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Relying on the deepest visible-light images ever taken in space, astronomers using NASA's Hubble Space Telescope have reliably measured the age of the spherical halo of stars surrounding our neighboring Andromeda galaxy (M31). Approximately one-third of the stars in Andromeda's halo formed only 6 to 8 billion years ago, about half the 11-to-13 billion-year age of the stars in the Milky Way's halo.
Image courtesy of Space Telescope Science Institute. |
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