After spending a decade measuring the stars, scientists just released a 3D map spanning 1.2 million galaxies. But it also measures the universe's expansion over time, giving credence to the theory that dark energy played a role in its increasing size.
Hundreds of scientists from the Baryon Oscillation Spectroscopic Survey (BOSS), a program from the Sloan Digital Sky Survey III that measures the expansion of the universe over time, collaborated to make the map. The full one spans 650 cubic billion light-years, which is about a quarter of the sky.
The above image, however, is only a slice of it, covering 1/20th of the sky and ranging only 6 billion light-years wide. Color indicates distance from Earth, with yellow dots representing the nearest galaxies and purple the farthest away (grey dots are regions that weren't surveyed). Inside are 48,741 galaxies, about 3 percent of the full dataset, meaning they observed 1,624,700 in total.
BOSS tracked the universe's increasing size by tracking pressure waves that emanated out from the Big Bang and froze as matter solidified 400,000 years later. The researchers tracked galactic movement from 7 billion years ago until 2 billion years ago, which supports dark energy's and dark matter's roles in the universe's growth. Measuring the distribution of galaxies across time reveals how much both elements competed to increase its outward expansion in the time period they tracked.
"If dark energy has been driving the expansion of the Universe over that time, our maps tell us that it is evolving very slowly if at all: the change is at most 20% over the past seven billion years," said Florian Beutler of University of Portsmouth, who contributed two of the papers that the scientists submitted to the Monthly Notices of the Royal Astronomical Society this week.