Gravitational Wave Background
Over the last few years, gravitational wave detectors have become mainstream and routinely report mergers of black holes and neutron stars. But scientists are keen to go a stage deeper and try to measure a “gravitational wave background” analogous to the “Cosmic Microwave Background” that has informed so well on the origins of the cosmos. Rather than build evermore sensitive and expensive detectors, a rather clever idea has taken form. Scientists now monitor a number of Milky Way pulsars in all directions in the sky. Pulsars emit extremely regular pulsing signals as they rotate very fast, akin to accurate clocks. Now if the background gravitational waves are effectively pulling Earth a little in the direction of some pulsars and then away again, it ought to be possible to detect a very small corresponding change in the timing of these pulses. And moreover the lengthening of pulse timing in one direction should be matched by an equal shortening of pulses from pulsars in the opposite direction in the sky. The changes in timing are of the order of a few hundred nanoseconds. The collaboration (NANOGrav) have reported first evidence of these signals, though their analysis is at a very early stage.
