Detecting Exoplanets beyond the Local Supercluster through Gravitational Waves with B-DECIGO and DECIGO

The first detection of a gravitational-wave (GW) signal in 2015 has opened a new observational window to probe the Universe. This probe can not only reveal previously inaccessible binaries, black holes, and other compact objects, but also can detect exoplanets through their imprint on GW signals, thereby significantly extending current exoplanet surveys. To date, nearly 6000 exoplanets have been confirmed, yet most of them reside either in the solar neighbourhood or along the sightline toward the Galactic bulge, reflecting the range limits of traditional electromagnetic techniques. In this work, we adopt the method proposed in N. Tamanini & C. Danielski to investigate frequency modulations in GW signals from early-stage binary neutron stars induced by circumbinary planets (CBPs) and find that CBPs can be detected by the future space-borne detector Deci-hertz Interferometer Gravitational-wave Observatory (DECIGO). For a binary neutron star system with the masses of two components, both being 1.4 M ⊙ , DECIGO could detect CBPs with masses dozens of times that of Jupiter out to distances of ∼1 Gpc, well beyond the Local Supercluster, offering an unprecedented opportunity to study planetary formation and evolution for the post-main-sequence stage.