Will Gravitational Waves Discover the First Extra-Galactic Planetary System?

TL;DR

This paper explores the potential of space-based gravitational wave detectors to discover the first extragalactic planetary systems, expanding the scope of exoplanet detection beyond our galaxy.

Contribution

It proposes that gravitational wave observations can detect extragalactic circumbinary planets, a novel application beyond previous Galactic-focused studies.

Findings

Gravitational waves can reveal massive circumbinary exoplanets.

Detection of extragalactic planetary systems is theoretically possible.

Space-based GW detectors could identify planets in satellite galaxies.

Abstract

Gravitational waves have opened a new observational window through which some of the most exotic objects in the Universe, as well as some of the secrets of gravitation itself, can now be revealed. Among all these new discoveries, we recently demonstrated [N. Tamanini & C. Danielski, Nat. Astron., 3(9), 858 (2019)] that space-based gravitational wave observations will have the potential to detect a new population of massive circumbinary exoplanets everywhere inside our Galaxy. In this essay we argue that these circumbinary planetary systems can also be detected outside the Milky Way, in particular within its satellite galaxies. Space-based gravitational wave observations might thus constitute the mean to detect the first extra-galactic planetary system, a target beyond the reach of standard electromagnetic searches.