Mass of Neutrinos Accurately Calculated for First Time, Physicists Report

Physicists report they are now able to better understand the age and shape of the universe after accurately measuring the mass of neutrinos for the first time.

Neutrinos are ghostly subatomic particles that, by all reasoning, should have a minute mass, but until now that mass has never been accurately calculated, which has posed problems with what's known as the standard model of cosmology. Neutrinos are difficult to study because they interact so weakly with matter.

A better understanding of the physical properties of neutrinos is of scientific interest because the information could be used to study environments currently unobservable with light or radio waves.

Writing in the journal Physical Review Letters, scientists from the universities of Manchester and Nottingham report that they deduced the mass of neutrinos by using data from the European Space Agency's Planck space observatory and additional measurements of gravitational lensing, the phenomenon of light from distant galaxies being magnified as it passes through closer galaxies.

By examining the oldest light in the universe, fading glow of the Big Bang known as cosmic microwave background (CMB), the researchers pinpointed some inconsistencies in the standing theories on neutrinos and their place in the universe.

"We observe fewer galaxy clusters than we would expect from the Planck results and there is a weaker signal from gravitational lensing of galaxies than the CMB would suggest," said Richard Battye, from The University of Manchester School of Physics and Astronomy.

"A possible way of resolving this discrepancy is for neutrinos to have mass. The effect of these massive neutrinos would be to suppress the growth of dense structures that lead to the formation of clusters of galaxies," he said.

Among physicists, the types of neutrinos are knows as different "flavors." While originally thought to be massless, these various neutrinos flavors have recently been estimated to have a total mass of 0.06 electron volts (eV), which is far less than a billionth of the mass of a proton.

However, this calculation faces an inconsistency when large-scale structures of the universe, such as the distribution of galaxies, are observed, the researchers said. But these inconsistencies can be resolved for if the mass of neutrinos is included in the standard cosmological model, the researchers report, suggesting that the sum of the masses of three known neutrino flavors is 0.320 +/- 0.081 eV.

"If this result is borne out by further analysis, it not only adds significantly to our understanding of the sub-atomic world studied by particle physicists, but it would also be an important extension to the standard model of cosmology which has been developed over the last decade," said Adam Moss, from the University of Nottingham.