Neutrinos are popular right now. 

Last week the IceCube neutrino observatory announced the discovery of the origin of many high energy cosmic rays as being a massive black hole and active galaxy, using the flux of neutrinos that it produced as a pointer to their source. The observations were then confirmed by a variety of observatories working in radio waves, visible light, and gamma-rays, but the original signal was through neutrinos.

Today we have the announcement that the University of Victoria, where I did my own graduate work, is installing a neutrino detector and observatory of its own.

Although neutrinos are plentiful, there nature makes them very difficult to detect. Neutrinos do not interact with electromagnetic fields, and as such they pass through matter unimpeded. They cannot be focused or reflected, and they cannot be captured by any form of sensor. However there is a very small probability that a given neutrino will hit an atomic nucleus, and convert a proton into a neutron or a neutron into a proton (depending on whether it is a neutrino or an antineutrino impacting the nucleus). This reaction also produces either electrons or positrons (or their heavier counterparts, the muon and the tau lepton), and the interactions of these charged particles with surrounding matter subsequently results in a small number of photons being generated. 

Due to the very small rate of neutrino interactions, experiments that are studying neutrinos need to be very large. In the case of the IceCube experiment, the "detector" is actually a cubic kilometer of ice under the South Pole. Scientists have filled the ice with photomultiplier tubes that can reproduce the photons they receive and amplify the signal to a measurable level. By analyzing the distribution and energy spectrum of the photons, physicists can determine when a neutrino has interacted with the ice. It was this method that allowed scientists to trace the origin of high energy cosmic rays to a distant black hole at the center of an active galaxy.

Now scientists locally are building their own version of a neutrino detector and observatory. Instead of using a massive block of ice, a series of detectors will be placed at the bottom of the ocean and will be able to detect interactions of cosmic neutrinos with the large volume of water above the detectors. Since the detectors are actually searching for bursts of light coming from the charged particles produced by neutrino impacts, it is important that they are placed in very dark locations - which makes the bottom of the ocean a perfect option. 

This new experiment will be part of the existing network of oceanography experiments that have been installed in the Pacific ocean over the past twenty years, and are monitored by scientists at the University of Victoria and elsewhere. The neutrino observatory will also be connected to similar experiments elsewhere in the world, so that any interesting neutrino bursts can be measured at multiple locations by multiple experiments. 

At this point we do not know what this new experiment might find, but last week's announcements by the IceCube observatory make neutrino astronomy much more plausible and interesting. And more experiments collecting more data is always a good thing for science!