New supernova analysis backs accelerating universe

A new analysis led by the University of Southampton says the universe is still expanding at an accelerating rate, preserving a central finding of modern cosmology. The study challenges a late-2025 claim that evidence for dark energy, the still-unexplained driver thought to be behind that acceleration, had weakened.

The work was published in the Monthly Notices of the Royal Astronomical Society and includes astrophysicists Adam Riess and Brian Schmidt, who shared the 2011 Nobel Prize in Physics with Saul Perlmutter for the discovery that cosmic expansion is speeding up. According to the University of Southampton, the new study finds that current cosmological models remain consistent with the supernova evidence.

The dispute centered on Type Ia supernovae, bright explosions of white dwarf stars that astronomers use as distance markers. By comparing how bright these events appear with how bright they are expected to be, researchers can estimate distances across the universe and trace how cosmic expansion has changed over time.

In late 2025, a group of astronomers argued that standard supernova measurements had serious flaws, according to the University of Southampton. Their analysis suggested that the peak brightness of Type Ia supernovae may shift as the universe ages, raising the possibility that astronomers had mistaken a changing supernova population for evidence of acceleration.

Phil Wiseman, the Southampton astronomer who led the new paper, said the challenge came from a misreading of the data rather than a failure of the underlying measurements. According to Southampton, Wiseman said the accepted measurements hold up and that researchers can return to the problem of identifying what dark energy is, rather than questioning whether the evidence for it exists.

The Southampton-led team concluded that the 2025 analysis treated the age of a galaxy as if it were the same as the age of the star that later exploded as a supernova. The researchers said that assumption distorted the interpretation of the supernova sample.

The team also said the earlier work did not properly include the mass of the host galaxies, a correction that modern cosmology studies commonly use to improve supernova measurements. After applying the relevant calibrations, the researchers found that the evidence for accelerating expansion remained steady.

Riess said, according to the University of Southampton, that claims challenging an established result need especially close testing. He said the supernova evidence for acceleration stays consistent when researchers calibrate the explosions while accounting for different host environments and stellar populations.

The University of Southampton said the 2025 claim, if confirmed, would have called nearly three decades of cosmology into question. Instead, the new paper reports that Type Ia supernova cosmology is robust against the proposed effect linked to host galaxy age evolution.

Mark Sullivan, a Southampton professor and co-author, said the episode still had scientific value because testing accepted ideas can improve methods. According to the university, Sullivan said the failed challenge prompted researchers to think in new ways about supernova explosions and how dark energy measurements can be sharpened.

Co-author Brodie Popovic said the project gave the team a chance to review assumptions behind current cosmology measurements. According to Southampton, Popovic said the review supported the view that researchers understand the relevant supernova effects and account for them in their measurements.

This story draws on original reporting from ScienceDaily.