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Ask Ethan: If Gravity Attracts, How Can The ‘Dipole Repeller’ Push The Milky Way? (Synopsis)

4 Feb 2017, 16:18 UTC
Ask Ethan: If Gravity Attracts, How Can The ‘Dipole Repeller’ Push The Milky Way? (Synopsis)
(200 words excerpt, click title or image to see full post)

“For the first time, astronomers have outlined and named the network of galaxies that includes the Milky Way, adding a line to our cosmic address and further defining our place in the universe.” -Douglas Quenqua
There’s been a longstanding puzzle in astrophysics that’s finally coming to a head. For nearly a century, we’ve known that our Universe is expanding, and that the distance to a galaxy determines its average apparent recessional speed from us. But on top of that is an additional motion — a peculiar velocity — caused by the local gravitational field of the Universe.
A two-dimensional slice of the overdense (red) and underdense (blue/black) regions of the Universe nearby us. Image credit: Cosmic Flows Project/University of Hawaii, via http://www.cpt.univ-mrs.fr/.
When we look at the motion of our own galaxy, we see it’s moving about twice as fast in one direction as the attractive masses would allow. But underdense regions, where there’s less mass and gravity than average, can serve as an effective repeller, failing to attract other matter just as much as overdense regions can attract it. Thanks to a newly mapped and accounted for cosmic void, we might finally understand how our galaxy is moving through ...

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