General Relativity Holds Up Under Galactic Test

Yesterday’s trip to the dark side involved the so-called ‘dark flow,’ the apparent motion of galactic clusters along a path in the direction of the constellations Centaurus and Hydra. Today we look at two other dark conjectures — dark matter and dark energy. Are both a part of the universe we observe, or can we do away with them by clever manipulation of Einstein’s theory of general relativity? The latest word, from an international team of researchers studying the clustering of more than 70,000 galaxies, is that GR seems to have passed yet another test. This is useful stuff, because one of the implications is that dark matter is the most likely explanation of the movement of galaxies and galaxy clusters as they seem to respond to an unseen mass.
The possibility of dark matter was noted as long ago as 1933 by Fritz Zwicky, who studied the average mass of galaxies within the Coma cluster and obtained a value much higher than expected from their luminosity. Later studies of individual galaxies made it clear that a halo of dark matter would explain anomalous galactic rotations. But all that assumed no changes to general relativity at cosmological scales.

Image: A ...