 Comparison of density distribution in the Universe with (left) and without (right) massive neutrinos. The maps are based on numerical simulations. The colors account for the density of ordinary (baryonic) matter in one slice of the simulation box. The two simulations started from the same initial conditions, with either M?=0 (right) or M?=1.9 eV (left). In the massive neutrino case, matter is spread over a larger number of structures and there is less density contrast. (The unrealistically large neutrino mass of 1.9 eV was chosen so as to make the comparison clear.) Illustration: Courtesy of Shankar Agarwal and Hume Feldman, University of Kansas; submitted to Mon. Not. R. Astron. Soc. |
It seems that neutrinos are at best half as massive as previously estimated, according to an analysis appearing in the journal Physical Review Letters.
The lower neutrino mass estimate is the result of a 3-dimensional survey of more than 700,000 galaxies called MegaZ DR7.
Although neutrinos are very light and interact with matter very rarely, they are so numerous that they can have a significant effect on the evolution of the material distribution in the universe.
The galactic distributions revealed in the MegaZ map appear consistent with a reduced upper limit of neutrino mass estimates.
There are restrictions on the information the map can provide, in part because there are three varieties of neutrinos (electron, muon, and tau neutrinos), each of which likely have different masses.
As a result, MegaZ can only estimate the sum of the three neutrino masses. The galactic distribution suggests that the combined mass the three neutrino varieties is less than 0.28 electron volts.
Although the survey doesn't offer a lower limit of neutrino masses, it's clear from the detection of neutrinos coming from our sun, as well as from laboratory experiments, that neutrinos have at least some mass.
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