The Double Pulsar: A Rare Laboratory for Relativistic Gravity and Pulsar Emission Physics

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Neutron stars are the compact, highly magnetized remnants of massive stars that have ended their lives in supernova explosions. These stars weigh more than the Sun and yet are only 10 miles across, making them the densest objects next to black holes. Some of these neutron stars are seen as radio pulsars, which emit beams of radio emission detectable by telescopes on Earth as they spin. The rotation periods of pulsars are incredibly stable, allowing them to be used as ultra-precise cosmic clocks for fundamental physics experiments. Roughly 300 of the 2500 known pulsars are in binary systems with other stars, and only 10 of these are in binary systems with other neutron stars. The large masses and short orbital periods of these double neutron star binaries make them remarkable laboratories for fundamental physics, and in particular for testing Einstein's theory of general relativity. One of these double neutron star binaries is truly exceptional, as it is the only one in which both of the neutron stars are detectable as radio pulsars. This makes the tests of general relativity more precise than for any other system and provides the best test ever of general relativity in the so-called strong-field regime. We also observe interactions between the two pulsars which can be used to help understand pulsar emission physics. This proposal will fund analysis of high-precision data taken with the Green Bank Telescope in Green Bank, WV, that will provide even better tests of general relativity and provide crucial information about the emission mechanisms and geometries of the two pulsars in the system. The information gleaned from the observations of this system is truly unique and the goals could not be achieved through any other means.While the investigators are focused on one system, the implications of the work are vast. The techniques they develop will be crucial for future double pulsar systems sure to be discovered through upcoming wide-field pulsar surveys. They will also develop an animation which will be of interest to the general public, students, and scientists. This animation will show how the pulse profile of B varies with time due to geodetic precession and the changing influence of pulsar A. These animations will be hosted on a website which will include other educational materials on the Double Pulsar, pulsar properties, general relativity, and gravitational wavesGeneral relativity (GR) is the most elegant and complete description of gravity ever produced. The investigators will make more sensitive GR tests, including the elimination of alternative theories of gravity and, possibly, the measurement of second-order Post-Keplerian corrections to lead to the first measurement of a NS moment of inertia. This would provide a unique constraint on the NS equation of state. This work will also lead to measurement of fundamental properties of the system that will inform understanding of binary evolution, pulsar emission physics, and detection rates for ground-based interferometers that cannot be measured in any other way. It will also provide crucial input for gravitational wave detectors, facilitating one of the most important scientific milestones of the decade.