Bounds on $\Lambda$ at the Galactic Center

Abstract

We constrain the cosmological constant, $\Lambda$, using astrometric and spectroscopic observations of the S2 star, supplemented by S1 and S14 stars orbiting Sgr A${}^{\ast }$. We develop a framework for modelling relativistic stellar orbits in general spherically symmetric spacetimes and perform Bayesian parameter estimation to jointly infer orbital and spacetime parameters. Applying this framework to Schwarzschild-de Sitter spacetime, we obtain upper bounds on $\Lambda$. The individual constraints exhibit the expected dependence on the dynamical timescales of the stars, with the longer-period S1 providing the strongest sensitivity. Combining the individual constraints, we obtain $\Lambda \lesssim 6.9\times 10^{-48}{\mathrm{m}}^{-2}$ at 68\% credibility and $\Lambda \lesssim 1.0\times 10^{-38}{\mathrm{m}}^{-2}$ at 95\% credibility. The 68\% constraint is the strongest bound at a comparable dynamical timescale.

arXiv comment27 pages, 9 figures