Gravitational redshift of galaxies in clusters as predicted by general relativity

TL;DR

This paper reports the first observational detection of gravitational redshift in galaxy clusters, confirming general relativity's predictions on cosmological scales and challenging alternative gravity models.

Contribution

It provides the first empirical measurement of gravitational redshift in galaxy clusters, testing general relativity independently of the b1CDM model assumptions.

Findings

Observation confirms general relativity's predictions at 99% confidence level.

Results are inconsistent with alternative gravity models without dark matter.

Supports the validity of general relativity on large cosmological scales.

Abstract

The theoretical framework of cosmology is mainly defined by gravity, of which general relativity is the current model. Recent tests of general relativity within the \Lambda Cold Dark Matter (CDM) model have found a concordance between predictions and the observations of the growth rate and clustering of the cosmic web. General relativity has not hitherto been tested on cosmological scales independent of the assumptions of the \Lambda CDM model. Here we report observation of the gravitational redshift of light coming from galaxies in clusters at the 99 per cent confidence level, based upon archival data. The measurement agrees with the predictions of general relativity and its modification created to explain cosmic acceleration without the need for dark energy (f(R) theory), but is inconsistent with alternative models designed to avoid the presence of dark matter.