Pulsars and Gravity

TL;DR

Pulsars serve as precise natural laboratories for testing relativistic gravity and detecting gravitational waves, with recent results strongly supporting Einstein's theory and constraining alternative models.

Contribution

This paper reviews how pulsars, especially millisecond pulsars, are used to test relativistic gravitation and explore gravitational wave detection through Pulsar Timing Arrays.

Findings

Pulsar timing confirms Einstein's general relativity in strong-field regimes.

PTAs set new limits on nanohertz gravitational wave background.

Observations constrain models of galaxy and black-hole evolution.

Abstract

Pulsars are wonderful gravitational probes. Their tiny size and stellar mass give their rotation periods a stablility comparable to that of atomic frequency standards. This is especially true of the rapidly rotating "millisecond pulsars" (MSPs). Many of these rapidly rotating pulsars are in orbit with another star, allowing pulsar timing to probe relativistic perturbations to the orbital motion. Pulsars have provided the most stringent tests of theories of relativistic gravitation, especially in the strong-field regime, and have shown that Einstein's general theory of relativity is an accurate description of the observed motions. Many other gravitational theories are effectively ruled out or at least severely constrained by these results. MSPs can also be used to form a "Pulsar Timing Array" (PTA). PTAs are Galactic-scale interferometers that have the potential to directly detect nanohertz gravitational waves from astrophysical sources. Orbiting super-massive black holes in the cores of distant galaxies are the sources most likely to be detectable. Although no evidence for gravitational waves has yet been found in PTA data sets, the latest limits are seriously constraining current ideas on galaxy and black-hole evolution in the early Universe.