Dark Matter May Have Started Extremely Hot
New research suggests dark matter may have begun much hotter and faster than scientists previously thought. A team from the University of Minnesota Twin Cities and Université Paris-Saclay found that dark matter could have moved near the speed of light in the early Universe.
This discovery offers new clues about the Universe’s origins and broadens our understanding of how dark matter interacts with normal matter.
Rethinking “Cold” Dark Matter
For decades, scientists assumed dark matter had to be cold or slow-moving when it separated from the radiation in the early Universe. Cold dark matter helps explain how galaxies and large-scale structures formed.
Keith Olive, professor at the University of Minnesota, explained that low-mass neutrinos were long considered “hot” dark matter. They were ruled out because they would have prevented galaxy formation.
Dark Matter Cooling Before Galaxies Form
The new study shows that dark matter can start ultrarelativistic, or extremely hot, and still cool down in time for galaxies to form. The key is that dark matter production occurs during a period called post-inflationary reheating, just after the Big Bang.
Stephen Henrich, the study’s lead author, said, “Most researchers thought dark matter had to be cold from birth. Our results show it can start red hot and still act like cold dark matter later.”
Detecting Hot Dark Matter
The researchers now aim to identify ways to detect these particles. They plan to use particle colliders, scattering experiments, and astrophysical observations.
Yann Mambrini, co-author from Université Paris-Saclay, noted, “Our findings may let us study a period of the Universe very close to the Big Bang, giving insight into its earliest moments.”
Implications for Cosmology
This research challenges a long-standing assumption in physics. It opens new possibilities for dark matter models and could reshape how scientists think about the early Universe, galaxy formation, and fundamental particle physics.
