An international team of astronomers have figured out radio signals that LOFAR captures when elementary particles from space collide with the Earth's atmosphere. Thanks to the model of the astronomers LOFAR is now able to act as a particle detector. The researchers published their findings last Thursday in Nature.

Published by the editorial team, 7 March 2016

The astronomers, with a group of Dutch at the base, studied 150 days of measurement data from so-called cosmic ray air showers. These air showers occur when cosmic, elementary particles collide with the Earth's atmosphere.

Data shows that the cosmic rays consist mainly of protons and nuclei of helium atoms. Furthermore, it seems that most of the particles come from our own Milky Way. And not, as was thought until now, from far out of the universe.



An artist's impression of cosmic ray air showers over the LOFAR superterp.
© Heino Falcke.

Stijn Buitink, professor at Vrije Universiteit Brussel, first author of the article. Buitink: We think there is some kind of particle accelerator in our own galaxy. Perhaps a very large star. This particle accelerator is a million times stronger than the Large Hadron Collider (LHC) in Geneva.

Furthermore, the researchers were able to create a model based on the data from the measurements. The model could unravel the radio signals from colliding cosmic particles accurate. Such a model didn’t exist for radio signals.

Heino Falcke, astronomer at Radboud University: We can now make very precise measurements and we are able to start high-energy particle physics using simple FM radio antennas as we use with LOFAR. The particles are free to pick up out of space. We just have to catch them.

The Dutch astronomers also want to apply the technique elsewhere. Jörg Hörandel, astroparticle physicist at Radboud University, is working on an international level to place hundreds of antennas 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 can eventually study cosmic rays of even higher energy and with unprecedented accuracy.

LOFAR was originally designed to study the universe. Now it can also be used for particle physics. Earlier, the researchers used the radio signals of the air showers caught by LOFAR to study the electric field during thunderstorms.

Article: A large light-mass component of cosmic rays at 10^17–10^17.5 electronvolts from radio observations. Door S. Buitink, et. al. Nature, 3 maart 2016. DOI: 10.1038/nature16976


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