Gravitational redshift of galaxies in clusters as predicted by general relativity

• Published in: Nature (London) 2011-09, Vol.477 (7366), p.567-569
• Main Authors: Wojtak, Radosław, Hansen, Steen H., Hjorth, Jens
• Format: Article
• Language: English
• Subjects: 639/766/33/34/863; Astrophysics; Humanities and Social Sciences; letter; multidisciplinary; Science; Science (multidisciplinary); Stars & galaxies; Universe
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature10445

Cosmic-scale test for general relativity Testing general relativity on the large scales of the Universe remains a fundamental challenge to modern cosmology. The theoretical framework of cosmology is defined by gravity, for which general relativity is the current model. Wojtak et al . now show that a classical test of general relativity — the gravitational redshift experienced by photons propagating outwards from a gravitational potential well — provides a direct means of testing gravity on scales of several megaparsecs, independent of cosmology. Their observations of the gravitational redshift of light coming from galaxies in clusters at the 99% confidence level agree with the predictions of general relativity, and are inconsistent with alternative models designed to avoid the presence of dark matter. 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 (ΛCDM) model have found a concordance between predictions and the observations of the growth rate and clustering of the cosmic web 1 , 2 . General relativity has not hitherto been tested on cosmological scales independently of the assumptions of the ΛCDM model. Here we report an observation of the gravitational redshift of light coming from galaxies in clusters at the 99 per cent confidence level, based on archival data 3 . Our measurement agrees with the predictions of general relativity and its modification created to explain cosmic acceleration without the need for dark energy (the f ( R ) theory 4 ), but is inconsistent with alternative models designed to avoid the presence of dark matter 5 , 6 .