Is Darkish Matter Sterile? | by Brian Koberlein



9 July 2015

A comparison of a cold dark matter galaxy with a sterile neutrino galaxy. Credit: M Lovell/ICC Durham
A comparability of a chilly darkish matter galaxy with a sterile neutrino galaxy. Credit score: M Lovell/ICC Durham

Is darkish matter sterile? That’s one concept just lately offered on the Nationwide Astronomy Assembly of the Royal Astronomical Society this week.

Darkish matter is the enigmatic materials that appears to dominate our universe. From its gravitational results it appears to be about 5 instances extra widespread than the common matter that makes up stars, planets, you and me. However because it doesn’t work together with mild it has been troublesome to watch instantly. This has led some to suggest modified gravity fashions to get rid of the necessity for darkish matter, however this strategy has been unsuccessful to date. One other strategy is to suggest some new form of matter that might be darkish matter, resembling WIMPs or axions. However what if darkish matter is a brand new number of a recognized particle. That is the place sterile neutrinos come into the sport.

A neutrinos are a product of radioactive decay, and solely work together with matter by the weak drive. There are three recognized kinds of neutrinos, however due to their small mass and excessive speeds they can not clarify the results of darkish matter. However neutrinos have the weird property that when they’re produced they all the time spin in the identical course relative to their movement. This spin-motion connection is named helicity, and basically might be proper handed or left handed. If you happen to think about your thumb pointing within the course of a particle’s movement, along with your curled fingers representing the course of the spin, then you possibly can see which is which. Neutrinos are all the time shaped with a left handed helicity.

Sterile neutrinos would have a right-handed helicity. Due to this they wouldn’t work together with common matter (therefore sterile). Relying on the mannequin, they might theoretically have a lot larger lots than common neutrinos, which might clarify darkish matter. Within the latest presentation at NAM2015, a group checked out pc simulations of conventional chilly darkish matter fashions and sterile neutrino fashions. What they discovered is that sterile neutrinos appeared to be a barely higher match to noticed galaxies.

Whereas that is attention-grabbing, the sterile neutrino mannequin is just not with out its issues. For instance, there may be cosmological proof that factors to the universe solely having three neutrino varieties. Additionally, chilly darkish matter fashions stay one of the best match on giant cosmic scales.

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