Today’s factismal: In 1988, Takaaki Kajita and Arthur McDonald discovered that the Sun wasn’t going to explode.
If you look at the Sun (which you shouldn’t do because it can cause serious damage to your eyes), then odds are you’ll see it as a bright, burning spot in the ten seconds or so that you have before you do serious damage to your eyes (told you so). But when an astronomer looks at the Sun through a telescope with a strong filter that makes it safe to do so, she sees something different. The astronomer sees both the source of all our power and an amazing set of atomic reactions known as the solar phoenix. In this reaction, six protons combine to form a helium nucleus, two spare protons, two gamma rays, and two anti-electrons (aka positrons). But there is something else created in that reaction; something that is so small and slippery that it is almost impossible to catch: the neutrino.
The solar phoenix reaction. The little νs are neutrinos being given off in the first stage.
The neutrino is special because without it, the solar phoenix reaction simply can’t happen. Even though it is so small that it would take a million of them to have the same mass as a single electron, the neutrino is essential to the solar phoenix and many other nuclear reactions. It is created in nuclear reactors as a byproduct of fission; roughly 4.5% of the energy in a nuclear reactor is lost as neutrinos!
And the neutrino can also be created by particle accelerators. When they smash two tiny protons or electrons together, they make even smaller bits, one of which is the neutrino. Neutrinos are made in so many ways that they are the second most common particle in the Universe (after the photon), and may be responsible for the “missing mass” known popularly as Dark Matter.
Neutrinos are very, very, very, very, very, very, very, very, very, very, very, very, very, very small
The neutrino is special in another way, too. It is the only particle that has been the cause of five Nobel Prizes. The first went to Enrico Fermi in 1938, who predicted its existence in 1933 based on a “missing” amount of energy in what physics wonks call slow neutron reactions (this also led to the discovery of the weak force); amusingly, Fermi’s paper was rejected by the leading scientific journal of the day as being “too remote from reality”. The second was given in 1995 to Clyde Cowan, Frederick Reines, F. B. Harrison, H. W. Kruse, and A. D. McGuire who discovered the neutrino in 1956 (take THAT, leading scientific journal). The third went to Leon M. Lederman, Melvin Schwartz and Jack Steinberger in 1988 for their discovery in 1962 that there was more than one type of neutrino; physicists refer to the three types as flavors because whimsy. The fourth Nobel Prize for neutrino-related work was given in 2002 to Raymond Davis, Jr. and Masatoshi Koshiba for their detection of neutrinos from a supernova; today, the field they founded is known as neutrino astronomy. And the fifth prize (thus far) was awarded in 2015 to Takaaki Kajita and Arthur McDonald who proved that neutrinos change flavors as they move.
The Sun generates energy by making big atoms out of little ones (Image courtesy NASA)
That is important because until 1988, there was serious concern that the Sun might be going out; about half of the astrophysicists thought it would be with a whimper and the other half thought it would be with a bang. That was because we weren’t detecting the right number of neutrinos from the Sun. Even though the neutrino is so small and interacts too weakly with other matter that it is almost impossible to catch, the Sun puts out so many neutrinos (roughly 1.3 x 1018 each second, or 185 million for every person on Earth) that we can still see some of them. Only we weren’t seeing enough of them. Though we knew that neutrinos had different flavors, the Standard Model in physics said that the neutrinos should stay the same flavor; discovering that they changed flavors would mean that the Standard Model was wrong.
The Sudbury Neutrino Observation detector being installed
(Image courtesy CoolCosmos)
And in 1988, using neutrinos captured from reactions in the atmosphere and neutrinos from the Sun’s core, two teams led by Takaaki Kajita and Arthur McDonald discovered that neutrinos do indeed change flavor. The Standard Model was wrong (and the Sun was saved). Thanks to their work, we are learning more about how these small but vital particles help the Universe go round. And last year, they were awarded the Nobel Prize for their work.
If you’d like to learn more about particle physics and maybe do a little prize-worthy work of your own, why not head over to LHC@Home? This website, offered by the same folks who invented the internet, has several different ways to get involved in the search more new and even more interesting particles. To learn more, zip on over to: