Absorption of gravitational waves from distant sources

Raphael Flauger,Steven Weinberg

doi:10.1103/physrevd.99.123030

Abstract

The rate of gravitational wave absorption by inverse bremsstrahlung is calculated. It increases with decreasing frequency $\nu$ as $\nu^{-3}$. Nevertheless, because of the near cancellation of absorption by stimulated emission, the ionized gas in galaxy clusters does not block gravitational waves at the nanohertz frequencies that may be detected by the use of pulsar timing observations.

Highlights

The exciting discovery of gravitational waves from coalescing black holes [1] and neutron stars [2] has naturally increased interest [3] in possible effects that intervening matter may have on these waves
There is an old result of Hawking [4], that gives the rate of absorption as Γabs 1⁄4 16πGη=c2, where η is the viscosity of the matter, but this only applies if the collision frequency in the matter is much greater than the frequency of the gravitational wave, which it typically is not
We have recently studied the opposite extreme case of gravitational wave propagation through collisionless matter [5], but we found no observable effects, except perhaps for cosmological sources

Summary

Raphael Flauger*

Theory Group, Department of Physics, University of Texas Austin, Texas 78712, USA (Received 31 May 2019; published 28 June 2019). The rate of gravitational wave absorption by inverse bremsstrahlung is calculated. It increases with decreasing frequency ν as ν−3. Because of the near cancellation of absorption by stimulated emission, the ionized gas in galaxy clusters does not block gravitational waves at the nanohertz frequencies that may be detected by the use of pulsar timing observations

INTRODUCTION

RAPHAEL FLAUGER and STEVEN WEINBERG