Dark energy measured with huge 3D map
26 Jul 2016 by hjqbcptqcm.d hjqbcptqcm.d
A 3D map of more than one million galaxies has been created to measure the effects of dark energy on the Universe’s expansion
A 3D map of more than one million galaxies has been created to measure the effects of dark energy on the Universe’s expansion.
The physicists and astronomers spent five years collecting measurements of 1.2m galaxies with a volume of more than 650 cubic billion light years. They were carried out by the Baryon Oscillation Spectroscopic Survey (BOSS) programme of the Sloan Digital Sky Survey-III (SDSS-III).
David Schlegel, principal investigator for BOSS, said: “We’ve made the largest map for studying the 95% of the universe that is dark. In this map, we can see galaxies being gravitationally pulled towards other galaxies by dark matter. And on much larger scales, we see the effect of dark energy ripping the universe apart.”
BOSS measures the expansion rate of the Universe by measuring the size of baryonic acoustic oscillations (BAO). BAO size is determined by pressure waves that travelled through the Universe until it was 400,000 years old, when they were frozen in the matter distribution of the Universe. Researchers calculated the size of these waves generated 13.4 billion years ago in the cosmic microwave background. By measuring the distribution of galaxies since, researchers can measure how dark energy and matter have competed, causing the rate of expansion.
Ariel Sanchez, an astrophysicist at Berkeley Lab in California, responsible for leading the efforts to calculate exact amounts of dark matter and energy based on BOSS data, said: “Measuring the acoustic scale across cosmic history gives a direct ruler with which to measure the Universe’s expansion rate. With BOSS, we have traced the BAO’s subtle imprint on the distribution of galaxies spanning a range of time from 2 to 7 billion years ago.”
The movement of galaxies towards regions of the Universe, due to the attractive force of gravity, can be seen on this map. This movement is explained by predictions of general relativity.
The papers describing this survey were published in the Monthly Notices of the Royal Astronomical Society.
