Tracing cosmic rays from radio pulses


The energy of ultra-high energy (UHE) cosmic rays that strike the Earth’s atmosphere make the energy produced from particle collisions by the Large Hadron Collider look puny. A team based in South Australia is now developing the techniques and technology to find out where such energetic particles could possibly originate. They ultimately hope to use the proposed SKA telescope to conduct their search.

“We think some cosmic rays are produced in the remnants of supernovae—exploding stars—but where the most energetic ones come from, that’s a mystery,” says Justin Bray, a PhD student hunting for their source as part of the LUNASKA (Lunar Ultra-high-energy Neutrino Astrophysics using SKA) project led by Ray Protheroe at the University of Adelaide and Ron Ekers at CSIRO.

The trouble is that cosmic rays are charged, so their trajectories are bent by magnetic fields, making it impossible to track their specific origin. However, theory predicts that whatever is producing the rays should also produce UHE neutrinos. “Neutrinos are uncharged and travel in straight lines, so if we are able to detect them then we might be able to detect the sources of cosmic rays,” says Ray.

Although UHE neutrinos can’t be detected directly, they should be detectable indirectly. As they strike the Moon, theory predicts that they should produce a particle cascade and a tell-tale radio pulse, as long as astronomers keep looking for long enough. The more sensitive the telescope, the more of these pulses should be detectable, and so the shorter the wait to catch one.

A CSIRO-led team is currently developing the necessary signal processing hardware using the dish at Parkes, Australia’s biggest current radio telescope. In addition, the team is developing technology needed to detect the pulses with the proposed SKA, the opening of which will mark the start of another phase of the UHE neutrino hunt. “If we don’t spot a neutrino with the dish at Parkes, we’ll have the technique worked out so that we can use the SKA when it’s ready,” says Justin.


School of Chemistry and Physics, University of Adelaide
Associate Professor Ray Protheroe, Tel: +61 (8) 8303 4748,,

CSIRO Astronomy and Space Science
Professor Ron Ekers, Tel: +61 (2) 9372 4600,