Bounds on Λ at the Galactic Center

We constrain the cosmological constant $\Lambda$ using astrometric and spectroscopic observations of the S2, S1, and S14 stars orbiting Sgr A$^*$. The stellar motion is modelled by numerically integrating timelike geodesics in Schwarzschild-de Sitter spacetime, including relativistic redshift and time-delay corrections. Orbital and spacetime parameters are inferred using a Bayesian MCMC analysis. The resulting posterior distributions place upper bounds on the magnitude of $\Lambda$ at the Galactic Center (GC). Combining the independent constraints from the S2, S1, and S14 orbits yields upper bounds of $\Lambda \lesssim 6.9\times10^{-48} \mathrm{m}^{-2}$ at 68\% credibility and $\Lambda \lesssim 1.0\times10^{-38} \mathrm{m}^{-2}$ at 95\% credibility.