A physical model based on black holes turning matter into dark energy offers a cure to hiccups in understanding the universe
A collaboration involving a Rutgers University-New Brunswick cosmologist, along with hundreds of other researchers and dozens of institutions, is exploring the nature of dark energy, a mysterious driver of the universe's accelerating expansion, aided by high-tech experiments and very precise data.
In a report published in the Physical Review Letters, this collaboration of researchers has released 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 - including Nicolas Fernandez, a postdoctoral associate who is a member of the New High Energy Theory Center at Rutgers-New Brunswick - showed how the data can be understood as a signal of matter being converted into dark energy.
As a researcher in the Department of Physics and Astronomy at the Rutgers School of Arts and Sciences who studies early universe cosmology and particle physics, Fernandez said he and other scientists involved in the study mathematized models to determine "how the math works here, how the physics work."
"I'm a theorist, in a sense, but I know how to work with data," said Fernandez, a Colombian physicist who earned his master's degree from the University of Hawaiʻi at Mānoa and a doctoral degree in cosmology and black holes from the University of California, Santa Cruz. "People understand very well when you're an experimentalist because you're in a lab. But theory is more like art in a sense. It's just you, alone with your thoughts, writing and working through equations and trying to come up with ideas to explain" some of the mysteries of the universe.
He added, "I'm curious about the universe - how the universe came to be. And there's some puzzles that we haven't figured out yet in the physics community. So, what I do is try to come up with ideas to explain, for example, what is dark energy or what is dark matter and how we can use data from experiments to test those ideas."
In his third year as a postdoctoral associate at Rutgers, Fernandez said his role in the study involved making models "and then comparing them to the data and say, 'Oh look, our model predicts this or our model is congruent with the data.' That's my job: Make the model and then compare with the data."
I'm curious about the universe - how the universe came to be. And there's some puzzles that we haven't figured out yet in the physics community.
Nicolas Fernandez
Postdoctoral associate at Rutgers-New Brunswick
Findings from the collaboration stem from an isolated mountain in southern Arizona called Iolkam Du'ag. There, the Tohono O'odham Nation stewards Kitt Peak National Observatory, where the Dark Energy Spectroscopic Instrument, or DESI, "an amazing, marvelous" scientific tool featuring "a bunch of little eyes," Fernandez said.
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, the instrument has mapped millions of galaxies and other types of ancient, luminous objects, many from when the universe was less than half its current size.
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 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 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.
It is amazing that as humans we can make this complicated apparatus to measure all these galaxies, billions of galaxies. How do you measure billions of galaxies? That's hard. And we are doing that, or DESI is.
Nicolas Fernandez
Postdoctoral associate at Rutgers-New Brunswick
Interpreting the new DESI data with the cosmologically coupled black hole 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."
DESI is an international experiment that brings together more than 900 researchers from over 70 institutions. The project is led by members of the 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 in Arizona.
Fernandez said he was honored to be part of "this community of experimentalists and theorists and be able to use their cosmological measurements. Sometimes as a theorist you forget how hard it is to go and measure things. It is amazing that as humans we can make this complicated apparatus to measure all these galaxies, billions of galaxies. How do you measure billions of galaxies? That's hard. And we are doing that, or DESI is. So yeah, that's pretty cool, at least in my opinion."
Now in his third year at the university, Fernandez added he came to Rutgers to be part of the New High Energy Theory Center, "where I have a lot of freedom to pursue what I find interesting in my research.
He added the Rutgers center "offers something rare in academia: the freedom to be genuinely independent in my research, to pursue the cosmological questions that captivate me and to explore ideas that others might consider too unconventional."
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