StrongField Gravity Tests with the Double Pulsar
Abstract
Continued timing observations of the double pulsar PSR J07373039A/B, which consists of two active radio pulsars (A and B) that orbit each other with a period of 2.45 h in a mildly eccentric (e =0.088 ) binary system, have led to large improvements in the measurement of relativistic effects in this system. With a 16yr data span, the results enable precision tests of theories of gravity for strongly selfgravitating bodies and also reveal new relativistic effects that have been expected but are now observed for the first time. These include effects of light propagation in strong gravitational fields which are currently not testable by any other method. In particular, we observe the effects of retardation and aberrational light bending that allow determination of the spin direction of the pulsar. In total, we detect seven postKeplerian parameters in this system, more than for any other known binary pulsar. For some of these effects, the measurement precision is now so high that for the first time we have to take higherorder contributions into account. These include the contribution of the A pulsar's effective mass loss (due to spindown) to the observed orbital period decay, a relativistic deformation of the orbit, and the effects of the equation of state of superdense matter on the observed postKeplerian parameters via relativistic spinorbit coupling. We discuss the implications of our findings, including those for the moment of inertia of neutron stars, and present the currently most precise test of general relativity's quadrupolar description of gravitational waves, validating the prediction of general relativity at a level of 1.3 ×10^{4} with 95% confidence. We demonstrate the utility of the double pulsar for tests of alternative theories of gravity by focusing on two specific examples and also discuss some implications of the observations for studies of the interstellar medium and models for the formation of the double pulsar system. Finally, we provide context to other types of related experiments and prospects for the future.
 Publication:

Physical Review X
 Pub Date:
 October 2021
 DOI:
 10.1103/PhysRevX.11.041050
 arXiv:
 arXiv:2112.06795
 Bibcode:
 2021PhRvX..11d1050K
 Keywords:

 Astrophysics  High Energy Astrophysical Phenomena;
 General Relativity and Quantum Cosmology
 EPrint:
 56 pages, 23 Figures. Published by Physical Review X. Uploaded ArXiv version is authors' (preproof) version with abbreviated abstract. Resubmission for updated acknowledgement information. For final published version see https://link.aps.org/doi/10.1103/PhysRevX.11.041050