Binary-pulsar tests of strong-field gravity

TL;DR

Binary pulsar observations provide crucial tests for strong-field gravity theories, revealing deviations from general relativity in regimes inaccessible to solar-system experiments.

Contribution

This work reviews four key binary-pulsar experiments and demonstrates their ability to constrain tensor-scalar gravity theories, including models indistinguishable from GR in weak fields.

Findings

Binary pulsar data exclude some scalar-tensor theories.

Strong-field tests differ qualitatively from solar-system tests.

Binary pulsars are essential for probing gravity near compact objects.

Abstract

This talk is based on my work in collaboration with Thibault Damour since 1991. Unified theories, like superstrings, predict the existence of scalar partners to the graviton. Such theories of gravity can be very close to general relativity in weak-field conditions (solar-system experiments), but can deviate significantly from it in the strong-field regime (near compact bodies, like neutron stars). Binary pulsars are thus the best tools available for testing these theories. This talk presents the four main binary-pulsar experiments, and discusses the constraints they impose on a generic class of tensor-scalar theories. It is shown notably that they rule out some models which are strictly indistinguishable from general relativity in the solar system. This illustrates the qualitative difference between binary-pulsar and solar-system tests of relativistic gravity.