Astronomers measure far-off galaxies to 1 percent precision

Peter Kelley UW News

University of Washington astronomers and colleagues have measured the distance to galaxies six billion light-years away — about halfway back to the Big Bang — to an accuracy of just 1 percent.

The Sloan Digital Telescope measurement also may aid in understanding the mysterious force, often called “dark energy,” thought to be accelerating the expansion of the universe.

The findings come from the Baryon Oscillation Spectroscopic Survey, the largest of four projects that together comprise the Sloan Digital Sky Survey III, conducted by a consortium of about four dozen universities at the Sloan Foundation’s telescope at Apache Point Observatory in New Mexico.

“We know the universe started much smaller and is currently expanding, but we don’t know much about the history of that expansion,” said Lauren Anderson, a UW astronomy doctoral student and first author of a paper presented at the annual meeting of the American Astronomical Society in Washington, D.C.

“The light we measure from a galaxy carries the information of how much the space between us and the galaxy grew. Then, pinning down the physical distance to that galaxy tells us the average expansion history of that chunk of space,” Anderson said. Measuring that rate of expansion, she added, is astronomers’ best way to learn about the dark energy apparently causing the expansion of the universe to speed up.

Such precise measurements from billions of light-years away require a different technique than those used to measure planets in the solar system or the Milky Way. This survey measures “baryon acoustic oscillations,” or occasional ripples in the distribution of galaxies in the universe. The ripples are imprints of pressure waves that moved through the early universe, and can be measured today by mapping galaxies. The size of these imprints can be used as a standard ruler to measure distances.

The new analysis covers an area twice as large and with greater accuracy than earlier mapping in 2013. The work also includes the first measurements from a sample of nearby galaxies.

“Making these measurements at two different distances allows us to see how the expansion of the universe has changed over time, which will help us understand why it is accelerating,” said co-author Rita Tojeiro of the University of Portsmouth in the U.K.

UW work on the project included assistance with data management by Anderson and graduate student and co-author Vaishali Bhardwaj, and the drilling of aluminum plates used to hold in place the fiber optic cables that collect the light from each targeted galaxy.

Funding for the Sloan Digital Sky Survey III was provided by the Alfred P. Sloan Foundation, the National Science Foundation, the U.S. Department of Energy Office of Science and participating institutions.

“There are not many things in our daily life that we know to 1-percent accuracy,” said David Schlegel, a physicist at Lawrence Berkeley National Laboratory and the Baryon Oscillation Spectroscopic Survey’s principal investigator.

“I now know the size of the universe better than I know the size of my house.”

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This article was based in part on a news release by the consortium of institutions participating in the Sloan Digital Sky Survey III. For more information on UW participation in this work, contact Anderson at 206-543-9584 or lmanders@astro.washington.edu.