EarthSky // Science Wire, Space Release Date: Apr 07, 2014

A new analysis says that 10.8 billion years ago, the universe was expanding by one percent every 44 million years.


Artist’s conception of how BOSS uses quasars to measure the distant universe. Via Zosia Rostomian (Lawrence Berkeley National Laboratory) and Andreu Font-Ribera (BOSS Lyman-alpha team, Berkeley Lab.)

Astronomers from the Sloan Digital Sky Survey have used 140,000 distant quasars to measure the expansion rate of the universe when it was only one-quarter of its present age. This is the best measurement yet of the expansion rate at any epoch in the last 13 billion years.

The Baryon Oscillation Spectroscopic Survey (BOSS), the largest component of the third Sloan Digital Sky Survey (SDSS-III), pioneered the technique of measuring the structure of the young universe by using quasars to map the distribution of intergalactic hydrogen gas. Today, new BOSS observations of this structure were presented at the April 2014 meeting of the American Physical Society in Savannah, GA.

These latest results combine two different methods of using quasars and intergalactic gas to measure the rate of expansion of the universe. The first analysis, by Andreu Font-Ribera (Lawrence Berkeley National Laboratory) and collaborators, compares the distribution of quasars to the distribution of hydrogen gas to measure distances in the universe. A second analysis team led by Timothee Delubac (Center de Saclay, France) focused on the patterns in the hydrogen gas itself to measure the distribution of mass in the young universe. Together the two BOSS analyzes establish that 10.8 billion years ago, the universe was expanding by one percent every 44 million years.

“If we look back to the universe when galaxies were three times closer together than they are today, we’d see that a pair of galaxies separated by a million light-years would be drifting apart at a speed of 68 kilometers per second as the universe expands,” says Font-Ribera.

Delubac explains that “we have measured the expansion rate in the young universe with an unprecedented precision of 2 percent.” Measuring the expansion rate of the universe over its entire history is key in determining the nature of the dark energy that is responsible for causing this expansion rate to increase during the past six billion years. “By probing the universe when it was only a quarter of its present age, BOSS has placed a key anchor to compare to more recent expansion measurements as dark energy has taken hold,” says Delubac.

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