Gravity Tests with Pulsars Using New-Generation Radio Telescopes

Abstract

Pulsar timing is a powerful tool for studying a wide range of questions in fundamental physics, including the equation of state (EOS) of super-dense matter, tests of general relativity (GR) and alternative theories of gravity, and searching for a gravitational wave (GW) background at nanohertz regime. This dissertation investigates these problems using new-generation radio telescopes: the MeerKAT telescope, the Five-hundred-meter Aperture Spherical radio Telescope (FAST), and the future Square Kilometre Array (SKA). <br /> The first two studies focus on the still unique Double Pulsar system, PSR J0737-3039A/B. Being one of the most compact binary pulsar systems, a wealth of relativistic phenomena has been tested with unparalleled precision in the strong-field regime. With the superior sensitivity of new-generation radio telescopes, various higher-order contributions predicted by GR can be precisely tested, thereby allowing a measurement of pulsar A's moment of inertia (MOI). Such a measurement can be made via relativistic spin-orbit coupling, with the spin-down mass loss taken into account for the first time in the analysis. Based on the first MeerKAT observations of A, I simulate realistic data expected for MeerKAT and the SKA in the near future. The results suggest that an MOI measurement with 11% accuracy (68% confidence) is possible by 2030, which can provide complementary constraints on the EOS of nuclear matter. If by then the EOS is well constrained, it will allow a 7% test of Lense-Thirring precession or a 3s-measurement of the next-to-leading-order (NLO) GW damping. <br /> With 3-yr MeerKAT observations of PSR J0737-3039A, I then study gravitational signal propagation effects in the Double Pulsar system, in particular the NLO effects predicted by GR. These include the retardation effect caused by the movement of pulsar B while the radio signal of A propagates across the system and the deflection of the signal of A by the gravitational field of B. The result provides an independent confirmation of the NLO signal propagation effects and is 1.65 times better than the previous measurement from 16-yr data. Novel effects like lensing and profile variations caused by latitudinal deflection are also investigated but proved to be not measurable with the current data. <br /> Recently, a new timing model has been developed for testing scalar-tensor gravity with binary pulsars. As a demonstration of this model, I explore the prospects of testing Damour–Esposito-Farèse (DEF) gravity by simulating realistic future data of the pulsar-white dwarf system PSR J2222-0137 and hypothetical pulsar-black hole systems for a number of large telescopes, including FAST. The results indicate that future observations can significantly improve the constraints on DEF gravity, and pulsar-black hole systems have the potential to place the tightest limit for a large part of the DEF gravity parameter space. <br /> Finally, to facilitate the detection of nanohertz GWs with pulsar timing arrays, I extend and correct the time offset measurements between the maser clock at the Effelsberg telescope and UTC. This rescues more than two years of timing data with Effelsberg and improves the accuracy of the time tagging of observations, which are critical for pulsar timing. In addition, phased-array observations have been carried out with Effelsberg and FAST, which can dramatically increase the sensitivity of telescopes and advance GW detection. By coherently adding data from the largest radio telescopes in Europe and China, the world's largest and most powerful pulsar telescope will finally materialise.