# Limits on the anomalous speed of gravitational waves from binary pulsars

## TL;DR

This paper constrains the speed of gravitational waves using binary pulsar data, showing it can only differ from light speed by a very small percentage, thus limiting certain dark energy models.

## Contribution

It derives a generalized gravitational wave emission formula for arbitrary propagation speeds and applies it to pulsar data to set bounds on deviations from light speed.

## Key findings

- Gravitational wave speed differs from light speed by less than a few percent.
- Tight constraints on dark energy models with anomalous gravitational wave speeds.
- Revised period decay formula accounting for variable gravitational wave speeds.

## Abstract

A large class of modified theories of gravity used as models for dark energy predict a propagation speed for gravitational waves which can differ from the speed of light. This difference of propagations speeds for photons and gravitons has an impact in the emission of gravitational waves by binary systems. Thus, we revisit the usual quadrupolar emission of binary system for an arbitrary propagation speed of gravitational waves and obtain the corresponding period decay formula. We then use timing data from the Hulse-Taylor binary pulsar and obtain that the speed of gravitational waves can only differ from the speed of light at the percentage level. This bound places tight constraints on dark energy models featuring an anomalous propagations speed for the gravitational waves.