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Andromeda’s Vast Halo Offers Clues about Galactic Evolution

2 Sep 2020, 16:00 UTC
Andromeda’s Vast Halo Offers Clues about Galactic Evolution
(200 words excerpt, click title or image to see full post)

Wait long enough — something like 4.5 billion years — and we’ll have a huge elliptical galaxy resulting from the merger of our own Milky Way with Andromeda (M31). I’ve always been fascinated with Andromeda because being the nearest large galaxy, and a fine spiral at that, it gives us a look at how our own galaxy must appear from the outside. Its faintness to the naked eye belies its size, an object considerably larger than the Moon from our perspective, though best seen, of course, on a Moonless night. And now we learn it is even bigger than we thought.
The Absorption Map of Ionized Gas in Andromeda (Project AMIGA) is the source for this information. A new study coming out of this program uses Hubble data to map the vast gas envelope surrounding Andromeda, a diffuse halo of plasma extending 1.3 million light years from the galaxy and in some directions, as far as 2 million light years. To put this into perspective, Andromeda itself is 2.5 million light years away, meaning that our two galaxies may already be encountering each other as their two haloes nudge up against each other.
Now the reference to the Moon gives ...

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