Type Ia supernovae are powerful stellar explosions that occur when a white dwarf is pushed into a thermonuclear runaway. Because their brightness can be standardized, astronomers use them as reliable cosmic distance markers to trace how the universe has expanded over time. Credit: Shutterstock

Nearly 3,000 exploding stars have revealed a startling possibility: the mysterious force accelerating the universe may be changing over time.

The largest catalog of Type Ia supernovae assembled so far is giving astronomers a more detailed record of cosmic expansion. The results add to evidence that dark energy, the unknown component believed to drive that expansion, may evolve rather than remain constant.

Type Ia supernovae occur when white dwarf stars undergo thermonuclear explosions. Because their brightness can be standardized, astronomers use them as cosmic distance markers, comparing how bright they appear with how quickly their host galaxies are receding. Similar observations helped reveal the accelerating expansion of the universe in the late 1990s.

Three Decades of Supernova Observations

An international effort led by the University of Queensland’s School of Mathematics and Physics compiled measurements from 2,884 Type Ia supernovae. PhD candidate Ryan Camilleri said the collection establishes a new benchmark for supernova cosmology and provides the clearest reconstruction 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.”

Bringing Different Telescopes Into Alignment

The catalog incorporates historic measurements alongside observations from the Dark Energy Survey (DES) published in 2024. Instead of simply combining the original results, the researchers reanalyzed older observations with modern techniques so that data gathered by different telescopes could be compared more reliably.

“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.

“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.”

Independent Clues About Changing Dark Energy

Astrophysicist Professor Tamara Davis said the expanded collection represents an important step toward identifying what dark energy is and how it behaves. Although the latest deviation does not point in exactly the same direction as the earlier DES result, both raise questions about the standard assumption that dark energy remains unchanged.

“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.

“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.”

A Possible Bridge Between Fundamental Theories

Two independent methods now suggest that dark energy may change over time. Supernovae and the ancient sound wave patterns mapped by DESI trace the universe’s expansion across different periods of cosmic history.

“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.”

The catalog will continue to grow as new surveys produce additional observations. Future additions will include data from the Dark Energy Bedrock All-Sky Supernova program (DEBASS), which is finding hundreds of supernovae closer to Earth than those studied by the DES survey.

References:

“Supernovae Unite: Combining Pantheon+ and DES-SN5YR” by Ryan Camilleri, Jaemyoung Lee, Tamara Davis, David Rubin, Paul Shah, Dan Scolnic, Chris Lidman, Brodie Popovic, Koby Grech, Maria Vincenzi, Dillon Brout, Maria Acevedo, Patrick Armstrong, Bruce Bassett, Keith Bechtol, Rebecca Chen, Herman Diehl, Josh Frieman, Lluís Galbany, Anais Möller, Masao Sako, Bruno Sánchez, Mark Sullivan and Brad Tucker, September 8, 2026, arXiv.
arXiv: 2609.05053

“Supernovae Unite: Host-Galaxy Mass Measurements of Type Ia Supernovae and Their Impact on Cosmology” by J. Lee, R. Camilleri, T. M. Davis, D. Rubin, K. Bechtol, L. Galbany, M. Sako, M. Sullivan, T. E. Müller-Bravo, D. Scolnic, M. Vincenzi, D. Brout, C. Lidman, A. Möller, P. Shah, M. Acevedo, P. Armstrong, B. A. Bassett, R. C. Chen, H. T. Diehl, J. Frieman, K. Grech, B. Popovic, B. O. Sánchez and B. E. Tucker, September 8, 2026, arXiv.
arXiv: 2609.05321

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