Study Uses Stars Orbiting Sagittarius A* to Constrain the Cosmological Constant
Researchers used observations of three stars (S2, S1, and S14) orbiting the supermassive black hole Sagittarius A* to place upper limits on the cosmological constant Lambda at the Galactic Center. The analysis employed Bayesian statistical methods to model stellar orbits in Schwarzschild-de Sitter spacetime, accounting for relativistic effects. This work demonstrates how precision astrometry of extreme gravitational environments can test fundamental cosmological parameters.
A new study constrains the cosmological constant Lambda—a key parameter in Einstein's equations describing cosmic expansion—by analyzing the orbital dynamics of stars near Sagittarius A*, the supermassive black hole at the Milky Way's center. The researchers modeled the motion of three stars (S2, S1, and S14) using general relativity in Schwarzschild-de Sitter spacetime, incorporating relativistic redshift and time-delay corrections. Using Bayesian MCMC analysis of astrometric and spectroscopic data, they derived upper bounds on Lambda: approximately 6.9×10⁻⁴⁸ m⁻² at 68% credibility and 1.0×10⁻³⁸ m⁻² at 95% credibility. The independent constraints from each star's orbit were combined to strengthen the overall limits. This approach leverages the extreme gravitational environment near a black hole to test cosmological theory at scales where relativistic effects are pronounced.
What's missing
The study does not discuss how these local Galactic Center constraints compare quantitatively to cosmological constant measurements from other methods (e.g., cosmic microwave background, supernovae, baryon acoustic oscillations), or whether the methodology could be extended to other galactic nuclei. The paper also does not address potential systematic uncertainties from stellar mass estimates, distance measurements, or assumptions about the spacetime geometry beyond Schwarzschild-de Sitter.
What different sources said
- arXiv astro-phCenter
Bounds on $\Lambda$ at the Galactic Center
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