Dark energy as a critical period in binary motion: Bounds from multi-scale binaries

The two-body problem under the influence of both dark energy and post-Newtonian modifications is studied. In this unified framework, we demonstrate that dark energy plays the role of a critical period with T-Lambda=2 pi/c root Lambda approximate to 60 Gyr. We also show that the ratio between orbital and critical period naturally emerges from the Kretschmann scalar, which is a quadratic curvature invariant characterizing all binary systems effectively represented by a de Sitter-Schwarzschild spacetime. The suitability of a binary system to constrain dark energy is determined by the ratio between its Keplerian orbital period TK and the critical period T-Lambda. Systems with T-K approximate to T-Lambda are optimal for constraining the cosmological constant Lambda, such as the Local Group and the Virgo Cluster. Systems with T-K << T-Lambda are dominated by attractive gravity (which are best suited for studying modified gravity corrections). Systems with T-K >> T-Lambda are dominated by repulsive dark energy and can thus be used to constrain Lambda from below. We use our unified framework of post-Newtonian and dark-energy modifications to calculate the precession of bounded and unbounded astrophysical systems and infer constraints on Lambda from them. Pulsars, the solar system, S stars around Sgr A*, the Local Group, and the Virgo Cluster, having orbital periods of days to gigayears, are analyzed. The results reveal that the upper bound on the cosmological constant decreases when the orbital period of the system increases, emphasizing that Lambda is a critical period in binary motion.