The standard model of cosmology assumes dark energy never changes. It treats it as a constant that has pushed the Universe apart with the same strength since the start. A new catalog of 2,884 exploding stars suggests that assumption could be wrong.
The catalog is the biggest set of Type Ia supernovae ever put together. According to its builders, it adds new evidence that dark energy, the force behind the Universe’s accelerating expansion, may vary over time.
Two independent projects show the same hint
A single strange result could be chance. This is the second one.
Professor Tamara Davis, an astrophysicist on the team, said the first signs came from the group’s own earlier research. “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,” Davis said.
A different instrument, using a different technique, points in the same direction. “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,” Davis said.
“So, 2 completely independent measurements have found hints of time variation in dark energy, challenging the standard model that dark energy doesn’t change.”
The wording matters here. The two measurements disagree on exactly how the Universe strays from the standard model, and no one is announcing a confirmed discovery. The researchers’ claim is that the question needs closer study. That is a smaller claim than the headlines this sort of research usually gets.
Exploding white dwarfs as measuring sticks
A Type Ia supernova is the explosion of a white dwarf star. Astronomers use these events to measure distances across the Universe. With enough of those distances, they can reconstruct how expansion has unfolded across cosmic history.
Scientists at the University of Queensland’s School of Mathematics and Physics led the international team. They merged historical supernova measurements with Dark Energy Survey (DES) results published in 2024.
According to PhD candidate Ryan Camilleri, the project sets a new international standard for supernova cosmology. “We’ve rebuilt 3 decades of astronomical observations into a single, consistent framework,” 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.”
Reconciling 30 years of inconsistent data
Combining decades of observations is harder than it sounds. The older measurements were taken with different telescopes and processed using older assumptions about supernova behavior.
The team reprocessed them. “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,” Camilleri said.
Both cosmic dust and the mass of a host galaxy can alter the light that reaches Earth from a far-off explosion, and that throws off the distance calculated from it. The team adjusted for both, as well as for differences between instruments.
“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,” Camilleri said.
“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.”
The cosmology results are on arXiv, along with a companion set of host galaxy mass measurements. Hundreds of astronomers built the dataset over decades. It draws on 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.
A longer shot: linking gravity and quantum physics
Davis said the work matters for more than the Universe’s expansion rate. Understanding dark energy’s behavior could help with one of the oldest open problems in theoretical physics.
“All of this research may also hold the clue to explain how gravity and quantum physics fit together,” Davis said.
“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.”
That goal is distant. The nearer test is more data. The team plans to add supernovae from the Dark Energy Bedrock All-Sky Supernova program (DEBASS), which is detecting hundreds of explosions closer to Earth than the ones DES observed. Those nearby supernovae will give the researchers a second set of measurements to check whether dark energy really changes over time.