The Biggest Underwater Telescope At a depth of 3500 meters
Tolone is a city in southeastern France with about 170.000 inhabitants.
It is located on the Mediterranean coast, on the bay of the Grande Rada.
It is the first city on the Côte d'Azur starting from the west.
Portopalo di Capo Passero is a very small Italian town of about 4000 inhabitants, located
in Sicily.
It is sadly famous for the so-called Christmas '96 massacre, a tragic event that devastated
the country on 25 and 26 December 1996.
The sinking of a ship carrying migrants claimed 283 victims, and it represented the largest
naval tragedy in the Mediterranean since the end of the second world war.
Pylos, instead, is a Greek town in Greece.
Of 55000 inhabitants, according to the 2001 census data.
It is historically known for having been the scene of two naval battles: the battle of
Pylos ( 425 BC ), during the Peloponnesian War, and the battle of Navarino ( 1827 ), an
episode of the Greek war of independence.
But why are we talking about these cities?
Even if they seem to have nothing in common, something is going on between them, something
that links them.
And it has something to do with astrophysics, neutrinos and telescopes.
Follow me in this video to get to know more
about it: you will be amazed.
The initial idea of neutrino astronomy beyond the solar system rested on two arguments.
First.
Astronomers thought that a supernova collapse in our galaxy, the Milky Way, would be accompanied
by bursts of highly energetic neutrinos.
Second.
Pulsars, accelerating particles thanks to their enormous magnetic fields, must accelerate
particles and generate neutrinos as decay products of some mother-particles, called
pions.
In the fifties and sixties, astronomers were struggling to find a good way to detect such
neutrinos.
The first ideas to detect cosmic high energy neutrinos date back to those years.
Brilliant minds suggest constructing a large Cherenkov counter, where the Cherenkov light
is the light that extra-terrestrial particles release when they penetrate into the Earth's
atmosphere.
More precisely, Cherenkov radiation is the light produced when a particle travels through
a medium faster than light.
Nothing travels faster than light in a vacuum, but the light is slowed down when travels
through a medium like water, for instance, while other particles are not.
The result is the eerie blue glow produced in nuclear reactors, which is analogous to
a sonic boom but for light: Just like a fighter jet produces sound waves that travel slower
than the jet itself, the particle produces light waves that travel slower than the particle
itself.
This Cherenkov counter would be about 15 meters in diameter, located in a mine far underground.
This was an unusual choice: what's the purpose of an underground telescope?
How can we detect signals from the sky if we put them in a mine?
Anyway, they also told that the counter should be surrounded with photomultipliers to detect
the events, and enclosed in a shell of scintillating material to distinguish neutrino events from
those caused by other particles.
Such a detector would be very expensive.
So...was the juice worth the squeeze?
It depended on the estimated number of neutrinos they were expecting to detect by means of
such a telescope.
During the sixties, no acceptable theory of the origin and extraterrestrial diffusion
existed, so that the cosmic neutrino flux could not be usefully predicted.
But things changed when, in the late sixties and early seventies, many objects were discovered.
For example, the first quasar in 1963, pulsars in 1967 and X-ray binaries with a black hole,
in 1972.
These objects were identified as possible neutrino emitters, giving an enormous push
to theoretical physics activity.
Soon after, scientists understood the importance of building such telescopes, and the importance
of neutrinos in terms of cosmology, physics and astrophysical processes.
That's why, as today, underground and underwater telescopes are not so unusual, and they are
giving us precious scientific results.
But why do we need to place such telescopes underwater, or underground?
Neutrinos are tiny particles.
They are so tiny, that their interaction rate with the matter in the universe is really
low.
Because they only weakly interact with other particles, neutrino detectors must be very
large to detect a significant number of them.
Yet neutrinos are omnipresent in nature.
Every second, tens of billions of them pass through every square centimetre of our bodies,
and you can't even notice that!
We are literally bombarded with neutrinos.
Many of them were created right after the big bang but, according to theory, we think
some of them originate from magnificent events in the universe, such as colliding black holes
event or gamma-ray bursts from exploding stars, or violent events at the cores of distant
galaxies.
Due to their low interaction with matter, and due to their low mass and lack of electric
charge, neutrinos are extremely difficult to detect.
Many neutrino detectors are located deep underground in order to minimize the interference of cosmic
rays on the detectors.
While it might seem empty, space is a noisy place; an infinity of different signals are
constantly bouncing around, and reducing this noise is one of the main challenges of a neutrino
detector.
Some famous neutrino detectors are Super Kamiokande, buried at 3,300 feet underground beneath Mount
Ikeno, near the City of Hida, in Japan.
Another one is the IceCube detector, located in the South Pole beneath the Antarctic Ice.
With ongoing activities about neutrinos and the first ideas on a telescope in polar ice,
the exploration of the Mediterranean sea as a site for an underwater neutrino telescope
was quite natural.
And this is what the three cities mentioned before have in common.
They are located in the Mediterranean region.
At about 80 km to the coast of Capo Passero, in Sicily, and at a depth of 3500 metres beneath
the sea, scientists and engineers are building the biggest underwater telescope ever built.
Sailed from Malta on board the Miss Marilene Tide ship, the revelator's components were
surrounded with a shell and put into the Sicilian sea.
This brand new telescope is called Cubic Kilometer Neutrino Telescope, or KM3NeT.
It is a future European scientific research infrastructure.
It will contain a new generation neutrino telescope in the form of a Cherenkov detector,
with a volume of five cubic kilometres distributed in three positions in the Mediterranean: KM3Net-Fr
in off Toulon, France KM3NeT-It in Italy, Capo Passero, and KM3NeT-Gr off Pylos, Greece.
As you can see, science has the ability to link cities that apparently don't have anything
in common!
This is what we mean when we say that science is an instrument of peace among countries
and people.
This amazing telescope will search for neutrinos from supernova remnants, gamma-ray bursts
or extragalactic object collisions.
It will be a powerful tool because it could also help in the search for dark matter in
our universe.
Its sensors will aim to detect light in deep water from charged particles originating from
neutrino collisions with water or rocks near the detector.
The entire infrastructure will also contain instrumentation for other scientific branches
such as marine biology and geophysics.
The final structure will consist of seven large sub-detectors, six of which will be
used for astrophysical purposes.
This telescope will be really one of a kind!
It will contain about 12.000 pressure-resistant glass spheres attached to 600 strings, and
each rope will hold 18 spherical sensors, supported by floats.
Each sphere has a diameter of 43 cm and contains photomultiplier tubes, connected to the coast
by a broadband fibre-optic network.
As we can read on the KM3NeT website:
“KM3NeT is a research infrastructure housing the next generation neutrino telescopes.
Once completed, the telescopes will have detector volumes between megaton and several cubic
kilometres of clear seawater.
Located in the deepest seas of the Mediterranean, KM3NeT will open a new window on our Universe,
but also contribute to the research of the properties of the elusive neutrino particles.
With the ARCA telescope, KM3NeT scientists will search for neutrinos from distant astrophysical
sources such as supernovae, gamma-ray bursters or colliding stars.
The ORCA telescope is the instrument for KM3NeT scientists studying neutrino properties exploiting
neutrinos generated in the Earth's atmosphere.
Arrays 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 for Earth and Sea sciences for long-term and
online monitoring of the deep-sea environment and the sea bottom at depth of several kilometres.
“
Okay, so now we know a lot of things about KM3NeT, but we have one question left: why
study neutrinos?
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Neutrinos are by far the most abundant particles in the universe.
The combination of that ghostly presence and the important role neutrinos play in the universe
captivates physicists.
Neutrinos play a role in many fundamental aspects of our lives; they are produced in
nuclear fusion processes that power the sun and stars, they are produced in radioactive
decays that provide a source of heat inside our planet, and they are produced in nuclear
reactors.Â Neutrinos are believed to be a vital ingredient in a star’s supernova process.
These explosions spread heavy elements throughout space, elements that are needed to create
the universe we live in.
Neutrinos also provide a tool to study the structure of nucleons (protons and neutrinos),
to learn how matter evolved from simple particles into more complex composites of particles,
creating everything around us.
Talking about cosmology, for example, neutrinos could play a big role in the asymmetry of
matter events that happened in the early universe.
Let me explain.
The big bang produced an equal amount of matter and antimatter.
This means, for example, that for each electron, in the beginning, we think there was an anti-electron,
called a positron.
But today's observations are clearly showing that we live in a universe dominated by matter.
Where did all of the antimatter go?
Scientists think there was a tiny asymmetry that allowed the matter to dominate antimatter.
Were neutrinos involved in this asymmetry?
It could be.
We have just to wait and see what we will discover next.
Meanwhile...remember to keep it curious!
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