Study of Nearly 3,000 Supernovas Suggests Dark Energy May Be Changing Over Time

A catalog of almost 3,000 white dwarfs that exploded as type Ia supernovas after pulling material from a companion star indicates that dark energy, the mysterious force accelerating the expansion of the universe, may be changing over time. The findings, posted as a preprint on the repository arXiv and not yet peer-reviewed, combine the catalog with data from the Dark Energy Survey (DES) and back up 2024 results from the Dark Energy Spectroscopic Instrument (DESI) that had suggested dark energy's influence is weakening.

A white dwarf is the collapsed core left behind when a sun-like star runs out of nuclear fuel. About half of sun-sized stars have a companion star, and if the two are close enough, the white dwarf can strip material from its companion until its mass crosses a threshold called the Chandrasekhar limit, triggering a type Ia supernova. These explosions have such uniform brightness that astronomers use them as "standard candles" to measure cosmic distances.

"We've rebuilt three decades of astronomical observations into a single, consistent framework," said team member Ryan Camilleri of the University of Queensland. The team combined the supernova 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," Camilleri said.

Team member Tamara Davis said the group's 2024 DES supernova data first hinted that dark energy might be time-varying, and this new compilation shows a deviation from the standard model too, though in a slightly different direction than DESI's findings. "Two completely independent measurements have found hints of time variation in dark energy, challenging the standard model that dark energy doesn't change," Davis said. The team's supernova catalog will grow further with observations from the Dark Energy Bedrock All-Sky Supernova program (DEBASS), which is detecting hundreds more nearby supernovas than the DES survey did.