The Moon Helps Radio Astronomers Search for Neutrinos

by Nancy Atkinson on November 30, 2010

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Radio astronomers get an assist from the Moon. Credit: Ted Jaeger, University of Iowa, NRAO/AUI/NSF

From an NRAO press release:

Seeking to detect mysterious, ultra-high-energy neutrinos from distant regions of space, a team of astronomers used the Moon as part of an innovative telescope system for the search. Their work gave new insight on the possible origin of the elusive subatomic particles and points the way to opening a new view of the Universe in the future.

The team used special-purpose electronic equipment brought to the National Science Foundation’s Very Large Array (VLA) radio telescope, and took advantage of new, more-sensitive radio receivers installed as part of the Expanded VLA (EVLA) project. Prior to their observations, they tested their system by flying a small, specialized transmitter over the VLA in a helium balloon.

In 200 hours of observations, Ted Jaeger of the University of Iowa and the Naval Research Laboratory, and Robert Mutel and Kenneth Gayley of the University of Iowa did not detect any of the ultra-high-energy neutrinos they sought. This lack of detection placed a new limit on the amount of such particles arriving from space, and cast doubt on some theoretical models for how those neutrinos are produced.

Neutrinos are fast-moving subatomic particles with no electrical charge that readily pass unimpeded through ordinary matter. Though plentiful in the Universe, they are notoriously difficult to detect. Experiments to detect neutrinos from the Sun and supernova explosions have used large volumes of material such as water or chlorine to capture the rare interactions of the particles with ordinary matter.

The ultra-high-energy neutrinos the astronomers sought are postulated to be produced by the energetic, black-hole-powered cores of distant galaxies; massive stellar explosions; annihilation of dark matter; cosmic-ray particles interacting with photons of the Cosmic Microwave Background; tears in the fabric of space-time; and collisions of the ultra-high-energy neutrinos with lower-energy neutrinos left over from the Big Bang.

Radio telescopes can’t detect neutrinos, but the scientists pointed sets of VLA antennas around the edge of the Moon in hopes of seeing brief bursts of radio waves emitted when the neutrinos they sought passed through the Moon and interacted with lunar material. Such interactions, they calculated, should send the radio bursts toward Earth. This technique was first used in 1995 and has been used several times since then, with no detections recorded. The latest VLA observations have been the most sensitive yet done.

“Our observations have set a new upper limit — the lowest yet — for the amount of the type of neutrinos we sought,” Mutel said. “This limit eliminates some models that proposed bursts of these neutrinos coming from the halo of the Milky Way Galaxy,” he added. To test other models, the scientists said, will require observations with more sensitivity.

“Some of the techniques we developed for these observations can be adapted to the next generation of radio telescopes and assist in more-sensitive searches later,” Mutel said. “When we develop the ability to detect these particles, we will open a new window for observing the Universe and advancing our understanding of basic astrophysics,” he said.

The scientists reported their work in the December edition of the journal Astroparticle Physics.

Source: NRAO

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Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

Lawrence B. Crowell November 30, 2010 at 6:02 PM

There is a rub with the idea. Neutrinos can pass through lots of material. However, the few which do interact with material in the moon will produce secondary particles which are likely produced deep in the lunar material and absorbed. The neutrino must interact with material pretty close to the surface in order to produce particles we could detect. Further, these neutrinos are very unlikely to produce photons with very large wavelength. However a muon detector buried deep in the surface might catch an event how and then.

LC

mick December 1, 2010 at 1:21 AM

As far as I understood the article, mentionned interactions are supposed to leave radios footprints. Which I think do travel through material pretty well.

M

Uncle Fred December 1, 2010 at 1:26 AM

What exactly is Nancy referring to when she mentioned “tears i the fabric of space-time?” Is this a reference to the dark flow?

Lawrence B. Crowell December 1, 2010 at 5:41 AM

“Tears in the fabric of spacetime” is a euphemism for domain walls or cosmic strings and other plausible physical structures. It is worth working on how we could maybe observe neutrinos from the earliest period of the universe. The breaking of the symmetry of the universe at very high energy split the QCD field from the weak interactions and on the family level lepton and quark doublets from each other. These should have been a burst of neutrinos produced then. These neutrinos should be highly red shifted (yes they are wave fields and red shifted like light), there should be some interesting issues with CP symmetry and that they have come from beyond the cosmological event horizon. CP symmetry violation means these neutrinos have their angular momentum or spin oriented opposite to their momentum. However, if you boost your frame to that of the neutrino (since neutrinos have a small mass) there is no momentum vector, and if you boost your frame to an even higher velocity you can then observe the spin oriented along the observed momentum of the neutrino. Neutrinos produced at the earliest moments of the universe are nearly at rest on the current Hubble frame. There then should be some physics with how neutrinos become Majorana, where the anti-neutrino and neutrino states become equivalent.

LC

Torbjorn Larsson OM December 3, 2010 at 7:36 AM

a reference to the dark flow?

tThere doesn’t seem to be such a thing.

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