Potential of radio telescopes as high-frequency gravitational wave detectors

TL;DR

This paper explores how radio telescopes can detect high-frequency gravitational waves through their interaction with cosmic magnetic fields, leading to observable distortions in the cosmic microwave background, and provides new bounds on gravitational wave amplitudes.

Contribution

It demonstrates a novel method of using radio telescope measurements to set bounds on high-frequency gravitational waves via photon-gravitational wave conversion in magnetic fields.

Findings

Radio telescopes can constrain gravitational wave amplitudes at MHz to GHz frequencies.

Current bounds surpass laboratory constraints by about seven orders of magnitude.

Future 21cm astronomy could improve sensitivity to gravitational waves.

Abstract

In the presence of magnetic fields, gravitational waves are converted into photons and vice versa. We demonstrate that this conversion leads to a distortion of the cosmic microwave background (CMB), which can serve as a detector for MHz to GHz gravitational wave sources active before reionization. The measurements of the radio telescope EDGES can be cast as a bound on the gravitational wave amplitude, $h_c < 10^{-21} (10^{-12})$ at 78 MHz, for the strongest (weakest) cosmic magnetic fields allowed by current astrophysical and cosmological constraints. Similarly, the results of ARCADE 2 imply $h_c < 10^{-24} (10^{-14})$ at $3 - 30$ GHz. For the strongest magnetic fields, these constraints exceed current laboratory constraints by about seven orders of magnitude. Future advances in 21cm astronomy may conceivably push these bounds below the sensitivity of cosmological constraints on the total energy density of gravitational waves.