Hundreds of thousands of unknown galaxies have been discovered in a major new international radio survey of the sky.

More than 200 astronomers from 18 countries have published their work on the survey in a special issue of the scientific journal Astronomy & Astrophysics, which features the first 26 research papers to be published based on the research.

The publications - based on only the first 2% of the sky survey - has revealed hundreds of thousands of galaxies which had never been detected before and provided data on the physics of black holes and how galaxy clusters evolve.

The galaxies were detected using the Low Frequency Array (LOFAR) telescope, which is located mainly in the Netherlands and it operated primarily by ASTRON, the Dutch astronomy institute.

Additional stations are based in Germany, the UK, France, Sweden, Poland and Ireland.


By using radio telescopes, the astronomers were able to "see" processes in the universe that aren't visible to optical instruments.

The papers that have been published cover astronomical topics as diverse as black holes, clusters of galaxies, and magnetic fields.

Dr Huub Rottgering of Leiden University in the Netherlands explained how it helped reveal where black holes - areas of spacetime so dense that even light can't escape - are located.

"If we take a radio telescope and we look up at the sky, we see mainly emission from the immediate environment of massive black holes," said Dr Rottgering.

"With LOFAR we hope to answer the fascinating question: 'Where do those black holes come from?' What we do know is that black holes are pretty messy eaters.

"When gas falls onto them they emit jets of material that can be seen at radio wavelengths," Dr Rpttgering added.

Image: The new radio survey has detected hundreds of thousands of new galaxies. Pic: ASTRON

The radio emissions have also pinpointed clusters of galaxies merging, which causes particles to accelerate.

Dr Amanda Wilber of the University of Hamburg explained: "With radio observations we can detect radiation from the tenuous medium that exists between galaxies.

"This radiation is generated by energetic shocks and turbulence. LOFAR allows us to detect many more of these sources and understand what is powering them," she added.

Dr Annalisa Bonafede, of the University of Bologna, added: "What we are beginning to see with LOFAR is that, in some cases, clusters of galaxies that are not merging can also show this emission, albeit at a very low level that was previously undetectable.

"This discovery tells us that, besides merger events, there are other phenomena that can trigger particle acceleration over huge scales," Dr Bonafede said.

Using low-frequency radio maps of the sky requires a lot of time both for the telescopes and for the computers collecting the data, and it requires large teams to analyse that data.

"LOFAR produces enormous amounts of data - we have to process the equivalent of ten million DVDs of data," said Dr Cyril Tasse of the Observatoire de Paris.

"The LOFAR surveys were recently made possible by a mathematical breakthrough in the way we understand interferometry", added Dr Tasse.

Moving on from the first 2% of the survey, the team aims to make sensitive and high-resolution images of the whole northern sky - although it isn't clear whether these will result in pictures as gripping as those collected in the Hubble Ultra Deep Field (HUDF) images.

They expect this will reveal 15 million radio sources in total.

"Just imagine some of the discoveries we may make along the way. I certainly look forward to it", said Carole Jackson, the director general of ASTRON.

"And among these there will be the first massive black holes that formed when the Universe was only a 'baby', with an age a few percent of its present age", added Dr Rottgering.