Constraining Dark Energy from the Local Group Dynamics

Abstract This Letter develops a method to constrain the cosmological constant Λ from binary galaxies, focusing on Milky Way and Andromeda galaxies. We provide an analytical solution two-body problem with show that ratio between Keplerian period T Λ = 2 π / stretchy="false">( c stretchy="false">) ≈ 63.2 Gyr controls importance of effects constant. The Andromeda–Milky orbit has ∼17 Gyr, so dark energy be taken into account. Using current best mass estimates we find value upper bound is 5.44 times obtained by Planck. With future astrometric measurements, can reduced $\left(1.67\pm 0.79\right){{\rm{\Lambda }}}_{\mathrm{PL}}$?> 1.67 ± 0.79 PL . Our results offer prospects constraints over very different scales than previously. Local Group provides also completely novel platform test alternative theories gravity. illustrate this deriving bounds scalar-tensor gravity megaparsec scales.