New Research Reexamines Dark Matter’s Origins in Early Universe

New research from the University of Minnesota and Université Paris-Saclay challenges the long-held assumption regarding the nature of dark matter. Published in the journal Physical Review Letters on January 15, 2026, the study suggests that dark matter may have originated as “red-hot,” moving at nearly the speed of light shortly after the Big Bang, rather than the slow-moving cold particles scientists have long assumed.

For decades, the prevailing theory posited that dark matter needed to be cold when it separated from the intense radiation in the young Universe, a process known as “freezing out.” This assumption was thought to be crucial for the formation of galaxies and large-scale cosmic structures. The research team instead focused on a pivotal yet underexplored period in cosmic history known as post-inflationary reheating, during which the Universe rapidly filled with particles following cosmic inflation.

The study unveils a significant shift in understanding. It posits that dark matter particles could have been produced in this energetic phase and subsequently cooled down to become the stable structures we observe today.

Keith Olive, a professor in the School of Physics and Astronomy at the University of Minnesota, emphasized the implications of this research. “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 them,” he explained. This rejection of fast-moving particles like neutrinos had led to the dominance of cold dark matter in scientific discourse.

The study reveals that the high-speed particles need not remain in their initial state. Researchers demonstrated that dark matter could initially exist in an ultrarelativistic state—extremely hot—and still slow down adequately before galaxies began to form. The mechanics of reheating allow for this cooling process to occur as the Universe expands.

Stephen Henrich, lead author of the paper and graduate student at the University of Minnesota, stated, “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.” This revelation opens up new avenues for understanding how dark matter behaves and interacts with other forms of matter.

Looking forward, the research team aims to explore how these hot dark matter particles might be detected. Potential methods include direct searches using particle colliders and indirect detection through astronomical observations. Yann Mambrini, a professor at Université Paris-Saclay and co-author of the paper, remarked, “With our new findings, we may be able to access a period in the history of the Universe very close to the Big Bang.”

The study was supported by funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement. As research continues, the implications of this work may significantly reshape our understanding of the cosmos and the elusive nature of dark matter.