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Birth of a Supercluster

22 Oct 2018, 16:37 UTC
Birth of a Supercluster ESO/L. Calçada & Olga Cucciati et al.

We have somewhere between 200 billion and 300 billion stars in our galaxy (the number is flexible enough that you’ll see a wide range in the literature). Relate that to the Local Group, the gathering of galaxies that includes both the Milky Way and M31, the Andromeda Galaxy. These are the two most massive members of the Local Group, but depending on how we count dwarf galaxies, it contains more than 30 members spread out over a diameter of 10 million light years. Both the Milky Way and M31 have their own dwarf galaxies.

Then consider the concept of a ‘supercluster,’ which contains galaxy groups within it. Thus the Milky Way is considered part of both the Local Group as well as the Laniakea Supercluster, which is itself home to approximately 100,000 galaxies and subsumes the Virgo Supercluster. The Laniakea Supercluster emerged in the literature in 2014 in a paper examining the relative velocity of galaxies. Laniakea is a Hawaiian word meaning ‘immense heaven.’ R. Brent Tully (University of Hawaii at Manoa) and team identified this structure some 520 million light years in diameter, containing 100,000 galaxies, with a mass of one hundred million billion Suns.

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