LOFAR can now serve as a particle detector as well
An international team of astronomers has unravelled the radio signals that the LOFAR telescope in Drenthe receives if elementary particles from space collide with the earth's atmosphere. Thanks to that model the astronomers can now use LOFAR as a particle detector as well. The researchers published their findings on Thursday in Nature.
The astronomers, with a large number of Dutch researchers, studied 150 days of measurement data from so-called air showers. These particle cascades arise if cosmic elementary particles collide with the earth's atmosphere. The data reveal that the particles mainly consist of protons and the nuclei of helium atoms. Furthermore, it appears that most of the particles originate from our own Milky Way, and therefore not, as previously thought, from far away in the universe.
Stijn Buitink, professor at the Vrije Universiteit Brussel, is first author of the article. Buitink: "We think that a sort of particle accelerator is located in our galaxy and this is probably a very large star. This particle accelerator is millions of times stronger than the Large Hadron Collider (LHC) in Geneva."
Furthermore, based on the measurement data, the researchers could build a model that could accurately unravel the radio signals from the colliding cosmic particles. Such a model did not previously exist for radio signals.
Heino Falcke, astronomer at Radboud University: "We can now do very precise measurements and perform high-energy particle physics with the help of simple FM radio antennae like the ones we use at LOFAR. The particles come spontaneously out of space, free of charge. All we have to do is capture them."
The Dutch astronomers now want to use the technique elsewhere as well. Jörg Hörandel, astroparticle physicist at Radboud University, is currently involved in an international collaboration that is placing hundreds of radio antennae at the Pierre Auger Observatory in Argentina. Hörandel: "Pierre Auger is the largest experiment in the world for cosmic particles. With this new method we will ultimately be able to study cosmic particles with an even higher energy still and with unprecedented accuracy."
LOFAR was originally set up to study the cosmos. Now it can be used for particle physics as well. Previously the researchers used the radio signals from the air showers captured by LOFAR to study the electric field during thunderstorms.
The research was carried out with support from NWO, NOVA, SNN, the ERC and the FOM Foundation.
Reference
A large light-mass component of cosmic rays at 10^17–10^17.5 electronvolts from radio observations, S. Buitink et al, Nature, 3 March 2016. DOI: 10.1038/nature16976.