pulsars, which are like nature s clocks, really. 0n the dish of the giant lovell telescope, dr hannah middleton tells me that ideas on how galaxies merge and grow have all been theoretical until maybe now. we believe that galaxies and the black holes at the centre of them grow over time by mergers. but we haven t got evidence for this as yet. so if this is the signature of these mergers, it teaches us about the formation of galaxies throughout the universe. astronomers have made the detections by measuring the signals coming from spinning objects in space called pulsars, which are flashing stars at the end of their lives. pulsars are the lighthouses of the universe, sending out bursts of radio waves at regular intervals. the researchers noticed that something was changing their speed ever so slightly. they think that it s caused by gravitational waves constantly