New Research Reveals Hot Dark Matter May Shape Galaxy Formation

A groundbreaking study published on January 15, 2026, challenges the longstanding assumption that dark matter is cold and sluggish. Researchers from the University of Minnesota and Université Paris-Saclay propose that dark matter particles may have originated at incredibly high temperatures, moving near the speed of light shortly after the Big Bang. This new perspective could reshape our understanding of galaxy formation and the nature of dark matter itself.

Historically, scientists believed that dark matter had to be cold when it separated from the intense radiation of the early Universe, a process known as freezing out. Cold dark matter is characterized by its slow movement, a feature thought essential for the formation of galaxies and large-scale cosmic structures. This study, published in Physical Review Letters, reexamines this critical assumption by focusing on a period termed post-inflationary reheating, during which the Universe rapidly filled with particles.

The research team investigated how dark matter could emerge during this high-energy phase and its implications for its later behavior. Keith Olive, a professor in the School of Physics and Astronomy at the University of Minnesota, noted, “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.”

The study suggests that the conventional view of dark matter as a cold substance may not be accurate. Instead, dark matter could have begun its existence as “red-hot,” moving at nearly light speed, before cooling down sufficiently to contribute to galactic formation. The researchers assert that this cooling process is directly connected to reheating, which allows particles to lose energy as the Universe expands.

Lead author Stephen Henrich, a graduate student at the University of Minnesota, explained, “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; dark matter can be red hot when it is born but still have time to cool down before galaxies begin to form.”

The implications of this research extend beyond theoretical physics. The team aims to explore how these hot dark matter particles might be detected, potentially through direct searches using particle colliders or scattering experiments. Indirect detection methods may also involve astronomical observations of cosmic phenomena.

Co-author Yann Mambrini from Université Paris-Saclay emphasized the significance of these findings: “With our new results, we may be able to access a period in the history of the Universe very close to the Big Bang.”

The research was supported by funding from the European Union‘s Horizon 2020 research and innovation program, specifically under the Marie Sklodowska-Curie grant agreement. This innovative study opens new avenues for understanding dark matter, a substance that continues to elude definitive detection and explanation, and reinforces the notion that the conditions of the early Universe may be more complex than previously thought.