Detecting Gravitational Waves with an International Pulsar Timing Array

Einstein's  general relativity is a theory of gravity and gravity is a rather weak force, usually requiring massive astronomical bodies to test the theory and its predictions. One of these predictions revolves around the essential concept that space and time are combined to form “space-time” which is curved in the presence of mass. As masses move, for instance like the two components in a binary system, ripples in space-time are created that propagate through the Universe, very much like waves caused by a stone falling into a pond. These “gravitational waves” are known to exist from the effect that they have on a system of two orbiting stars where the orbit shrinks because the GWs carry away energy, however they have never been detected directly.  One way to do this is to use some the best clocks in the Universe, radio pulsars. These enigmatic objects weighabout 1.5 times the mass of our Sun and yet are the size of a city, they have magnetic field strengths a billion times more than those of the Earth and they rotate up to 716 times a second.  As they rotate, beams of radio emission emitted from their magnetic poles sweep across the Earth and are detected by the largest radio telescopes in the world.  The extreme density of these objects combined with their rapid rotation rates means that these pulses of radio emission arrive very regularly which is what makes them such excellent clocks. Monitoring the times of arrival of the pulses from about two dozen pulsars allows us to build a Galaxy-sized detector for gravitational waves. Using radio pulsars we are sensitive to gravitational waves from very early in the history of the Universe, most likely from merging supermassive blackholes. I will explain the way in which we can use this instrument to directly detect gravitational waves. I will discuss the three different experiments being performed around the world, centered on the largest radio telescopes in the world, and also the International Pulsar Timing Array which will combine the data from all three experiments to make the most sensitive measurements ever. Finally I will consider the prospects for the study of gravitational waves with the next generation radio telescope, the Square Kilometer Array.