• Article
    | Open Access

    Pulsar timing arrays enable the search for the isotropic gravitational-wave (GW) background originating from super massive black hole binary populations, but impose a stringent upper limit on the GW characteristic amplitude. Here, the authors use Bayesian hierarchical modelling applied to a range of astrophysical scenarios to revisit the implications of this upper limit.

    • Hannah Middleton
    • , Siyuan Chen
    •  & Alberto Vecchio
  • Article
    | Open Access

    Gravitational wave sources can be used as cosmological probes through a direct distance luminosity relation. Here, the authors demonstrate that the time delay between lensed gravitational wave signals and their electromagnetic counterparts can reduce the uncertainty in the Hubble constant.

    • Kai Liao
    • , Xi-Long Fan
    •  & Zong-Hong Zhu
  • Review Article |

    Gravitational waves are predicted by general relativity, but their direct observation from astronomical sources hinges on large improvements in detection sensitivity. The authors review how squeezed light and other quantum optical concepts are being applied in the development of next generation interferometric detectors.

    • Roman Schnabel
    • , Nergis Mavalvala
    •  & Ping K. Lam