A neutrino telescope in the Antarctic ice
a transcript to accompany the Real Media
universe is full of mysteries. Only a part of its enigmatic
variety can be glimpsed with the human eye. Only by using
modern detection systems can scientists decode the invisible
messages from the cosmos.
some time there has been a new window into the universe that
permits us to see space under a totally different light: neutrino
astronomy. Physicists from the research center DESY, together
with American and European colleagues, operate the new neutrino
telescope. It consists of 670 light sensors, which are melted
into the ice of the South Pole. Its name: AMANDA!
AMANDA is an array of devices for detecting muons and neutrinos.
A constant rain of cosmic rays flows though the universe:
light, nuclei, neutrinos, and muons.
Neutrinos are extremely small elementary particles that have
one very particular feature: a strong antipathy for interaction
with other matter. Light and nuclei are often swallowed by
cosmic dust cloudsl neutrinos travel through space almost
Billions of neutrinos reach the earth every second. As messengers
from their place of origin, they carry information from very
distant galaxies, supernovae explosions, and undiscovered
Neutrinos are unaffected as they penetrate the Earth, and
as they travel through the glowing center of the planet.
Are they completely unaffected? Well, not quite.
A microscopic view shows how the travel of these ghost particles
can sometimes be stopped: by an extremely rare collision with
the nucleus of an atom.
Here is a neutrino colliding with a water molecule of the
arctic ice. This collision breaks the nucleus apart, and the
neutrino converts to a muon, which is basically a heavy electron.
From the side, you can see another view of the muon's birth.
This particular muon will be picked up by the detectors. Muons
are able to travel several kilometers through the ice. You
can recognize a muon that is traveling at nearly the speed
of light by a cone that follows it. This cone is similar to
a boat creating waves behind itself. Looking inside the light
cone, you can see its structure.
The muon emits almost undetectably weak, blue light rays outward
from its sides. Taken together, all these emitted rays form
a hollow cone behind the muon. In the darkness of the Antarctic
ice, this glow can be detected up to 100 m away. The AMANDA
detector, frozen in a depth of 1500 to 2000 m, is optimized
in order to see this light. AMANDA is built out of powerful
light sensors, which are packed into pressure-resistant glass
spheres. Several hundred of these, attached to steel cables,
have been placed more than a mile deep into the ice of the
South Pole, where they watch for these small cones of light.
When a muon flies through the AMANDA detector, each light
sensor registers the passing cone of light within one billionth
of a second. The sensors convert the light into electrical
signals, which travel to the surface of the Earth.
laboratory for AMANDA is at the South Pole, as is its computer
control center, which stores and processes the data. Scientists
at the center supervise the data recording and do the initial
analysis on it. Complex computer programs investigate the
chronological order and intensity of the signals. From this
information, scientists can calculate the most important information:
which direction the initial neutrino came from.
Several hundred neutrino reactions have been detected in trial
phases of the past years. In January, 2000, scientists and
engineers were able to finish the second phase of AMANDA's
expansion. There are now 670 light sensors in the ice, and
in a few years, a much larger telescope with 5000 light sensors
will be built.
What will the physicists discover? Huge energy-jets that generate
cosmic irradiation? The origin of the dark material? The birth
of a supernova? Or something totally different, something
not found in the catalog of their expections?
Nature almost always shows more imagination than the minds
of physicists. What surprises will the cosmos bring them through
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