Pointing the Very Large Array (VLA) radio telescope in New Mexico at a famous galaxy for the first time in two decades, a team of astronomers from the Astrophysics Research Institute at Liverpool John Moores University and the National Radio Astronomy Observatory got a big surprise, finding that a bright new object had appeared near the galaxy's core.
The object, the scientists concluded, is either a very rare type of supernova explosion or, more likely, an outburst from a second supermassive black hole closely orbiting the galaxy's primary, central supermassive black hole.
All large galaxies are thought to have a large black hole - typically a million times more massive than our Sun - at their centre, and for a small subset of those galaxies the black hole is active, accelerating fast jets of relativistic matter out into intergalactic space. What makes some of these black holes active, and other black holes (such as the one at the centre of our own Milky Way galaxy) inactive, is unknown.
Astronomers have long suspected the collisions between galaxies play a key role - a hypothesis supported by the discovery of this new source of radio emission in one of the most powerful active galaxies in the Universe.