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Illustration showing a halo of dark matter around a spiral galaxy. | Photo: Robert Lee (created using Canva)
A new study provides compelling new evidence that dark matter interacts with cosmic “ghost particles” called neutrinos. If so, this interaction could pose a serious challenge to the standard model of cosmology, our best model of the universe so far.
neutrino get their creepy nickname because because these chargeless and virtually massless particles travel through space at close to the speed of light, they barely interact with other particles as they make their way through solid objects such as planets. In fact, the interactions between these particles and other matter are so rare and fleeting that every second about 100 trillion neutrinos pass through your body without you feeling a thing. Dark matter similar; although it accounts for about 85% of the matter in the universe, everything that dark matter includes also interacts little, if at all, with ordinary matter and light. In fact, the virtually invisible dark matter can only be judged by its interaction with gravity and the effect it has on light and ordinary matter.
However, new results from a team of researchers from the University of Sheffield suggest that there is a small interaction between dark matter and neutrinos in the form of a negligible exchange of momentum. This contradicts the so-called “Lambda Cold Dark Matter (LCDM),” which attempts to explain the structure and evolution of the Universe by arguing that dark matter and neutrinos exist independently and do not interact with each other.
Evidence for this proposal, which has the potential to force a paradigm shift, comes from observations of the Universe in its current state made with the dark energy camera on the Victor M. Blanco Telescope in Chile, from maps of galaxies created by the Sloan Digital Sky Survey, and details of the distant past of the Universe collected by both the Atacama Cosmology Telescope (ACT) and European Space Agency (ESA) Planck spacecraft.
These observations showed that the modern Universe is less “lumpy” than it should be. This cosmic mystery can be explained by the interaction between dark matter and neutrinos, which will affect how cosmic structures such as galaxies form and evolve.
“Our results solve a long-standing mystery in cosmology. Measurements of the early Universe predict that cosmic structures should have grown larger over time than what we see today,” team member Eleanor Di Valentino from the University of Sheffield said in a statement. “However, observations of the modern Universe show that matter is slightly less dense than expected, indicating a small discrepancy between early and late measurements. This discrepancy does not mean that the standard cosmological model is wrong, but it may indicate that it is incomplete.
“Our study shows that the interaction between dark matter and neutrinos may help explain this difference, offering new insights into how structure forms in the Universe,” Di Valentino added.
The next step will be to test this idea, which the team believes is possible using precise observations from future telescopes of a space fossil called Cosmic microwave background (CMB), a remnant event in the Universe shortly after the Big Bang. Astronomers could also test this theory using the specific effect that high-mass objects have on space and therefore light, a phenomenon called “gravitational lensingThis would allow them to better measure the distribution of regular and dark matter.
“If this interaction between dark matter and neutrinos is confirmed, it would be a fundamental breakthrough,” said team member William Jare of the University of Hawaii. “Not only will this shed new light on the persistent discrepancy between different cosmological probes, but it will also provide particle physicists with concrete direction by indicating what properties to look for in laboratory experiments to help definitively reveal the true nature of dark matter.”
The team's study was published Jan. 2 in the journal. Natural astronomy.
