Previously, astronomers have used BAOs to measure the distances to galaxies in order to determine the distribution of mass in the universe, and thus the universe's expansion rate. But galaxies grow fainter at greater distances, so previous studies were limited to looking back only 6 billion light-years into the universe's 13.8-billion-year lifetime.
Font-Ribera and his team, which included McDonald, pioneered a method of measuring BAOs by using quasars, which are galaxies that are far brighter than normal due to the activity of a supermassive black hole at their center. As matter falls into the black hole, it grows extremely hot, radiating light at far brighter wavelengths and over farther distances than conventional galaxies. This allowed the scientists to measure the mass distribution of the universe out to 12 billion years.
Font-Ribera's research involved approximately 50,000 quasars. The new study published by Delubac's team reviewed nearly three times as many sources, more precisely calculating the expansion rate to an accuracy of 2.2 percent. [See images of dark matter in the universe]
"If we looked back to the universe when it was less than a quarter of its present age, we'd see that a pair of galaxies separated by a million light-years would be drifting apart at a velocity of 68 kilometers a second as the universe expands," Font-Ribera said in an accompanying press release.
"The uncertainty is plus or minus only a kilometer and a half per second."
The Expanding Universe
In the early twentieth century, astronomer Edwin Hubble determined that the galaxies in the universe are all moving away from the Milky Way because the universe is expanding. Further studies led astronomers to conclude that the rate of expansion is speeding up rather than slowing down.
McDonald compared the process to a ball thrown in the air.
"Acceleration is like you throw the ball up, and it starts going up faster and faster," McDonald said. "No normal attractive gravity will do that."
Astronomers determined that an unseen force, dubbed "dark energy," causes the acceleration. McDonald calls dark energy a "placeholder" because scientists aren't certain what, precisely, it is.
"To me, it seems quite possible that it's related to some fundamental hole in our understanding of physics," he said.
In order to patch that hole, scientists must continue to learn more about dark energy, including its role in accelerating the expansion of the universe.
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