The galaxy NGC 2525 is located about 70 million light-years from Earth. It is best known for its supernova SN 2018gv, which was captured by the Hubble Space Telescope, among others, in 2018. The supernova is visible on the left of the image. | Image source: ESA/NASA
With a new look at data on a type of exploding star, a team of researchers says they have confirmed the idea that the universe is expanding at an accelerating rate — the same observation that led to the identification in the 1990s of a mysterious cosmic force called dark energy.
The study’s findings refute research published last year that concluded that this cosmic expansion is no longer accelerating, a discovery that challenges the basic understanding of the universe.
“The universe is still accelerating,” said astrophysicist Brody Popovich of the University of Southampton in England, one of the leaders of the study published this month in the journal Monthly Notices of the Royal Astronomical Society.
The results of the study, conducted by a team including two Nobel laureates, were guided by observations in two different data sets of a type of stellar explosion called a Type Ia supernova in order to calculate vast cosmic distances. These supernovae destroy an object called a white dwarf, which is the dense remains of a low- to medium-mass star at the end of its life cycle.
This type of supernova has proven its value in studying the structure of the universe based on evidence that all such explosions have approximately the same luminosity. Their observed brightness varies depending on their distance from Earth, making them useful as cosmic mile markers.
By measuring the brightness of these supernovae as seen from Earth, scientists can measure the rate at which the universe expands and changes over time. The Big Bang event about 13.8 billion years ago gave rise to the universe, and it has been expanding ever since. Scientists revealed in 1998 that this expansion was accelerating, with an invisible force called dark energy as the supposed cause.
The contents of the universe include ordinary matter — stars, planets, gas, dust, and all the familiar things on Earth — and dark matter and dark energy. Ordinary matter represents an estimated 5% of its content. Dark matter, which is known as the effects of gravity on galaxies and stars, makes up an estimated 27%. Dark energy makes up an estimated 68%.
The authors of the 2025 study, published in the same journal as the new study, concluded that dark energy is weakening and has stopped accelerating the expansion of the universe.
“Over the past decade, a group at Yonsei University has argued that supernova distances must be calibrated differently by calculating the ages of stars that eventually explode, and that an ‘age effect’ can dramatically alter evidence for acceleration. In our study, we found no evidence for the so-called ‘age effect’ in the largest calibrated supernova samples that the cosmology community has used over the past decade,” Reiss said.
Astrophysicist Young-wook Lee of Yonsei University, located in Seoul, was one of the leaders of the 2025 study. Lee defended his team’s findings and said the main arguments presented by the researchers in the new study had “serious methodological flaws or lead to conclusions that are internally inconsistent with their own reasoning.”
The researchers in the new study expressed confidence in their methodology and conclusions that confirm the acceleration.
Published – 17 June 2026 at 02:16 PM IST
