Scientists are a step closer to solving one of the universe’s biggest mysteries as new research finds evidence that two of its least understood components may be interacting, offering a rare window into the darkest recesses of the cosmos.

The University of Sheffield findings relate to the relationship between dark matter, the mysterious, invisible substance that makes up around 85% of the matter in the universe, and neutrinos, one of the most fundamental and elusive subatomic particles. Scientists have overwhelming indirect evidence for the existence of dark matter, while neutrinos, though invisible and with an extremely small mass, have been observed using huge underground detectors.

The Standard Model of Cosmology (Lambda-CDM), with its origins in Einstein’s General Theory of Relativity, posits that dark matter and neutrinos exist independently and do not interact with one another.

New University of Sheffield research published in the Nature Astronomy journal casts doubt on this theory, challenging the long-standing cosmological model. The research detects signs that these elusive cosmic components may interact, offering a rare glimpse into parts of the universe we can’t see or easily detect.

By combining data from different eras, scientists have found evidence of interactions between dark matter and neutrinos that could have affected the way cosmic structures, such as galaxies, formed over time.

The data spans the history of the universe:

• Data regarding the early universe comes from two main sources: the highly sensitive ground-based Atacama Cosmology Telescope (ACT), and the Planck Telescope, a space observatory operated by the European Space Agency (ESA) from 2009 to 2013. Both instruments were specifically designed to study the faint afterglow of the Big Bang.

• Late-universe data comes from a massive catalogue of astronomical observations taken by the Dark Energy Camera on the Victor M. Blanco Telescope in Chile, along with galaxy maps from the Sloan Digital Sky Survey.

Co-author of the study Dr. Eleonora Di Valentino, a Senior Research Fellow at the University of Sheffield, said: “The better we understand dark matter, the more insight we gain into how the Universe evolves and how its different components are connected.

“Our results address a long-standing puzzle in cosmology. Measurements of the early Universe predict that cosmic structures should have grown more strongly over time than what we observe today.

“However, observations of the modern Universe indicate that matter is slightly less clumped than expected, pointing to a mild mismatch between early- and late-time measurements.

“This tension does not mean the standard cosmological model is wrong, but it may suggest that it is incomplete.

“Our study shows that interactions between dark matter and neutrinos could help explain this difference, offering new insight into how structure formed in the Universe."

The findings set a clear path for further testing of the theory using more precise data from future telescopes, Cosmic Microwave Background (CMB) experiments and weak lensing surveys, which use the subtle distortions of light from distant galaxies to map the distribution of mass throughout the universe.

Dr. William Giarè, co-author of the study and former Postdoctoral Researcher at the University of Sheffield, now based at the University of Hawaiʻi, said: “If this interaction between dark matter and neutrinos is confirmed, it would be a fundamental breakthrough.

“It would not only shed new light on a persistent mismatch between different cosmological probes, but also provide particle physicists with a concrete direction, indicating which properties to look for in laboratory experiments to help finally unmask the true nature of dark matter.”