Time once more for a story of issues darkish and mysterious. A story of darkish matter. It is a well-told story, however this time it entails an interactive dance between darkish matter and neutrinos.
Darkish matter is, in fact, nearly all of matter within the cosmos in response to the usual mannequin and, by definition, can not work together strongly with gentle. There was some debate as to whether dark matter interacts with itself, however to date there is not sturdy proof to recommend that it does. Neutrinos additionally do not work together strongly with gentle. Technically, neutrinos meet the situations of darkish matter, however neutrino particles zip round so shortly that they’re a scorching type of darkish matter. However observational proof we’ve for darkish matter means that it’s chilly. So neutrinos aren’t the darkish matter we’re in search of.
On condition that neither neutrinos nor chilly darkish matter work together strongly with matter, there hasn’t been a lot to recommend that they work together with one another. However a brand new research argues that they do. The authors even recommend that these interactions would assist resolve the Hubble tension problem.
The interplay mannequin straddles the vary between conflicting cosmological knowledge units. Credit score: Zu, et al.
The research checked out an impact often called cosmic shear. It is a delicate distortion in the best way galaxies gravitationally lens distant gentle. If a galaxy have been completely spherical, then the lensing of distant objects can be round. However since galaxies aren’t completely round, the lensed gentle is distorted. For a person galaxy this doesn’t suggest a lot, however galaxies inside a big construction of galaxies have an intrinsic alignment, and this offers a slight alignment or shear to lensed objects. By making giant surveys of gravitationally lensing galaxies, we will measure the cosmic shear and perceive the large-scale construction of the Universe.
The secret is that if neutrinos and darkish matter work together, this could have an effect on the big scale buildings of galactic clusters and voids, which might influence our measure of cosmic shear. Utilizing cosmic shear knowledge gathered by the 3-year Darkish Vitality Survey gathered by the Blanco Telescope in northern Chile, the authors discovered an interplay degree of about 1 half in 10,000. Whereas this means there’s an interplay between the 2, the statistical significance of their result’s solely 3σ, which is not sturdy sufficient to be thought-about proof.
Future cosmic shear surveys, comparable to ones that may be accomplished with Rubin Observatory knowledge, will quickly permit the staff to slim issues down. If new observations affirm their outcomes, we should re-examine our commonplace comsological mannequin. But it surely’s additionally potential that the information will not maintain up, and this concept will be part of the multitude of others that give us prospects however no solutions. For now the darkish thriller continues.
Reference: Zu, Lei, et al. “A solution to the S8 tension through neutrino–dark matter interactions.” *Nature Astronomy* (2026): 1-9.
