New research puts forward compelling new evidence that dark matter interacts with cosmic "ghost particles" called neutrinos. If that is the case, then this interaction could pose a serious challenge for the standard model of cosmology, our current best model of the universe.
Neutrinos earn their spooky nickname due to the fact that as these chargeless and virtually massless particles travel through space at near the speed of light, they barely interact with other particles, ghosting their way through solid objects like planets. In fact, the interactions between these particles and other matter are so rare and fleeting that every second, around 100 trillion neutrinos stream through your body without you feeling a thing. Dark matter is similar; even though it accounts for around 85% of the matter in the universe, whatever comprises dark matter also barely interacts with ordinary matter and light, if at all. In fact, effectively invisible, dark matter can only be inferred due to its interaction with gravity and the effect this has on light and conventional matter.
However, new findings from a team of researchers from the University of Sheffield suggest that a slight interaction, in the form of a minor exchange of momentum, exists between dark matter and neutrinos. That contradicts the so-called "Lambda Cold Dark Matter (LCDM)" model that attempts to explain the universe's structure and evolution, which says that dark matter and neutrinos exist independently and do not interact with each other.
The evidence for this potentially paradigm-shift-inducing suggestion comes from observations of the universe in its current state, conducted by the Dark Energy Camera on the Victor M. Blanco Telescope in Chile, from galaxy maps created by the Sloan Digital Sky Survey, and details of the universe's distant past gathered by both the Atacama Cosmology Telescope (ACT) and the European Space Agency (ESA) Planck Telescope spacecraft.
These observations have revealed that the modern universe is less "clumpy" than it should be. This cosmic conundrum could be explained by interactions between dark matter and neutrinos, which would impact the way cosmic structures like galaxies form and evolve.
"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," team member Eleonora Di Valentino of the University of Sheffield said in a statement. “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," Di Valentino added.
The next step is to test this idea, something that the team thinks is possible using precise observations from future telescopes of a cosmic fossil called the Cosmic Microwave Background (CMB), a leftover from an event in the universe shortly after the Big Bang. Astronomers could also test this theory using a specific effect that objects of great mass have on space, and therefore light, a phenomenon called "gravitational lensing." This would allow them to better measure the distribution of ordinary matter and dark matter.
"If this interaction between dark matter and neutrinos is confirmed, it would be a fundamental breakthrough," team member William Giarè of the University of Hawaii, said. "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."
The team's research was published on Jan. 2 in the journal Nature Astronomy.
