Universe's Expansion Measured to Extreme Precision

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Scientists studying more than 140,000 extremely bright galaxies have calculated the expansion of the universe with unprecedented accuracy.

Dark energy and dark matter account for most of the universe, but what are these elusive phenomena?
NASA/JPL/Hubble

The distant galaxies, known as quasars, serve as a "standard ruler" to map density variations in the universe. Physicists were able to extend their calculations almost twice as far back in time as has been previously accomplished.

Using the Baryon Oscillation Spectroscopic Survey (BOSS), two teams of physicists have improved on scientists' understanding of the mysterious dark energy that drives the accelerating universe. By nearly tripling the number of quasars previously studied, as well as implementing a new technique, the scientists were able to calculate the expansion rate to 42 miles (68 kilometers) per second per 1 million light-years with greater precision, while looking farther back in time. [8 Baffling Astronomy Mysteries]

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Andreu Font-Ribera, of the U.S. Department of Energy's Lawrence Berkeley National Laboratory, led one of the two teams, while Timothée Delubac of EPFL, Switzerland, and France’s Centre de Saclay headed the other one. Font-Ribera presented the new findings in April at a meeting of the American Physical Society in Savannah, Georgia.

The new research "explores a region of the universe that was not explored before," Font-Ribera said.

Stretching the Standard Ruler

The expanding universe stretches light waves as they travel through it, a process astronomers refer to as redshifting. An object's physical distance from the observer depends on how quickly the universe is expanding.

ANALYSIS: Most Precise Measurement of Scale of the Universe

Baryon acoustic oscillations (BAOs) are sound waves imprinted in large structures of matter in the early universe. Competing forces of inward-pushing gravity and outward, heat-related pressure cause oscillations similar to sound waves in the baryonic, or "normal" matter in the universe.

Dark matter, which interacts with normal matter only gravitationally, stays at the center of the sound wave, while the baryonic matter travels outward, eventually creating a shell at a set radius known as the sound horizon.

Quasars, like other galaxies, are surrounded by dust. Light leaving galaxies streams through that dust, revealing the imprint of the BAOs. Studying this light allows researchers to map the distribution of quasars, as well as the gas in the early universe.

By using BOSS, the largest component of the third Sloan Digital Sky Survey, to map BAOs, scientists can determine how matter is distributed in the early universe. When it comes to measuring the expansion of the universe, BAOs serve as a "standard ruler."

"We think we know its size, and its apparent size depends on how far away it is," Patrick McDonald, of the Canadian Institute for Theoretical Astrophysics, said at the conference.