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If you could view our galaxy from afar, you’d see a beautiful cosmic pinwheel, with most of its light coming from a flat spiral-shaped disk in which the Sun and Earth reside.
A “halo” of ancient stars surrounds the disk. Although it’s much fainter than the disk, the halo houses the oldest stars in the Milky Way. These stars formed when the galaxy itself did, so they can provide unique insight into its birth soon after the Big Bang.
The halo penetrates the disk, so some halo stars are passing close to the Sun. One of the nearest is visible through binoculars on spring evenings, south of the Big Dipper. It’s known as Groombridge 1830, and it’s one of our closer stellar neighbors, at a distance of just 30 light-years. Like the Sun, it’s a main-sequence star, which means it generates energy by fusing together hydrogen atoms to make helium.
Astronomers recently measured the exact diameter of the star. They took aim at the star with an interferometer - an array of telescopes that produces sharp views of stars. They found that Groombridge 1830 is almost exactly two-thirds the diameter of the Sun. They also determined the star’s surface temperature.
Knowing precise properties for nearby halo stars such as Groombridge 1830 means astronomers can use them as templates for halo stars throughout the galaxy - even those that are thousands of light-years away - offering new insights into our home galaxy’s birth and early evolution.
Script by Damond Benningfield, Copyright 2013
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