QUT cosmologist helps shine light on dark energy
A QUT cosmologist is part of the international research team that today has published an analysis that shines new light on dark energy and suggests the standard model of how the universe works may need an update.
Dr Rossana Ruggeri, from the QUT School of Chemistry and Physics who studies the properties of the universe on the largest scales, is part of the Dark Energy Spectroscopic Instrument (DESI).
DESI is an international experiment with more than 900 researchers from over 70 institutions around the world, including QUT, Swinburne University and the University of Queensland, and is managed by the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).
The project today published a new analysis of dark energy using its first three years of collected data, which spans nearly 15 million galaxies and quasars (extremely distant yet bright objects with black holes at their cores).
Caption: Star trails over the Mayall Telescope that houses DESI. Credit: Luke Tyas/Berkeley Lab
The collaboration shared their findings across multiple papers that will be posted on the online repository arXiv and in a presentation at the American Physical Society’s Global Physics Summit in Anaheim, California
DESI used millions of galaxies and quasars to build the largest 3D map of our universe to date. Combining its data with other experiments shows signs that the impact of dark energy may be weakening over time – and the standard model of how the universe works may need an update.
The fate of the universe hinges on the balance between matter and dark energy: the fundamental ingredient that drives its accelerating expansion.
New results from the DESI collaboration use the largest 3D map of our universe ever made to track dark energy’s influence over the past 11 billion years. Researchers see hints that dark energy, widely thought to be a “cosmological constant”, might be evolving over time in unexpected ways.
Professor Alexie Leauthaud-Harnett, from UC Santa Cruz and co-spokesperson for DESI, said: “What we are seeing is deeply intriguing. It is exciting to think that we may be on the cusp of a major discovery about dark energy and the fundamental nature of our universe.”
Dr Ruggeri is a co-author on the papers related to this announcement and has been involved in the analysis and interpretation of the dark energy results. This work is part of her ARC Discovery Early Career Researcher Award, which aims to address key questions about the nature of dark energy and gravity, and advance our understanding of fundamental physics with tools from astronomy, advanced statistics, and data science.
“This is a major moment for cosmology,” Dr Ruggeri said.
“Dark energy is believed to permeate all of space, causing the accelerated expansion of the universe.
“It makes up about 70 per cent of the universe, but its nature is one of the most significant puzzles in modern physics.
The DESI first-year result papers were among the most cited papers in 2024 in the field of cosmology, and these new results suggest that dark energy may not be constant as previously thought – a potentially big shift in our understanding of the universe.”
Dr. Ruggeri is co-chair of the DESI C3 (Clustering, Clusters & Cross-Correlation) working group, where she leads efforts to combine DESI spectroscopic data with galaxy lensing from major imaging surveys. The goal is to improve constraints on the growth of cosmic structures and test models of gravity by studying how gravity influences the motion of matter and the bending of light.
DESI is one of the most extensive surveys of the cosmos ever conducted. The state-of-the-art instrument can capture light from 5000 galaxies simultaneously, and was constructed and is operated with funding from the DOE Office of Science.
DESI is mounted on the US National Science Foundation’s Nicholas U Mayall four-metre telescope at Kitt Peak National Observatory (a program of NSF NOIRLab) in Arizona. The experiment is now in its fourth of five years surveying the sky, with plans to measure roughly 50 million galaxies and quasars by the time the project ends.
The Dark Energy Spectroscopic Instrument (DESI) operating out of the Mayall 4-meter Telescope Credit: Marilyn Sargent/Berkeley Lab
The new analysis uses data from the first three years of observations and includes nearly 15 million of the best measured galaxies and quasars. It’s a major leap forward, improving the experiment’s precision with a dataset that is more than double what was used in DESI’s first analysis, which also hinted at an evolving dark energy.
Taken alone, DESI’s data is consistent with our standard model of the universe: Lambda CDM (where CDM is cold dark matter and lambda represents the simplest case of dark energy, where it acts as a cosmological constant).
However, when paired with other measurements, there are mounting indications that the impact of dark energy may be weakening over time and other models may be a better fit.
Those other measurements include the light leftover from the dawn of the universe (the cosmic microwave background or CMB), exploding stars (supernovae), and how light from distant galaxies is warped by gravity (weak lensing).
Dr Willem Elbers, a postdoctoral researcher at Durham University and co-chair of DESI’s Cosmological Parameter Estimation working group, which works out the numbers that describe our universe, said there had been a standard model of cosmology for several decades.
“As our data is getting more and more precise, we’re finding potential cracks in the model and realizing we may need something new to explain all the results together,” Dr Elbers said.
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