20 February 2007
Space and particle physicists at the Swedish Institute of Space Physics, Uppsala University and Växjö University have shown that the Moon can be used as a giant detector for cosmic neutrinos of extremely high energies, a thousand-fold higher than what can be attained in particle physics accelerators. Such elementary particles carry information about extreme astrophysical and cosmological events, thus providing important information to help us understand physical processes that cannot be created in laboratories. These new results have just been published in the prestigious scientific journal Physical Review Letters on 16 February.
-- Success in observing such particles will open new windows both on the very largest, the universe, and the very smallest, the world of the elementary particles, which are its foundation, says Gunnar Ingelman, theoretical particle physicist at Uppsala University, and one of the authors of the article.
-- It is therefore of the utmost interest to find any conceivable way of studying these messengers from the universe which can reveal new, exciting physics, he continues.
The method proposed in the article is to pick up, on board a satellite orbiting the Moon, radio pulses which arise when the Moon is hit by neutrinos. Neutrinos have the unusual peculiarity that they pass through matter almost without a trace. This has the advantage that they can travel long distances through the universe without being affected or deviated and thereby provide information on their distant origin; the drawback is that very large detector volumes are required to measure them. Ultra-high-energy neutrinos are very rare and this makes the challenge even bigger. A new method relies on the fact that neutrinos sometimes give rise to particle showers which, when they interact with matter, "tear off" electrons that emit ordinary radio waves.
By analysing the lunar material brought back to Earth by the astronauts in the Apollo project, space researchers have been able to get a good idea about the physical properties of the Moon. Studies by the Swedish physicists have shown that these properties are suitable for the creation of radio emissions from cosmic neutrinos. However the radio emissions are so faint that one must either use huge radio telescopes on Earth, or the radio antenna must be close to the source, for instance on a satellite orbiting the Moon, where the radio interference from Earth is weak. The calculations presented show that by using advanced radio instrumentation from such a satellite it will be possible to pick up and analyse the radio emissions from the Moon. A Russian lunar satellite for this purpose is planned and will carry a unique Swedish radio instrument capable of measuring properties of radio emissions which no other existing instruments are capable of and which have been developed for the ground-based space radio infrastructure LOIS in Växjö in southern Sweden.
-- We find it exciting and stimulating that space and particle physics can cooperate in this way. The satellite technologies and new radio methods from space physics enable the particle physicists to make measurements that supplement those from large facilities on Earth. That this is of fundamental importance for our conception of the world pleases us even more, says Bo Thidé, professor of Space Physics at the Swedish Institute of Space Physics in Uppsala and visiting professor at Växjö University.
The article has its origin in results derived by Oscar Stål, at first as part of his diploma work at the Uppsala School of Engineering carried out in Bo Thidé's research group at the Swedish Institute of Space Physics in Uppsala, and later further developed as a graduate student in Gunnar Ingelman's research group at the Department of Nuclear and Particle Physics at Uppsala University.
-- This is very promising for the development of future cross-disciplinary collaborations which should strengthen and broaden Swedish space and particle physics, say Gunnar Ingelman and Bo Thidé.
For more information, please contact:
Oscar Stål, Jan Bergman, Bo Thidé, Lars Daldorff and Gunnar Ingelman, "Prospects for Lunar Satellite Detection of Radio Pulses from Ultrahigh Energy Neutrinos Interacting with the Moon", Physical Review Letters, Volume 98, Article number 071103, 16 February, 2007. http://link.aps.org/abstract/PRL/v98/e071103 http://arxiv.org/abs/astro-ph/0604199
The scientific journal Physical Review Letters is published by the American Physical Society.
The Swedish Institute of Space Physics (IRF) is a governmental research institute which conducts research and postgraduate education in atmospheric physics, space physics and space technology. Measurements are made in the atmosphere, ionosphere, magnetosphere and around other planets with the help of ground-based equipment (including radar), stratospheric balloons and satellites. IRF was established (as Kiruna Geophysical Observatory) in 1957 and its first satellite instrument was launched in 1968. The head office is in Kiruna (geographic coordinates 67.84° N, 20.41° E) and IRF also has offices in Umeå, Uppsala and Lund.
Institutet för rymdfysik, IRF, är ett statligt forskningsinstitut under Utbildningsdepartementet. IRF bedriver grundforskning och forskarutbildning i rymdfysik, atmosfärsfysik och rymdteknik. Mätningar görs i atmosfären, jonosfären, magnetosfären och runt andra planeter med hjälp av ballonger, markbaserad utrustning (bl a radar) och satelliter. För närvarande har IRF instrument ombord på satelliter i bana runt tre planeter, jorden, Mars och Saturnus. IRF har ca 100 anställda och bedriver verksamhet i Kiruna (huvudkontoret), Umeå, Uppsala och Lund.