We give a brief description on the scientific principles behind the
AMANDA concept. This page is intended to assist the media and the general
public understand the goals and operation of the AMANDA detector.
You can also get the latest scientific
results from AMANDA.
All telescopes, whether they are radio telescopes, microwave telescopes, infrared telescopes, x-ray telescopes, gamma-ray telescopes, and of course optical telescopes like the 10m Keck Telescope in Hawaii collect electromagnetic waves (or "light"). AMANDA breaks from this honorable tradition. It is designed to detect high energy NEUTRINOS, a ghostly particle with little mass and even less inclination to socialize. The latter property makes it almost ideal as a particle messenger. Once produced, the travel path of a neutrino will be unaffected by galactic magnetic fields, intergalactic material such as dust , or cosmic microwave background light. In fact, virtually nothing can prevent a neutrino from traveling to the AMANDA detector at the South Pole. This is quite a contrast with electromagnetic waves such a light. At high enough energies, the universe is opaque to light! For example, a particle of light with energies in excess of 100 TeV cannot reach us from even the nearest galaxies outside the Milky Way.
Neutrinos carray information from the central engines of spectacularly
powerful objects in space. For example, enormous black holes are
thought to power the output of active galactic nuclei (AGN), but precise
knowledge of the physics mechanisms remain elusive. One concept is shown
next. A supermassive black hole is surrounded by a donut of material
which feeds the powerful jets of accelerated particles (yellow cones).
The neutrino cannot be detected directly by AMANDA (nor any other detector for that matter). Rather we rely on a surrogate particle called a "muon".
The next figure shows the process in a bit more detail. The Cherekov light is emitted at about 45 degrees to the direction of travel. By measuring the time that the Cherenkov light arrives at each sensor (called an optical module, or OM), we can deduce the direction of the muon. The the graphic below, the middle OM of the rightmost string will see light first, then the bottom OM, and so on. The OMs in AMANDA measure the time that the photon strikes the OM with great precision.
Hi Resolution of AMANDA OM
|A few more bits of information are required to fully understand the
design. First, a neutrino is not the only particle that can create
a muon. In fact, it is downright easy for ordinary cosmic rays to make
muons when they collide with the atmosphere of the earth. The muons
from cosmic ray collisions are are more common than muons from neutrinos,
so how do we tell the difference? We use the trick of looking through
the center of the earth (in other words, AMANDA looks down instead of up
like ordinary telescopes!). Neutrinos are the only particles we know
that can penetrate the earth. In astronomy terms, our "dark sky" is beneath
AMANDA. Anyway, neutrinos are the only particle capable of producing
a muon with a direction that comes from below the horizon of the detector.
So if the direction of the particle is upward, we know it was produced
by a neutrino that interacted within a few miles of the detector.
The blizzard of muons from cosmic ray collisions with the atmosphere can be reduced in intensity by going underground. That is one of the reasons why AMANDA is buried so deep (the other reason? Antarctic ice only becomes transparent to Cherenkov light at depths greater than 1400 meters).
The architecture of AMANDA was selected because of its simplicity and reliability. In fact, the technologies used in the AMANDA string, optical modules, and surface electronics were chosen for their robustness against harsh environmental conditions. The basic physics principles that guide the design of AMANDA are not so different from those employed by many detectors in high energy astrophysics, as the schematic shows
If you wish to learn more on how the AMANDA detector was constructed
at the geographic south pole and a walking tour of the Amundsen-Scott South
Pole station, then go here.
Physicists on AMANDA worked closely with the Polar Ice Coring Office (PICO)
to develop the machinery to drill holes in the ice to the necessary depths
and diameter. They had to brave bone-chilling conditions to
drill the holes and deploy the strings of sensors.
Full waveform captured by prototype DAQ. The source of light was an in situ nitrogen laser. The red vertical lines indicate the photon arrival times collected by the standard AMANDA DAQ. Notice that the waveforms contain far more information.
Electronics used to capture waveforms. This picture was taken at the South Pole.