A new international study has strengthened evidence that the universe’s expansion is still accelerating, challenging earlier claims that questioned one of modern cosmology’s most important discoveries. The study was published in the Monthly Notices of the Royal Astronomical Society.
Type Ia supernova visible as a blue dot at the center of this NASA/ESA Hubble Space Telescope image. Image Credit: ESA/Hubble & NASA, R. J. Foley (UC Santa Cruz)
The study revisits theories suggesting that the evidence for dark energy, the mysterious force thought to drive the universe’s accelerating expansion, might be explained by subtle variations in the properties of Type Ia supernovae, the exploding stars astronomers use as reliable markers for measuring vast cosmic distances.
The team discovered that contemporary cosmological analyses already understand and account for these consequences. The findings demonstrate that the evidence for cosmic acceleration is still quite compelling.
The previous and well-accepted measurements were, in fact, fine and our current understanding of the fate of the Universe remains robust. Thankfully we have averted this crisis, but the mystery about why the Universe is still accelerating remains. By proving our measurements are correct, we can get back to trying to understand what dark energy actually is, rather than wondering if it exists at all.
Dr. Phil Wiseman, Study Lead Author, University of Southampton
The 2011 Nobel Prize in Physics was awarded for the discovery that the universe’s expansion is accelerating, a finding first reported in 1998 through observations of Type Ia supernovae. More recent research has suggested that cosmological measurements could be influenced by differences in the ages of the stars that produce these explosions, potentially weakening, or even eliminating, the evidence for dark energy.
However, the current research shows that the usual corrections used in contemporary supernova cosmology already account for a considerable portion of the projected effect. The study's co-author, Associate Professor Maria Vincenzi of the University of Oxford's Department of Physics, has spent nearly ten years studying Type Ia supernova cosmology.
We have long known that the brightness of Type Ia supernovae depends on the age of the stars that produce them, but measuring those ages directly is incredibly challenging. Instead, we use indirect clues, such as the mass of the galaxies that host these explosions and already take into account for these effects.
Maria Vincenzi, Associate Professor, Department of Physics, University of Oxford
“Extraordinary claims require especially careful testing. What we find is that when we calibrate these supernovae, accounting for different host environments and stellar populations, the evidence for cosmic acceleration remains remarkably consistent,” added Co-author Professor Adam Riess, Nobel Laureate and one of the original discoverers of cosmic acceleration.
Understanding how the environments of Type Ia supernovae affect cosmological measurements and galaxy evolution is a rich field of study and one that we hope will enable us to deepen our greater understanding of the universe. Our recent findings provide further confidence in the cosmological framework that has emerged over the past three decades and allow the research community to focus on one of the biggest unanswered questions in physics: the nature of dark energy itself.
Maria Vincenzi, Associate Professor, Department of Physics, University of Oxford
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Journal Reference:
Wiseman, P., et al. (2026) Still accelerating: type Ia supernova cosmology is robust to host galaxy age evolution. Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stag797. https://academic.oup.com/mnras/article/549/3/stag797/8703725.