Astronomers have announced the most precise results on the expansion of the universe and dark energy yet. This feat was possible by using Sloan Digital Sky Survey, an automated system, which has collected data on 1.2 million galaxies.
Hundreds of scientists from all over the world collaborated to create the largest-ever three-dimensional map of the cosmos, looking at galaxies between 2 and 7 billion light-years away.
"We have spent a decade collecting measurements of 1.2 million galaxies over one-quarter of the sky to map out the structure of the universe over a volume of 650 cubic billion light-years," said Jeremy Tinker of New York University, a co-leader of the scientific team that led this effort, in a statement.
"This map has allowed us to make the best measurements yet of the effects of dark energy in the expansion of the universe. We are making our results and map available to the world."
The project is called BOSS – Baryon Oscillation Spectroscopic Survey (excellent acronym work here) – and it uses how galaxies are distributed in the universe to estimate the size of baryonic acoustic oscillations.
These oscillations were formed by pressure waves (like sound, hence the "acoustic") in the matter distribution of the universe when it was 400,000 light-years old, at which point they froze, creating slight overdensities and underdensities of galaxies across space.
"If we were to scale the volume of our survey to a cube 1 mile on each side, then the visible part of an individual galaxy would be about 1 millimeter across," explained Rita Tojeiro of the University of St. Andrews, the other co-leader of the BOSS galaxy clustering working group.
"Our challenge in the analysis of this map was equivalent to measuring the distances between all the pairs of galaxies separated by 100 yards throughout a cubic mile of space!"
By having such detailed map of such a large number of galaxies, the team was able to create a unique ruler to measure how the universe expansion rate has changed over time. The latest estimate put the expansion rate to 67.3 kilometers per second per Megaparsec, which is well in agreement with the standard cosmological model. Thirteen papers detailing the new discoveries have been released online.
The map has also revealed that the large structures in the universe move as predicted by general relativity, supporting the idea that dark energy is mysterious but real, rather than our gravitational theories being wrong.
This is a section of the three-dimensional map constructed by BOSS. The rectangle on the far left shows a cutout of 1000 sq. degrees in the sky containing nearly 120,000 galaxies, or roughly 10% of the total survey. Jeremy Tinker and the SDSS-III collaboration.