guidance used in the new report. The study’s U-M authors also included Dragan Huterer, a professor of physics, and Michael Schubnell, a research scientist.

DESI is an international experiment that brings together more than 900 researchers from over 70 institutions. The project is led by Lawrence Berkeley National Laboratory, and the instrument was constructed and is operated with funding from the U.S. Department of Energy Office of Science. DESI is mounted on the U.S. National Science Foundation’s Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory—a program of NSF NOIRLab—in Arizona.

Exorcising the ghost particles
The CCBH hypothesis was introduced about five years ago by study co-authors Kevin Croker, assistant research scientist at Arizona State University, and University of Hawaii professor Duncan Farrah. Mathematical descriptions of black holes as tiny droplets of dark energy, instead of “spaghettifying” monsters wrapped in one-way layers, have been explored by researchers for over half a century.

Please continue reading this article on the U-M Michigan News website.

More Information:
Gregory Tarlé
Uendert Andrade
Dragan Huterer
Michael Schubnell

Study: Positive neutrino masses with DESI DR2 via matter conversion to dark energy (DOI: 10.1103/yb2k-kn7h)