A precise extragalactic test of General Relativity

TL;DR

This paper tests Einstein's General Relativity on extragalactic scales using gravitational lensing and stellar kinematics, finding results consistent with GR's predictions and constraining the weak-field metric of gravity beyond the Solar System.

Contribution

It introduces a novel method combining lensing and stellar dynamics to measure the spatial curvature parameter gamma in an extragalactic setting.

Findings

Measured gamma = 0.97 ± 0.09, consistent with GR

Provided the first strong extragalactic constraint on the weak-field metric

Demonstrated the effectiveness of combined lensing and kinematic analysis

Abstract

Einstein's theory of gravity, General Relativity, has been precisely tested on Solar System scales, but the long-range nature of gravity is still poorly constrained. The nearby strong gravitational lens, ESO 325-G004, provides a laboratory to probe the weak-field regime of gravity and measure the spatial curvature generated per unit mass, $\gamma$. By reconstructing the observed light profile of the lensed arcs and the observed spatially resolved stellar kinematics with a single self-consistent model, we conclude that $\gamma = 0.97 \pm 0.09$ at 68% confidence. Our result is consistent with the prediction of 1 from General Relativity and provides a strong extragalactic constraint on the weak-field metric of gravity.