Our universe may be 15% larger and older than we thought, according to new measurements of the distance to a nearby galaxy.

Researchers led by Alceste Bonanos at the Carnegie Institution of Washington, US, used data from telescopes including the 10-metre Keck-II telescope in Hawaii, US, to measure the distance to a pair of stars in the Triangulum Galaxy.

The team used light, velocity, and temperature measurements to calculate the true luminosity of the two stars, which eclipse one another every five days. By comparing this intrinsic luminosity to their observed brightness, the team calculated that the galaxy lies 3.14 million light years away from us. Surprisingly, this is about half a million light years farther than previously thought.

Measuring astronomical distances is not simple. Distant, bright objects, for example, can look the same as closer, dim ones. So astronomers have built a ladder-like system that starts by using several independent methods to accurately determine the distance to nearby objects. They then use these measurements to define a more distant cosmic yardstick, and so on.

“In every step, you accumulate errors,” says team member Krzysztof Stanek at Ohio State University in Columbus, US. “We wanted an independent measure of distance – a single step that will one day help with measuring dark energy and other things.”

Hubble constant

Gauging distances by observing a binary star has cut out those extra steps, says team member Norbert Przybilla at the University of Erlangen-Nuremberg, Germany. "This is the farthest distance that anyone has been able to measure directly," he told New Scientist. "It's the cutting edge of what can be done with these telescopes."

Earlier measurements were based on calculations using the Hubble constant, a measure of the expansion rate and age of the universe. The new observation implies that the value used for the constant is off by 15%, says Przybilla.

That suggests the universe is 15% larger, and 15% older than previously thought. Recent estimates have put the age of the universe at 13.7 billion years, and the new research suggests it may actually be 15.8 billion years old.

"Our result hints that there may be something interesting happening with the Hubble constant," says Przybilla. But he cautions that the study reports only one distance measurement. "We need to follow this up with more measurements."

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