Astronomers Measure Distance to Neighboring Galaxy with Greater Accuracy

The measurement of distance to our neighboring galaxy, the large Magellanic Cloud(LMC), was sharpened to an accuracy of 2%, astronomers claim.

This is the more accurate this distance has ever been measured, and it scientists accomplished it using binary stars as a standard for reference.

The measurement has revealed that the irregular galaxy is about 163,000 light-years away. It will allow scientists to more accurately determine distances to farther objects and assess the actual rate of the universe's expansion, by improving knowledge of the Hubble Constant.

"I am very excited because astronomers have been trying for a hundred years to accurately measure the distance to the Large Magellanic Cloud, and it has proved to be extremely difficult," says Wolfgang Gieren of the Universidad de Concepción, Chile. "Now we have solved this problem by demonstrably having a result accurate to two percent."

Scientists rely on measurements of close-by objects and use them as standard candles to pin down distances further and further out into the cosmos and therefore survey the scale of the universe.

The distance to stars in the Large Magellanic Cloud is particular important in that sense because they are used to fix the scale for more remote galaxies.

The astronomers managed this by observing rare close pairs of stars, known as eclipsing binaries. When one passes in front of the other, as seen from Earth, the total brightness drops.

By surveying these changes in brightness very carefully, and by measuring the stars' orbital speeds, it is possible to work out how big the stars are, their masses and other information about their orbits. When this is combined with careful measurements of the total brightness and colors of the stars, remarkably accurate distances can be found.

This method has been used before, but with hot stars - which requires certain assumptions to be made, and gives less accurate results. But now, for the first time, eight extremely rare eclipsing binaries where both stars are cooler red giant stars have been identified, which can yield much more accurate distance values - accurate to about two percent.

"We are working to improve our method still further and hope to have a one percent LMC distance in a very few years from now," says Dariusz Graczyk of Warsaw University Observatory. "This has far-reaching consequences not only for cosmology, but for many fields of astrophysics."