The European astronomers took images of 'Whirlpool Galaxy' Messier 51 (M51) with the Low Frequency Array (LOFAR) radio telescope in the frequency range 115-175 MHz that is just above the normal commercial FM radio frequency band of 88-108 MHz.

Radio astronomy has not been able to explore low frequencies below 300 MHz because the ionosphere around the Earth acts as a barrier of low-frequency radio waves. The only observations were of poor resolution and no details could be made out.

‘Low-frequency radio waves are important as they carry information about electrons of relatively low energies that are able to propagate further away from their places of origin in the star-forming spiral arms and are able to illuminate the magnetic fields in the outer parts of galaxies,’ said David Mulcahy from the University of Southampton's astronomy group.

The signals from all stations of LOFAR spreading across the Netherlands, Germany, Britain, France and Sweden were combined in a powerful computing cluster located at University of Groningen in the Netherlands.

With LOFAR's high sensitivity, the astronomers detected electrons and magnetic fields in the spiral arms and extended disc of M51, 40,000 light years away from the galaxy's centre - much further out than had ever been traced before.

Radio astronomy shows two crucial components of galaxies that are invisible to optical telescopes - cosmic ray electrons and magnetic fields - which play an important role in the stability and evolution of galaxies.

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