Credit: NASA
SYDNEY: Astronomers have found a new way to search for high-energy cosmic rays, the most energetic particles in the universe, by scanning the face of the Moon.
Cosmic rays stream through space and constantly bombard the Earth's atmosphere. They pose little threat to us on the planet's surface, but can cause electronic glitches in satellites in space and, in high doses, are dangerous for astronauts.
Ultra-high-energy cosmic rays, with energies exceeding 1020 electron volts, were first detected in 1962.
Black holes
Their origin has not been proven, although theories suggest they may be created by the supermassive black holes thought to be at the heart of galaxies or result from the decay of massive particles leftover from the Big Bang.
A variety of large, Earth-bound experiments have been constructed to detect these cosmic rays.
In 2007 one statistical study, based on data from the Pierre Auger observatory in Argentina, showed that some of the highest energy cosmic rays detected seem to come from the direction of known active galactic nuclei (see Black holes: source of high-energy cosmic rays, Cosmos Online).
Now, Australian and Spanish researchers say they have found a bigger and better target for detecting the rays - the regolith (dusty rock) of the Moon. The research was presented at the 31st International Cosmic Ray Conference, held in Poland last month, and is also is posted on the arXiv.org physics web site.
Useful target
The team, led by astrophysicists Ray Protheroe from the University of Adelaide and Ron Ekers of the CSIRO's Australia Telescope National Facility, looked for high-energy neutrinos – particles with little mass, which are similar to electrons, but neutrally charged.
"Whenever cosmic rays are accelerated to these tremendous energies in space you'll also get neutrinos of comparable energies produced," Protheroe told Cosmos Online. "Not being charged they travel in a straight line through space, and are not deflected by magnetic fields."
This makes neutrinos a useful target for pinpointing the origin of cosmic rays, he said. But because they interact only weakly with other matter and are very rare, you need a huge target and sensitive instruments to detect them.
