New Study Redefines Dark Matter: From Cold to Hot Origins

Research published on January 15, 2026, by scientists from the University of Minnesota and Université Paris-Saclay challenges the prevailing understanding of dark matter. The study suggests that dark matter particles may have originated as “red-hot,” moving at speeds near that of light, rather than the cold, slow particles previously assumed.

This significant shift in perspective comes from examining a lesser-known phase in cosmic history known as post-inflationary reheating. During this period, the Universe was rapidly filled with energy and particles following the end of cosmic inflation, allowing for new insights into dark matter’s formation and interactions.

Revisiting Long-Standing Assumptions

For decades, the scientific community has operated under the assumption that dark matter must be cold upon its separation from the intense radiation of the early Universe. This process, referred to as “freezing out,” was believed essential for the formation of galaxies and large-scale cosmic structures. The new findings, published in the esteemed journal Physical Review Letters, challenge this long-held notion.

According to Keith Olive, a professor in the School of Physics and Astronomy at the University of Minnesota, “The simplest dark matter candidate (a low mass neutrino) was ruled out over 40 years ago since it would have wiped out galactic size structures instead of seeding it.” This dismissal led to a preference for cold dark matter as the foundational element for cosmic structure.

By focusing on the reheating phase, the researchers discovered that dark matter could have been produced while still ultrarelativistic, meaning it was moving extremely quickly. The cooling process as the Universe expanded could allow these particles to slow down in time for galaxy formation.

Implications for Future Research and Detection

The implications of this research extend beyond theoretical physics. Stephen Henrich, a graduate student and the lead author of the study, emphasized that “dark matter is famously enigmatic.” He noted that for the past four decades, the assumption has been that dark matter must be cold. The new research indicates that “dark matter can be red hot when it is born but still have time to cool down before galaxies begin to form.”

Looking forward, the research team plans to explore methods for detecting these hot dark matter particles. Potential approaches include direct searches using particle colliders and scattering experiments, as well as indirect detection through astronomical observations. Co-author Yann Mambrini, a professor from Université Paris-Saclay, stated, “With our new findings, we may be able to access a period in the history of the Universe very close to the Big Bang.”

This groundbreaking work was supported by funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement. As the scientific community continues to unravel the mysteries of dark matter, these findings may pave the way for new understandings of the Universe’s origins and its complex structure.