New Study Questions Dark Matter’s Cold Origins in the Universe

Research from the University of Minnesota and Université Paris-Saclay challenges the longstanding belief that dark matter emerged cold and sluggish after the Big Bang. Published on January 15, 2026, in the journal Physical Review Letters, the study suggests that dark matter particles may have originated as “red-hot,” moving at nearly the speed of light, before cooling down to contribute to galaxy formation.

For decades, scientists have understood dark matter as a cold substance, a concept rooted in the idea that it must freeze out from a hot, dense state of radiation in the early Universe. This process, known as “freezing out,” has been fundamental in explaining how galaxies and large-scale structures formed. The new research revisits this assumption by focusing on a less-explored period called post-inflationary reheating, which occurred shortly after the Big Bang.

During this phase, the Universe was filled with rapidly moving particles, and researchers examined how dark matter could have been produced in this energetic environment. The findings indicate that dark matter does not necessarily need to start as cold to play its role in cosmic evolution.

Keith Olive, a professor in the School of Physics and Astronomy at the University of Minnesota, elaborated on the implications of this research. He noted that the common candidate for hot dark matter, the low mass neutrino, was dismissed over 40 years ago due to its potential to disrupt the formation of galactic structures. He stated, “The neutrino became the prime example of hot dark matter, where structure formation relies on cold dark matter. It is amazing that a similar candidate, if produced just as the hot big bang Universe was being created, could have cooled to the point where it would in fact act as cold dark matter.”

Prior to this study, fast-moving particles like neutrinos were thought to have smoothed out matter in the early Universe, hindering the formation of galaxies. The researchers now suggest that dark matter could have remained ultrarelativistic during its formation and still slowed down sufficiently over time to allow galaxies to develop.

Lead author Stephen Henrich, a graduate student in the same department, emphasized the significance of these findings. “For the past four decades, most researchers have believed that dark matter must be cold when it is born in the primordial universe. Our recent results show that this is not the case; in fact, dark matter can be red hot when it is born but still have time to cool down before galaxies begin to form,” he stated.

The research team aims to further explore how these hot dark matter particles could potentially be detected. They are considering various methodologies, including direct searches through particle colliders and scattering experiments, as well as indirect detection via astronomical observations. Yann Mambrini, a professor at Université Paris-Saclay, expressed optimism about the future implications of their work, stating, “With our new findings, we may be able to access a period in the history of the Universe very close to the Big Bang.”

Support for this research was provided by the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement. This study not only broadens the understanding of dark matter’s origins but may also pave the way for future discoveries about the fundamental nature of the Universe.