A New International Telescope Is Being Built At The Bottom Of The Sea

Artist's impression of KM3NeT. This is the view from inside a detector building block of detection units. Copyright Edward Berbee/Nikhef

Scientists are building a huge next-generation telescope in a very peculiar location: the bottom of the Mediterranean Sea. They are not planning to look at the light of distant stars or galaxies. There in the darkness, deep underwater, they hope to catch the signals of some special cosmic particles.

The telescope is going to study neutrinos, the tiny neutral particles that can travel through anything without interacting. In fact, trillions of neutrinos passed through your body as you read this sentence. Given that they hardly interact, scientists have had to build increasingly clever detectors. The Cubic Kilometre Neutrino Telescope, or KM3NeT, is one.

“Neutrinos very rarely interact, however when a neutrino hits the water it generates light, which the KM3NeT telescope is able to detect,” Dr Clancy James from the Curtin Institute of Radio Astronomy and the International Centre for Radio Astronomy Research (ICRAR) in Australia, said in a statement.

“The underwater telescope is bombarded by millions of different particles but only neutrinos can pass through the Earth to reach the detector from below so, unlike normal telescopes, it looks down through the Earth at the same sky viewed by upward-facing telescopes in Australia.” Curtin University has just joined the collaboration. 

KM3NeT is currently being built in two locations with a potential extension for a third one pending funding. One is off the coast of the French Riviera and will mainly study “local” neutrinos. The other is off the coast of Sicily and will look at the high-energy neutrinos that come from supernovae explosions, neutron star mergers, and many other astrophysical phenomena.

“This project will help us answer some of the major questions around particle physics and the nature of our universe, potentially ushering in a new era in neutrino astronomy,” Dr James continued.

The first construction phase for the telescope involves placing 30 detection units on the seabed, each of them a line with 18 detectors. In the darkness of the deep sea, these instruments can record the flashes of light produced by neutrinos interacting with seawater. Despite still being under construction, both locations have detection units that are already in place and collecting data. The team expects 115 detection units to be deployed in the final phase of construction.

KM3NeT is not the only neutrino telescope in the world. Similar in approach but different in design is IceCube in Antarctica, which uses the frozen ice of the South Pole instead of the seawater of the Med to spot neutrinos. Networked together, the two will be able to detect neutrino events anywhere in the sky.

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