From Ethan Siegel: “The Stars Of Andromeda, Inside And Out, As Revealed By Hubble”

From Ethan Siegel

Andromeda Galaxy Adam Evans
Andromeda Galaxy Adam Evans

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.

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A Mosaic of the 117 million resolved stars — plus many more unresolved ones — in the disk of the Andromeda galaxy. Image credit: NASA, ESA, J. Dalcanton, B.F. Williams, L.C. Johnson (University of Washington), the PHAT team, and R. Gendler.

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.

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Closeup of a large region of the Andromeda galaxy’s disk, containing hundreds of open star clusters (identifiable as bright blue sparkles). Image credit: NASA, ESA, J. Dalcanton, B.F. Williams, L.C. Johnson (University of Washington), the PHAT team, and R. Gendler.

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Six of the most spectacular star clusters in Andromeda. The brilliant red star in the fifth image is actually a foreground star in the Milky Way. Over a thousand new clusters were found in this survey. Image Credit: NASA, ESA, and Z. Levay (STScI); Science Credit: NASA, ESA, J. Dalcanton, B.F. Williams, L.C. Johnson (University of Washington), and the PHAT team.

Far outside of the center, in the outer disk and the faint galactic halo, a different set of populations thrive.

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Image credit: NASA, ESA and T.M. Brown (STScI), of the stars in Andromeda’s outer disc.

The outer disc of Andromeda (above) shows a wide variety of stars, including many Sun-like ones and older variables.

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Image credit: NASA, ESA and T.M. Brown (STScI), of the stars in Andromeda’s giant stellar stream. The Milky Way’s foreground stars are clearly identified by their diffraction spikes.

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.

See the full article here .

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“Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan