Galaxies galore

A TEAM of more than 200 astronomers from 18 countries, including India (Pune University), has published the first phase of a major new radio sky survey using the Low Frequency Array (LOFAR) radio telescope, which is in The Netherlands. The survey has revealed hundreds of thousands of previously undetected galaxies, shedding new light on many research areas. A special issue of the journal “Astronomy & Astrophysics” published the first 26 papers describing the survey and its first results.

Radio astronomy reveals processes in the universe that cannot be seen with optical telescopes. In this first part of the sky survey, LOFAR mapped 300,000 sources, almost all of which are galaxies in the distant universe whose radio signals travelled billions of light years before reaching the earth. Black holes are messy eaters and when gas falls onto them they emit jets of material that can be seen at radio wavelengths. “We hope to answer the fascinating question, where do those black holes come from?” said Huub Rottgering of Leiden University. “LOFAR has a remarkable sensitivity and that allows us to see that these jets are present in all of the most massive galaxies, which means that their black holes never stop eating,” added Philip Best of the University of Edinburgh. A radio emission from clusters of galaxies, which are ensembles of hundreds to thousands of galaxies, occurs when two clusters merge. This emission comes from particles that are accelerated during the merger. “This radiation is generated by energetic shocks and turbulence. LOFAR allows us to… understand what is powering them,” Amanda Wilber of Hamburg University said. “What we are beginning to see with LOFAR is that, in some cases, clusters... that are not merging can also show this emission... [which] tells us that there are other phenomena that can trigger particle acceleration over huge scales,” said Annalisa Bonafede of Bologna University. “ ...the unprecedented accuracy of the LOFAR measurements has allowed us to measure the effect of cosmic magnetic fields on radio waves from a giant radio galaxy that is 11 million light years in size.... LOFAR [will] help us understand the origin of cosmic magnetic fields,” pointed out Shane O’Sullivan of Hamburg University.