KM3NeT, a future European deep-sea research infrastructure, will host a neutrino telescope with a volume of several cubic kilometres at the bottom of the Mediterranean Sea that will open a new window on the Universe.
The telescope will search for neutrinos from distant astrophysical sources like gamma ray bursters, supernovae or colliding stars and will be a powerful tool in the search for dark matter in the Universe.
An array of thousands of optical sensors will detect the faint light in the deep sea from charged particles originating from collisions of the neutrinos and the Earth.
The facility will also house instrumentation from Earth and Sea sciences for long term and on-line monitoring of the deep sea environment and the sea bottom at depth of several kilometers.
A telescope beneath the sea
As you read this, strange sub-atomic particles called neutrinos are zapping straight through you. Many of these neutrinos
originate in the Earth’s atmosphere, but some come from further away, from deep within our galaxy or even the distant
reaches of the universe.
Because neutrinos have no electric charge and virtually no interaction with ordinary matter, they pass unhindered through
planets as well as people. This ability to cover vast distances without being deflected by matter or electromagnetic fields
makes neutrinos valuable to astronomers and astrophysicists.
Neutrinos can reveal objects such as gamma-ray bursts and supernovae too far away to be seen by ordinary telescopes or
cosmic-ray detectors. They can tell us about the invisible dust-shrouded core of our own galaxy, the Milky Way, and they
may help to pinpoint the elusive ‘dark matter’ that fills the universe. Unfortunately, the properties which make neutrinos
so useful to astronomers also make them practically impossible to detect. As a result, neutrino ‘telescopes’ are large,
complex and expensive.
The starting point for most neutrino detectors is a large volume of water or ice. On the rare occasions when a neutrino
does interact with a water molecule, it produces a faint flash of light that can be picked up by sensitive photodetectors.
Given enough water, a small fraction of the neutrinos passing through the detector – perhaps one in every 100 000 – will
trigger a measurable response.
The world already has several neutrino detectors hidden beneath oceans, lakes and Antarctic ice. KM3NeT is building
on these demonstration projects to create the blueprints for a practical neutrino telescope. Enclosing at least one cubic
kilometre of water, and with the potential to become even larger, the KM3NeT detector will sit at a depth of 2 500-5 000
metres in the dark, clear waters of the Mediterranean.
Thousands of photomultiplier tubes arranged in a three-dimensional grid will watch for the flashes of light – numbered
in tens or hundreds per year – that will reveal cosmic neutrinos. Although it is in the northern hemisphere, the telescope
will actually point south, towards the centre of the Milky Way, using the thickness of the Earth to screen out unwanted