Scientific American has more on how some astronomers are using the ocean itself to scan the skies:
Suspended near the bottom of the Mediterranean Sea off France and Italy, 126 football-sized glass spheres are already using the ocean itself as an instrument to search for signals from dark matter, supernovae and neutron star collisions. These are the first of many such globes deployed for a project called the Cubic Kilometer Neutrino Telescope, or KM3NeT.
KM3NeT is set to be installed throughout one cubic kilometer of water—enough for 400,000 Olympic swimming pools—split over two locations, turning the surrounding water into a giant lens. More than 6,000 spheres, each containing 31 highly sensitive detectors called photomultiplier tubes, will cling to strings anchored to the seafloor and kept taut by floats.
“Perhaps one or two neutrinos in a million will interact with quarks inside the nucleus of either hydrogen or oxygen” in the water, says the project’s physics and software manager, Paschal Coyle of the Marseille Particle Physics Center. “Because the cosmic neutrinos possess very high energy, the result of such interactions is the release of a charged particle that travels very fast.”
In fact, it travels through the water faster than light can, producing an effect Coyle likens to an optical equivalent of the Concorde jet’s sonic boom. Researchers can determine the original neutrinos’ energy and direction using the faint light released—so-called Cherenkov radiation—picked up by the undersea sensors.