Key points: A team of ~175 astronomers combined Euclid optical and Herschel far‑infrared data to analyze ~2.6 million galaxies and found that average dust temperatures have fallen over billions of years. When the universe was ~3 billion years old, mean dust temperatures were about 35 K (~-238 °C), roughly 10 °C warmer than today. Cooler and less abundant dust corresponds with reduced star formation, indicating the universe has passed its peak era of star‑making. The paper is substantial but has not yet been peer reviewed.
The Universe Is Cooling — New 2.6M‑Galaxy Study Finds Star Formation Is Declining
Key points: A team of ~175 astronomers combined Euclid optical and Herschel far‑infrared data to analyze ~2.6 million galaxies and found that average dust temperatures have fallen over billions of years. When the universe was ~3 billion years old, mean dust temperatures were about 35 K (~-238 °C), roughly 10 °C warmer than today. Cooler and less abundant dust corresponds with reduced star formation, indicating the universe has passed its peak era of star‑making. The paper is substantial but has not yet been peer reviewed.
07:30 PM, 11/15/2025Science
Universe cooling and star formation slowing, large new analysis finds
A broad new analysis combining optical data from the European Space Agency’s Euclid mission with far‑infrared observations from the Herschel satellite shows the cosmos is gradually getting colder and producing fewer stars. The international team — roughly 175 researchers — assembled the largest galaxy sample to date for this kind of study: about 2.6 million galaxies.
Dust temperature is a useful proxy for a galaxy’s star‑forming activity. Massive, young stars heat nearby gas and dust, so more intense star formation tends to produce hotter interstellar dust. Conversely, cooler dust generally indicates lower recent star formation. Supernovae and dying stars also seed galaxies with the heavy elements and dust grains that feed future stellar generations, linking dust content and temperature to a galaxy’s life cycle.
“Dust grains are connected with star formation, and when stars burn up, they make a whole bunch of dust grains in the process,” said Douglas Scott, a cosmologist at the University of British Columbia and a coauthor of the paper.
The researchers report a long‑term decline in average dust temperatures across their sample. When the universe was a little over three billion years old (roughly 10 billion years ago), the mean dust temperature measured about 35 K, which is approximately -238 °C. That value is roughly 10 °C warmer than the average dust temperature the team finds in nearby galaxies today, implying a steady cooling trend over billions of years.
Because dust temperature and amount have both dropped over cosmic time, the study concludes we are past the epoch of maximum star formation. As available cold gas is used up or heated and galaxies evolve, fewer regions reach the conditions needed for vigorous star birth — a trend that, on cosmological timescales, points toward a dimmer, quieter future for stellar production.
Important caveat: the paper has not yet completed formal peer review. Still, the scale of the dataset and its combined optical and far‑infrared approach give weight to the conclusion that the universe’s most active chapter of star formation lies in the past.
This result does not change shorter‑term astrophysical events — stars, supernovae, and galaxy interactions will continue — but it frames those events within a long‑term decline in the global rate of star formation across the cosmos.