Andromeda galaxy's halo, astronomers stared into the galaxy giant with the new Advanced Camera for Surveys through the Hubble Space Telescope. The resulting exposure of over three days, shown above, is the longest exposure in visible light ever taken, although shorter than the multi-wavelength effort toward the Hubble Deep Field. The final image illuminated not only Andromeda (M31) but the distant universe. Andromeda's halo stars turned out to be have a wider range of ages than our Milky Way's halo stars, likely indicating more encounters with small neighboring galaxies. Visible on the above left is one of Andromeda's globular star clusters, while literally thousands of background galaxies are seen in the distance universe, far beyond M31.
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Based on Astronomy Picture Of the Day
Publications with keywords: M 31 - deep field
Publications with words: M 31 - deep field