An international team of astronomers – co-led by Dr. Rita Tojeiro from the University of St Andrews – have produced the largest-ever three-dimensional map of the universe. The creation of the map was done as a collaboration between hundreds of scientists from the Sloan Digital Sky Survey III (SDSS-III). It was then used to make one of the most precise measurements of the dark energy currently driving the accelerated expansion of the Universe.
The study took place over the course of a decade, measuring the positions of 1.2 million galaxies. It resulted in mapping the three-dimensional structure of the universe over a volume of 650 cubic billion light years. The measurements were carried out by the Baryon Oscillation Spectroscopic Survey program of the SDSS-III.
The record-breaking map allows astronomers to measure the expansion rate of the universe, and determine the amount of it made up of matter and dark energy. These measurements are made by determining the size of the baryonic acoustic oscillations (BAO) in the three-dimensional distributions of galaxies. The original BAO size is determined by pressure waves that travelled through the young universe up to when it was only 400,000 years old (the universe is now 13.8 billion years old), at which point they became frozen in the matter distribution of the universe. The end result is that galaxies are preferentially separated by a characteristic distance that astronomers call the acoustic scale. Measuring the distribution of galaxies from the time when pressure waves became frozen allows astronomers to reflect how dark matter and dark energy have competed to govern the rate of expansion of the universe.
To measure the precise size of ancient waves, BOSS had to create an ambitious galaxy map. The map reveals the coherent movement of galaxies towards regions of the universe with more matter due to gravity. This supports the idea that the acceleration of the expansion rate is driven by a cosmic phenomenon such as dark energy.