Hubble precisely measures distance to globular star cluster

Astronomers using NASA's Hubble Space Telescope have for the first time precisely measured the distance to one of the oldest objects in the universe — a collection of stars born shortly after the Big Bang. This stellar assembly, a globular star cluster called "NGC 6397", is one of the closest such clusters to Earth. The new measurement sets the cluster's distance at 7,800 light-years away, with just a three per cent margin of error.

This new distance yardstick provides an independent estimate for the age of the universe, the US space agency said in a statement on Thursday. The new measurement will also help astronomers improve models of stellar evolution.

Star clusters are the key ingredient in stellar models because the stars in each grouping are at the same distance, have the same age, and have the same chemical composition. The new measurement uses straightforward trigonometry, the same method used by surveyors, and as old as classical Greek science. The research team calculated NGC 6397's age at 13.4 billion years old. "The globular clusters are so old that if their ages and distances deduced from models are off by a little bit, they seem to be older than the age of the universe," said Tom Brown of the Space Telescope Science Institute (STScI) in Baltimore, Maryland

The researchers say they could reach an accuracy of one per cent if they combine the Hubble distance measurement of NGC 6397 with the upcoming results obtained from the European Space Agency's Gaia space observatory.

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"Getting to one per cent accuracy will nail this distance measurement forever," Brown said. The findings appeared in The Astrophysical Journal Letters. IANS