Possibility of Detecting Anisotropic Expansion of the Universe by Very Accurate Astrometry Measurements

Refined astrometry measurements allow us to detect large-scale deviations from isotropy through real-time observations of changes in the angular separation between sources at cosmic distances. This “cosmic parallax” effect is a powerful consistency test of the Friedmann-Robertson-Walker metric and may set independent constraints on cosmic anisotropy. We apply this novel general test to Lemaitre-Tolman-Bondi cosmologies with off-center observers and show that future satellite missions such as Gaia might achieve accuracies that would put limits on the off-center distance which are competitive with cosmic microwave background dipole constraints.

Figure 1

Overview, notation, and conventions. For clarity, we assumed here that the points $C$, $O$, $a_1$, $b_1$, $a_2$, $b_2$ all lie on the same plane. Comoving coordinates $r$ and $r_0$ correspond to physical coordinates $X$ and $X_0$.

Figure 2

${\Delta }_t\gamma$ for three sources at the same shell, at $z=1$, for both model I (full lines) and model II (dashed lines), and the FRW-like estimate (dotted lines). As expected, ${\Delta }_t\gamma$ is linear in $\Delta \theta$.