Dark Energy: No Longer a Surprise

A bit of science news: Alexey Vikhlinin and collaborators have used observations from the Chandra X-ray satellite to uncover new evidence for dark energy. (More info here, and the paper is here.) In particular, they simply count the number of galaxy clusters with various masses at various redshifts, and compare with the predictions of models with and without dark energy. If there were no dark energy, matter would keep clustering on larger and larger scales as the universe expanded, making new clusters all the way. But if dark energy eventually takes over, the creation of new clusters begins to turn off, as the dark energy provides an extra push of expansion beneath the feet of the particles that would like to cluster together, preventing them from doing so. Just to guide the eye, here are plots of the number of clusters (vertical axis) as a function of their mass (horizontal ...