Study Uses Stars Orbiting Sagittarius A* to Constrain the Cosmological Constant
Researchers have used the orbits of three stars near the supermassive black hole Sgr A* to place upper bounds on the cosmological constant Λ at the Galactic Center. The study modeled stellar motion using Schwarzschild-de Sitter spacetime and applied Bayesian MCMC analysis to astrometric and spectroscopic data from stars S2, S1, and S14. The results provide a rare local measurement of a quantity typically constrained only at cosmological scales, testing whether Λ is consistent across vastly different physical environments.
A new preprint posted to arXiv presents constraints on the cosmological constant Λ derived from observations of stars orbiting Sgr A*, the supermassive black hole at the center of the Milky Way. The researchers modeled the trajectories of three well-studied stars — S2, S1, and S14 — by numerically integrating timelike geodesics in Schwarzschild-de Sitter spacetime, a framework that incorporates both black hole gravity and a cosmological constant. Relativistic effects including gravitational redshift and Shapiro time delay were included in the modeling. A Bayesian Markov Chain Monte Carlo (MCMC) analysis was used to infer orbital and spacetime parameters and produce posterior distributions for Λ. Combining constraints from all three stellar orbits, the study yields upper bounds of Λ ≲ 6.9×10⁻⁴⁸ m⁻² at 68% credibility and Λ ≲ 1.0×10⁻³⁸ m⁻² at 95% credibility. These bounds are weaker than the globally accepted cosmological value of approximately 1.1×10⁻⁵² m⁻², but represent an independent, local test of whether the cosmological constant manifests consistently at Galactic Center scales.
What's missing
The study's own key limitation is that its upper bounds on Λ are several orders of magnitude weaker than the cosmological value inferred from large-scale structure and CMB observations, meaning the results cannot confirm or tightly constrain the accepted value — only rule out very large deviations. As a preprint, the work has not yet undergone peer review.
What different sources said
- arXiv astro-phCenter
Bounds on $\Lambda$ at the Galactic Center
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