Astronomers have discovered more than 200 distant variable stars known as RR Lyrae stars in the Milky Way's stellar halo. The most distant of these stars is more than a million light years from Earth, almost half the distance to our neighboring galaxy, Andromeda, which is about 2.5 million light years away.
"The halo is the hardest part to study because the outer limits are so far away," GuhaThakurta said."The stars are very sparse compared to the high stellar densities of the disk and the bulge, but the halo is dominated by dark matter and actually contains most of the mass of the galaxy."
The findings are based on data from the Next Generation Virgo Cluster Survey , a program using the Canada-France-Hawaii Telescope to study a cluster of galaxies well beyond the Milky Way. The survey was not designed to detect RR Lyrae stars, so the researchers had to dig them out of the dataset. The Virgo Cluster is a large cluster of galaxies that includes the giant elliptical galaxy M87.
"The way their brightness varies looks like an EKG—they're like the heartbeats of the galaxy—so the brightness goes up quickly and comes down slowly, and the cycle repeats perfectly with this very characteristic shape," GuhaThakurta said."In addition, if you measure their average brightness, it is the same from star to star. This combination is fantastic for studying the structure of the galaxy.
France Dernières Nouvelles, France Actualités
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