The largest 3D map of distant galaxies ever made has allowed one of the most precise measurements yet of dark energy, which is currently driving the accelerating expansion of the universe. The new measurements, which were carried out by the Baryon Oscillation Spectroscopic Survey (BOSS) programme of the Sloan Digital Sky Survey-III, took five years to make and include 1.2 million galaxies over one quarter of the sky – equating to a volume of 650 cubic billion light-years.
BOSS measures the expansion rate by determining the size of baryonic acoustic oscillations, which are remnants of primordial acoustic waves. “We see a dramatic connection between the sound-wave imprints seen in the cosmic microwave background to the clustering of galaxies 7–12 billion years later,” says co-leader of the BOSS galaxy-clustering working group Rita Tojeiro. “The ability to observe a single well-modelled physical effect from recombination until today is a great boon for cosmology.”
The map shows galaxies being pulled towards each other by dark matter, while on much larger scales it reveals the effect of dark energy ripping the universe apart. It also reveals the coherent movement of galaxies toward regions of the universe with more matter, with the observed amount of in-fall explained well by general relativity. The results have been submitted to the Monthly Notices of the Royal Astronomical Society.