10,000 Suns at the Heart of the Milky Way All Move at Their Own Speed

Astronomers wading through nine years' worth of data from 10,000 stars at the heart of our galaxy have been able to map their paths to better understand how stars in the densest neighborhood of the Milky Way behave. The team of scientists reported on the project in a preprint paper they are presenting this week at the annual conference of the American Astronomical Society.

The galaxy's core, also known as the Milky Way's bulge, is about 26,000 light-years away from us here on Earth. Astronomers had thought most of its stars were fairly old, but because it's so jam-packed, the region has always been a challenge to study.

01_11_milky_way_bulge The Milky Way as it appears from the edge of the galaxy. ESO/S. Brunier/Flickr

For the new research, scientists turned to the Hubble Space Telescope to look for stars that are fairly similar to our own sun. 

"Hubble gave us a narrow, pencil-beam view of the galaxy’s core, but we are seeing thousands more stars than those spotted in earlier studies," Annalisa Calamida, an astronomer at the Space Telescope Science Institute, said in a press release.

Earlier studies looking at the galactic bulge focused on brighter stars, which were easier to pick up but older and less common. The new work instead prioritized quantity, analyzing nine years' worth of Hubble data to track individual stars—10,000 of them—about the size of our sun. By pairing that information with the stars' chemical composition, which relates to a star's age, the team could pick out patterns in the data.

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They found that younger stars move twice as fast as older stars, suggesting that the galactic center is much more hectic than scientists had expected.

The results also suggest that not all of the bulge's resident stars are as old as scientists had thought they would be if the galactic core was born when the galaxy itself first formed.

The results don't quite match either of the leading theories about how the galactic bulge formed, so scientists have more work to do puzzling out its secrets. Clocking how fast stars are dancing across the region should help. And astronomers will have a new tool for studying the bulge: the James Webb Space Telescope, due to launch next year, is planning to study these stars as well.