Testing the Motion of Strongly Self-Gravitating Bodies with Radio Pulsars
Before the 1970s, precision tests for gravity theories were constrained to the weak-field environment of the Solar System. In terms of relativistic equations of motion, the Solar System gave access to the first order corrections to Newtonian dynamics. Tes
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Abstract Before the 1970s, precision tests for gravity theories were constrained to the weak-field environment of the Solar System. In terms of relativistic equations of motion, the Solar System gave access to the first order corrections to Newtonian dynamics. Testing anything beyond the first post-Newtonian contributions was for a long time out of reach. The discovery of the first binary pulsar by Russell Hulse and Joseph Taylor in the summer of 1974 initiated a completely new field for testing the relativistic dynamics of gravitationally interacting bodies. For the first time the back reaction of gravitational wave emission on the binary motion could be studied. Furthermore, the Hulse-Taylor pulsar provided the first test bed for the orbital dynamics of strongly self-gravitating bodies. To date, there are a number of binary pulsars known which can be utilized to test different aspects of relativistic dynamics. So far GR has passed these tests with flying colors, while many alternative theories, like scalar-tensor gravity, are tightly constraint by now. This article gives an introduction to gravity tests with pulsars, and summarizes some of the most important results. Furthermore, it gives a brief outlook into the future of this exciting field of experimental gravity.
1 Introduction In about two years from now we will be celebrating the centenary of Einstein’s general theory of relativity. On November 25th 1915 Einstein presented his field equations of gravitation (without cosmological term) to the Prussian Academy of Science [1]. With this publication, general relativity (GR) was finally completed as a logically consistent physical theory (“Damit ist endlich die allgemeine Relativitätstheorie als logisches Gebäude abgeschlossen.”). Already one week before, based on the vacuum form of his field equations, Einstein was able to show that his theory of gravitation naturally explains the anomalous perihelion advance of the planet N. Wex (B) Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: [email protected] URL: http://www.mpifr-bonn.mpg.de/staff/nwex/ © Springer International Publishing Switzerland 2015 D. Puetzfeld et al. (eds.), Equations of Motion in Relativistic Gravity, Fundamental Theories of Physics 179, DOI 10.1007/978-3-319-18335-0_20
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Mercury [2]. While in hindsight this can be seen as the first experimental test for GR, back in 1915 astronomers were still searching for a Newtonian explanation [3]. In his 1916 comprehensive summary of GR [4], Einstein proposed three experimental tests: • Gravitational redshift. • Light deflection. • Perihelion precession of planetary orbits. Gravitational redshift, a consequence of the equivalence principle, is common to all metric theories of gravity, and therefore in some respect its measurement has less discriminating power than the other two tests [5]. The first verification of gravitational light bending during the total eclipse on May 29th 1919 was far from being a high precision test, but clearly decided in
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