An international research team led by scientists from the University of Queensland’s School of Mathematics and Physics analyzed 2,884 Type Ia supernovae. These powerful stellar explosions act as cosmic distance markers, allowing astronomers to trace the history of the universe’s expansion.

PhD candidate Ryan Camilleri said the project could establish a new international standard for supernova cosmology. By combining decades of measurements into one unified data set, the researchers created the most detailed picture yet of how the universe’s expansion has changed over time.

“We have reconstructed 30 years of astronomical observations into a single, coherent framework,” Camilleri said.

“We combined the data with other cosmic measurements, such as the afterglow of the Big Bang and maps showing how galaxies are distributed in the universe.”

“Instead of confirming the standard model of cosmology, which assumes that dark energy is fixed and unchanging, we now have further evidence that dark energy can change over time.”

How 30 years of supernova observations were combined

The new collection combines earlier supernova measurements with results from the Dark Energy Survey (DES), which were published in 2024.

To compare observations gathered during different periods, the scientists used modern analytical techniques to reassess older data. Improved knowledge of supernova behavior allowed the team to make measurements from several decades more consistent and accurate.

“Over the years, we’ve learned more and more about how supernovae behave, so we’ve been able to go back and deepen that understanding and apply it to older data,” Camilleri said.

The researchers also accounted for differences between the telescopes used to collect the observations. Cosmic dust and the mass of a galaxy can affect the light received from a distant supernova, influencing estimates of its distance.

“Extensive work has been done to combine observations from different telescopes with different capabilities and to take into account issues such as cosmic dust and galactic mass that can affect the light coming from supernovae.

“We also incorporate more subtle effects such as gravitational lensing, a phenomenon in which light bends and expands around large objects as it travels from a supernova to Earth.”

Why the findings challenge the standard dark energy model

Astrophysicist Professor Tamara Davis said the expanded data set represented a significant advance in efforts to understand the nature of dark energy.

In 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 can fully explain how the universe’s expansion has evolved.

“The 2024 supernova data from DES gave the first hint that dark energy can be time-varying, and in this new compilation we also see a departure from the standard model, albeit in a slightly different direction,” Professor Davis said.

The result is notable because other astronomical projects have also found evidence suggesting that dark energy may not be constant.

“Similarly, results from the Dark Energy Spectroscopy Instrument (DESI) found hints of changes in dark energy when examining relic sound waves from the early universe.”

“So, with two completely independent measurements, we found hints of time variation in dark energy, challenging the standard model that dark energy is immutable.”

Although the different measurements do not indicate exactly the same deviation from the standard model, they provide further reason to investigate whether dark energy changes as the universe ages.

Could dark energy connect gravity and quantum physics?

Understanding dark energy could have implications beyond explaining the universe’s expansion. The researchers believe that studying its behavior may also provide insight into one of theoretical physics’ biggest unsolved problems: reconciling gravity with quantum physics.

“All of this research may hold clues to explaining how gravitational and quantum physics come together.

“We know that these two theories have been very successful in their respective fields, so if we can find a way to combine them, it would be a huge step in theoretical physics.”

Future supernova surveys could test the result

The researchers plan to expand the data set as new observations become available. One important source will be the Dark Energy Bedrock All-Sky Supernova Program (DEBASS), which has identified hundreds of supernovae closer to Earth than those investigated by DES.

Adding these nearby explosions will provide more measurements for studying the expansion of the universe and testing whether dark energy truly changes over time.

Cosmology Discoveries is available on arXiv. A companion measurement of host-galaxy mass is also available on arXiv.

Decades of international collaboration

The findings are based on decades of research by hundreds of astronomers and researchers worldwide. Contributing projects include the Dark Energy Survey, Foundation Supernova Survey, Pan-STARRS1, Sloan Digital Sky Survey, Supernova Legacy Survey, Carnegie Supernova Project, and the Center for Astrophysics Supernova Survey.