The largest collection of exploding white dwarf stars ever compiled is providing fresh evidence that dark energy, the mysterious force responsible for the Universe’s accelerating expansion, may change over time. The findings challenge a central assumption of modern cosmology and could help scientists better understand how the Universe evolves.
An international research team led by scientists at the University of Queensland’s School of Mathematics and Physics brought together observations of 2,884 Type Ia supernovae. These powerful stellar explosions serve as important tools for measuring distances across the Universe, allowing astronomers to trace its expansion history.
PhD candidate Ryan Camilleri said the project establishes a new international standard for supernova cosmology. By bringing decades of measurements into a unified dataset, researchers have created their most detailed picture yet of how cosmic expansion has changed over time.
“We’ve rebuilt 3 decades of astronomical observations into a single, consistent framework,” Mr. Camilleri said.
“We combined our data with other cosmic measurements including relic light from the Big Bang and maps of how galaxies are distributed through space.
“Instead of confirming the standard model of cosmology which assumes dark energy is fixed and unchanging, we have more evidence that dark energy may change over time.”
Combining Three Decades of Supernova Observations
The new collection brings together historical supernova measurements and findings from the Dark Energy Survey (DES) published in 2024.
To make observations collected over different periods directly comparable, the scientists revisited older data using updated analytical methods. Advances in understanding supernova behavior allowed the team to improve the consistency and accuracy of measurements gathered over decades.
“Over the years we’ve learned a lot more about how supernovae behave so we’ve been able to go back and apply that improved understanding to older data,” Mr. Camilleri said.
The researchers also had to account for differences among the telescopes used to collect the observations. Other factors, including cosmic dust and the masses of galaxies, can influence the light astronomers receive from distant supernovae and therefore affect distance measurements.
“Extensive work has been done to link observations from different telescopes with different capacities and take into account issues such as cosmic dust and galaxy mass which can affect the light coming from a supernova.
“We also incorporated more subtle effects such as gravitational lensing, which is the bending and magnification of light around large objects as it travels from a supernova to Earth.”
New Evidence Challenges the Dark Energy Model
Astrophysicist Professor Tamara Davis said the expanded dataset represents an important advance in efforts to understand the nature of dark energy.
Under the standard model of cosmology, dark energy is treated as a constant property of the Universe. However, recent observations have raised questions about whether that assumption fully explains how cosmic expansion has evolved.
“Our supernova data from DES in 2024 first showed hints that dark energy may be time varying, and this new compilation also sees a deviation from the standard model although in a slightly different direction,” Professor Davis said.
The findings are especially interesting because a separate astronomical project has also produced evidence suggesting that dark energy might not remain constant.
“Similarly results from the Dark Energy Spectroscopic Instrument (DESI) found hints of variations in dark energy in its surveys of relic sound waves from the early Universe.
“So, 2 completely independent measurements have found hints of time variation in dark energy, challenging the standard model that dark energy doesn’t change.
Although the different measurements do not point to exactly the same departure from the standard model, they provide additional reasons to investigate whether dark energy changes as the Universe ages.
Could Dark Energy Help Unite Gravity and Quantum Physics?
Understanding dark energy could have implications extending far beyond the expansion of the Universe. Researchers believe that learning more about its behavior might also provide insights into one of the greatest unresolved problems in theoretical physics: reconciling gravity with quantum physics.
“All of this research may also hold the clue to explain how gravity and quantum physics fit together.
“We know these 2 theories are each immensely successful in their own realms, so if we can figure out how to put them together that would be a huge step in theoretical physics.”
Future Supernova Surveys Could Provide More Answers
The researchers plan to expand the dataset as additional observations become available. One important source will be the Dark Energy Bedrock All-Sky Supernova program (DEBASS), which is identifying hundreds of supernovae at distances closer to Earth than those surveyed by DES.
Incorporating these nearby explosions will provide further measurements that scientists can use to investigate the Universe’s expansion and test whether dark energy truly changes over time.
The cosmology findings are available on arXiv here, while the accompanying measurements of host galaxy masses can be found on arXiv here.
International Collaboration Behind the Research
The new results build on decades of work by hundreds of astronomers and researchers worldwide. Contributing projects include the Dark Energy Survey, Foundation Supernova Survey, PanStarrs I, Sloan Digital Sky Survey, Supernova Legacy Survey, Carnegie Supernova Project, and the Center for Astrophysics supernova survey.
