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Bulked-up neighbor makes the Milky Way a galactic wimp

The galaxy next door, Andromeda, is twice as massive as our own Milky Way galaxy, a new paper published online today in the Monthly Notices of the Royal Astronomical Society concludes. Astronomers have long known that Andromeda is bigger and brighter than the Milky Way, but some studies have suggested that our galaxy packs in enough extra invisible dark matter to beat it in total bulk. Now, calculations based on the latest measurements of galactic distances and motions show that each galaxy contains the same proportion of dark matter—about 90%—and that Andromeda is top dog after all.

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