Astronomers say a new study confirms that the universe is still expanding at an accelerating rate, resolving a recent challenge to one of the most important discoveries in modern cosmology.
The debate began in late 2025, when a group of astronomers published research suggesting that evidence for dark energy, a mysterious phenomenon thought to be driving the accelerated expansion of the universe, was weakening. Their analysis raises the possibility that the expansion of the universe is no longer accelerating.
The researchers argued that the standard approach of measuring the expansion of the universe using supernovae, the explosive deaths of stars, contains fundamental flaws.
But a new study led by the University of Southampton revisited the data and came to a different conclusion. The researchers say the universe continues to behave as predicted by current cosmological models.
This research Royal Astronomical Society Monthly Noticesincludes Nobel Prize-winning astrophysicists Professor Adam Rees and Professor Brian Schmidt.
New analysis confirms the acceleration of the universe
Lead author Dr Phil Wiseman from the University of Southampton said the controversy that arose after the 2025 theory stemmed from a misunderstanding of the data, rather than an issue with the universe itself.
He added: “Previous widely accepted measurements are indeed good, and our current understanding of the fate of the universe remains robust.
“Thankfully, we have avoided this crisis, but the mystery remains as to why the universe’s size is still accelerating.
“By proving that our measurements are correct, we can go back to trying to understand what dark energy actually is, instead of wondering if it exists at all.”
The discovery that the expansion of the universe is accelerating was originally made by Ries, Schmidt, and American astrophysicist Saul Perlmutter. For their groundbreaking research, the trio won the Nobel Prize in Physics in 2011.
If the 2025 claim had been proven correct, it would have overturned that breakthrough discovery and called into question nearly 30 years of cosmological research.
Professor Adam Rees said: “Extraordinary claims require particularly careful examination.
“What we found is that when we calibrate these supernovae to account for different host environments and populations, the evidence for cosmic acceleration remains surprisingly consistent.”
Reconsidering supernova measurements
To investigate this question, the Southampton research team focused on type Ia supernovae, extremely bright explosions of white dwarf stars that are used as cosmic distance markers throughout the universe.
A 2025 study claimed that the peak brightness of these supernovae changes with the age of the universe. If true, the effect could lead astronomers to erroneously conclude that the universe is accelerating when it is actually slowing down.
A new analysis reveals that the problem lies not in the supernova itself, but in the method used to estimate its age.
The researchers say earlier studies incorrectly assumed that the age of the galaxy was the same as the age of the star that eventually exploded as a supernova.
The researchers also reported that the 2025 analysis did not properly account for the mass of the host galaxy, a standard correction routinely used in modern cosmology to improve measurement accuracy.
Lessons for understanding dark energy
Professor Mark Sullivan from the University of Southampton stressed that questioning accepted ideas is an important part of scientific progress.
He added: “Thus we are making progress. This idea was incorrect, but it opens up new ways of thinking about how supernovae explode and how we can measure dark energy more precisely.”
Co-author Dr. Brody Popovich said the project provided an opportunity to rethink the assumptions that underpin modern cosmology.
He added: “Recently we have been focusing on the astrophysics of explosions and how they affect cosmology.
“This was a good opportunity to go back and look at all of our assumptions. It turns out that indeed, we understand this and take it into account in our cosmological measurements.”
