Probing the Anisotropic Universe with Gravitational Waves
  Modern cosmology rests on the working assumption that the Universe is
isotropic and homogeneous at large scales. Here, we document a number of
anomalous observations pointing to an anisotropic Universe in a direction
consistent with the CMB dipole. If physical, this should be confirmed by any
cosmological probe with sufficient data quality. To that end, we perform the
first hemispherical decomposition of bright and dark standard siren $H_0$
determinations, finding that the maximum of the $H_0$ posterior is larger in
the CMB dipole direction for dark sirens, but including the bright siren
posterior reverses this conclusion. As may be expected, the limited number of
GW observations is consistent with an isotropic Universe, but this can change
going forward. It is imperative to repeat these tests as GW sources become more
numerous and better localised.
