Pulsar Astrophysics at Jodrell Bank: Rolling Grant 2009-2014

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Radio pulsars are very compact, rotating, massive and dense stars, consisting mainly of neutrons, that emit a radio beam along their magnetic axis. They are what remains when a star about eight times heavier than our Sun runs out of fuel and undergoes a catastrophic collapse that results in a supernova. The immense pressure during that collapse squashes matter slightly heavier than our Sun into a sphere of just 10 kilometre in radius, converting the matter into neutrons. As the pulsar rotates, the narrow radio beam sweeps across the Earth and we detect a pulse of radiation, much like a cosmic version of a lighthouse, and hence the name pulsar. The extreme density, equivalent to fitting the entire Earth into a golf-ball, means that pulsars rotate very stably. Each pulse is like a tick from a clock which has an accuracy which rivals that of the best atomic clocks on Earth. We can use this clock-like nature of pulsars to perform incredible experiments on gravity which are only possible with pulsars. For example, if a pulsar is in a binary system with another star, then Einstein's theory of General Relativity predicts that the time that it will take the two stars to orbit each other will decrease with time due to the emission of gravitational waves. The predicted decrease in the orbital period was first measured by Hulse & Taylor using pulsars, for which they were awarded the Noble Prize in Physics in 1993. This was strong proof that Einstein's theory was correct but this was only indirect evidence for the existence of gravitational waves, a direct detection has not yet been made. Representing objects with the largest matter density in the observable Universe, pulsars also have extremely large magnetic fields, about 30 million times that of the strongest magnetic we can produce on Earth. It is in these magnetic fields that the radio emission is generated which is seen as the accurate pulses. How this process works tests the limits of our physical understanding and allows us to measure the properties of matter and plasma in environments which are impossible to recreate in a laboratory. In order to be able to perform all of these exciting studies, we first have to find sufficient numbers, and the right sort, of pulsars on which to do these experiments. Our group is the world's most successful one in finding radio pulsars but even more extreme objects are still to be found. In order to find these missing jewels, we are planning to use some of the largest telescopes in the world, together with a very large computer and sophisticated software that we have developed. We expect to find about 1000 new pulsars! We also continue to use the currently best known objects to test Einstein's theory of gravity. This includes timing the unique Double Pulsar, which we discovered in 2003. In this object, two pulsars orbit each other in less than 2.5 hours, moving with speeds of 1 million km/h. Using it, we have tested Einstein to be correct at least the 99.95% level. To directly detect gravitational waves for the first time, we are planning a unique experiment to measure the arrival time of pulses from pulsars with the highest precision yet achieved. This requires us to record and combine the signals of the 5 largest telescopes in Europe to form an enormous dish equivalent to the largest in the world. An important factor in our research is the possibility to use the Lovell telescope. As one of the greatest pulsar telescopes in the world, we track the rotation of more than 600 pulsars, leading to many unexpected and exciting results about neutron star properties, dense matter and even the events during the collapse of a massive star. All of our proposed experiments require cutting edge bespoke technology much of which we develop ourselves. This state-of-the art software and hardware proposed in this grant allows us to perform these incredibly precise measurements of these extreme objects.