3 December 2020
It’s usually stated that we haven’t but detected darkish matter particles. That isn’t fairly true. We haven’t detected the particles that comprise chilly darkish matter, however we’ve got detected neutrinos. Neutrinos have mass and don’t work together strongly with mild, so they’re a type of darkish matter. Whereas they don’t clear up the thriller of darkish matter, they do play a job within the form and evolution of our universe.
From the proof we’ve got of darkish matter, such because the clustering of galaxies and gravitational lensing, we all know that the majority darkish matter should be chilly. Which means it’s probably fabricated from heavy particles. A spread of potentialities has been proposed, from unique particles known as axions to tiny primordial black holes. Up to now, no such answer has been discovered. However whereas most darkish matter should be chilly, different darkish matter that’s heat or scorching may additionally play a job.
Neutrinos are a type of scorching darkish matter. The temperature of a fabric is set by the velocity of its particles. Since neutrinos transfer at almost the velocity of sunshine, they’re a type of scorching matter. For a very long time it was thought that neutrinos had been massless, and thus wouldn’t be part of darkish matter. Then within the Nineteen Nineties, they had been discovered to have a tiny quantity of mass. Their mass is so small that we don’t know what it’s. We solely know that neutrinos have mass as a result of the state of a neutrino can change over time via a course of referred to as oscillation. This wouldn’t be attainable in the event that they had been massless and moved on the velocity of sunshine.
So neutrinos are part of darkish matter, however what position do they play? That’s the query lately explored within the Astrophysical Journal. The group ran pc simulations on how neutrinos work together on a cosmic scale. Since they don’t know the mass of neutrinos, they created a simulation the place they may fluctuate the mass to review completely different outcomes. They discovered that whereas neutrinos do are likely to clump with galaxies, they really work to hinder the quantity of clustering by chilly darkish matter. The quantity of hindrance is determined by the mass of the neutrinos.
Earlier research have proven how neutrino mass may have an effect on cosmic evolution, however this research exhibits how neutrinos can have an effect on chilly darkish matter. Additional analysis may even enable astronomers to make use of galactic clustering to pin down the mass of neutrinos, thus utilizing essentially the most large objects within the universe to measure particles with the tiniest mass. It’s a scorching concept that might be fairly cool.