How the bulge, disk, and halo stars of Andromeda reveal lessons we cannot see about our own galaxy.
“He who would search for pearls must dive below.” –John Dryden
The Milky Way’s plane obscures our view of most stars in our own galaxy, but an even grander spiral — Andromeda — lies 2.5 million light years away.
Even at this modest distance, incredible telescope and camera technology is needed to resolve individual stars in a galaxy beyond our own.
The Hubble Space Telescope recently completed the Panchromatic Hubble Andromeda Treasury, mapping a third of Andromeda’s disk and resolving over 117 million individual stars.
The most metal-rich stars are found near the central bulge, with the newest, bluest stars found in the open clusters.
Far outside of the center, in the outer disk and the faint galactic halo, a different set of populations thrive.
The outer disc of Andromeda (above) shows a wide variety of stars, including many Sun-like ones and older variables.
The stars from the giant stellar stream are also densely packed, obscuring the Universe beyond.
While the diffuse halo’s low-density regions contain many of the oldest, least evolved stars.
They’re lower in heavy elements than any stars found in the disk,
with galaxies up to billions of light years away visible through the gaps in the halo stars.
Mostly Mute Monday tells the story of a single astronomical phenomenon or object in visuals, images and video in no more than 200 words.
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