archiv~1.txt: SETI [ASTRO] Detector In Polar Ice To Hunt For Neutrinos

SETI [ASTRO] Detector In Polar Ice To Hunt For Neutrinos

Larry Klaes ( )
Fri, 19 Mar 1999 09:03:14 -0500

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>Date: Fri, 19 Mar 1999 4:45:53 GMT
>From: Ron Baalke <>
>Subject: [ASTRO] Detector In Polar Ice To Hunt For Neutrinos
>Reply-To: Ron Baalke <>
>Office of News and Public Affairs
>University of Wisconsin-Madison
>Detector in polar ice to hunt for neutrinos
>The hunt for the cosmic neutrino is on.
>This winter, after an extensive shakedown period, the Antarctic Muon and
>Neutrino Detector Array or AMANDA, a novel telescope set kilometers deep
>in the ice at the South Pole, began its search for the ghost-like cosmic
>neutrino. The nearly massless particle is rocketed through space, scientists
>think, by supernovas, black holes, quasars, gamma ray bursts and whirling
>neutron stars.
>Unlike any other astronomical telescope ever built, AMANDA is not a telescope
>in the conventional sense. It is composed of 422 basketball-sized glass orbs,
>photomultiplier tubes arranged on cables and sunk deep into the Antarctic ice
>in concentric rings.
>The device looks down through the Earth and is designed to catch the fleeting
>signals left by cosmic neutrinos, high-energy particles that are believed to
>emanate from objects deep in space and whose bizarre properties permit them
>to pass through entire planets without skipping a beat.
>If AMANDA successfully detects cosmic neutrinos and traces their paths back
>to the objects from which they come, it will open a new window to the
>universe, permitting scientists to study some of the most intriguing
>phenomena in the cosmos, according to Francis Halzen, a UW-Madison scientist
>who helped develop the telescope.
>"We've spent over a year understanding the idiosyncratic nature of this
>instrument," says Halzen. "Nobody's ever built anything like this before."
>AMANDA was built with extensive support from the National Science Foundation
>and in collaboration with other institutions in Europe and the United States.
>The AMANDA telescope works by detecting the fleeting flashes of blue light
>created by muons, particles created when neutrinos occasionally collide with
>other subatomic particles called nucleons. The muon's flash of light creates
>a bow wave much like that made by a boat in water. In theory, the bow wave
>will point back to the source from which the neutrino comes.
>The deep Antarctic ice is crystal clear and, at great depths, is free of air
>bubbles and nearly free of other imperfections. It serves as an ideal medium
>in which to look for the rare signals left by the billions of neutrinos that
>continuously pass through the Earth.
>To detect these signals, AMANDA looks down through the Earth to suspected
>neutrino sources in the sky of the Northern Hemisphere.
>"If something emits a lot of gamma rays, it's a good bet there are a lot of
>neutrinos there," says Robert Morse, a UW-Madison physicist who has spent
>years helping oversee the construction of the AMANDA telescope.
>Suspected sources include black holes, the remains of supernovas, and neutron
>stars, planet-sized, burned out husks of stars that spin at amazing speeds.
>Other potential sources are what scientists call active galactic nuclei,
>things like quasars and blazers, extremely bright and energetic objects at
>the centers of distant galaxies.
>What all of these objects have in common, says Morse, is that they act like
>enormous versions of the accelerators scientists build on Earth to study
>high-energy, subatomic particles. They also are at great distances from
>"The sources are far away. Gamma ray bursts, for instance, could be three to
>five billion light years away, or maybe even half way to the suspected edge
>of the universe. So you need a big detector," Morse says.
>In conventional forms of astronomy, the photon, the particle that makes up
>visible light and other parts of the electromagnetic spectrum, is what
>is sampled by telescopes on remote mountaintops, satellites and radio
>telescopes. But photons can be deflected and absorbed as they traverse space
>and encounter interstellar dust and pockets of gas and radiation. The cosmic
>neutrino, on the other hand, is unhindered by such obstacles.
>The tradeoff, says Morse, is that neutrinos are very hard to detect.
>Moreover, the sun and cosmic rays crashing into the Earth's atmosphere
>also make neutrinos, creating a soup of high-energy particles. But neutrinos
>from different sources, whether the sun or from a distant black hole, have
>defining characteristics that would permit scientists to identify the
>particles of interest.
>"It's like a police line-up," says Morse. "They have to pass the test."
>Over the past year, the AMANDA telescope has been tuned and tested and has
>succeeded in sampling neutrinos, but not the cosmic neutrinos of interest.
>"We've gotten the apparatus tuned up to the point that what we're seeing
>really are neutrinos," Halzen says. "But the majority of the neutrinos we've
>seen are atmospheric neutrinos. What we have to do now is pick out that one
>event out of 10 million."
>Yet the neutrinos now being sampled by AMANDA are the highest energy
>neutrinos ever detected, according to Albrecht Karle, a UW-Madison physicist.
>And the muons they spawn are tracked in the AMANDA detector for distances of
>up to 400 meters through the crystal clear Antarctic ice.
>Constructed at a cost of $7 million over seven years, the AMANDA detector
>nearly double in size next year with the addition of seven more strings, each
>with 48 photomultiplier tubes. The ultimate configuration, says Morse, is a
>proposed cubic kilometer detector of 80 to 100 strings with as many as 5,000
>to 6,000 photomultiplier tubes.
>The larger telescope will not only make a bigger target for the elusive
>cosmic neutrino, but also will make a key diagnostic test, measuring the
>energy of neutrino particles more precisely. That enhancement would permit
>a search for neutrino oscillations on a cosmological scale, says Morse.
>"Neutrinos can bring us a message of the most violent and cataclysmic
>processes occurring at the very edge of the universe -- colliding black
>neutron stars and maybe even colliding galaxies," Morse says. "But it's very
>difficult to make the measurements. AMANDA, we think, is our best bet to do
>AMANDA: Facts at a glance
>What is AMANDA?
>AMANDA stands for Antarctic Muon and Neutrino Detector Array. A sort of
>telescope, it consists of strings of photomultiplier tubes sunk deep into
>the Antarctic ice using a hot-water drill. AMANDA is designed to detect the
>fleeting signatures of light left by cosmic neutrinos as they pass through
>the polar ice cap.
>What are neutrinos?
>Neutrinos are particles without electric charge and, as far as scientists
>know, they have no mass. Neutrinos are hard to find because their interaction
>with matter is extremely feeble, producing nothing more than a fleeting burst
>of light. Large, very sensitive detectors like AMANDA have the best chance
>to find the distant and exotic sources of cosmic neutrinos.
>Where do neutrinos come from?
>Scientists believe cosmic neutrinos are constantly bombarding the Earth from
>many distant sources, including:
>* Black holes: Massive black holes in the centers of galaxies swallow up most
>everything with huge gravitational pull.
>* Other galaxies: Supernovae, which are exploding stars, distant galaxies are
>believed to emit neutrinos.
>* Quasars: Quasars (quasi-stellar objects) have been enigmatic because they
>emit prodigious amounts of energy from a very compact source.
>Who cares?
>Scientists are searching for cosmic neutrinos because they promise insight
>into some of the most violent and enigmatic objects in the universe: black
>holes, supernovae and quasars. Finding the elusive particle would open a new
>realm of astronomy.
>Who pays?
>AMANDA is funded primarily by the National Science Foundation. UW-Madison
>and University of California-Irvine and UC-Berkeley have also made
>substantial contributions. Other partners in the AMANDA collaboration
>include Lawrence Berkeley National Laboratory, Stockholm University,
>University of Uppsala and DESY, the German national high-energy physics
>Frances Halzen, a UW-Madison scientist who helped develop AMANDA, shows the
>inside of one of the 422 basketball-sized glass orbs, called photomultiplier
>tubes, used to catch the fleeting signals left by high-energy neutrinos.