A New Class of Radio Halo

Galaxy clusters are the largest gravitationally bound systems in the Universe and their interactions via collisions and mergers are the most energetic events since the Big Bang. The gas in these systems is mixed with magnetic fields and relativistic particles, creating diffuse, megaparsec-scale synchrotron radiation at the cluster center which can be observed at radio wavelengths. Currently detected in only a fraction of known interacting clusters, this emission is called a radio halo. A team of scientists, including astronomers from the Naval Research Laboratory, has detected a radio halo at long wavelengths in a colliding, massive galaxy cluster surprisingly, it is not detected at the shorter wavelengths where these objects are typically seen. The discovery implies that existing radio telescopes have missed a large population of these colliding objects in fact it suggests a new class of radio halos. These halos could be uniquely studied at long radio wavelengths, using new, more sensitive telescopes currently being built, such as the NRL-conceived Long Wavelength Array LWA.