Astronomers discover giant cosmic sheet around the Milky Way

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 Astronomers discover giant cosmic sheet around the Milky Way

For decades, astronomers wondered why most nearby galaxies are speeding away from the Milky Way instead of being pulled in by its gravity. New simulations reveal the answer: our galaxy sits in a gigantic, flat sheet of matter surrounded by huge empty voids. This hidden structure—dominated by dark matter—balances gravitational forces and lets neighboring galaxies drift outward. The discovery finally explains the puzzling motions of galaxies just beyond our Local Group.

Simulated movement and speed (indicated by the length of the arrows) of objects surrounding the Local Group (in the centre of the image). Credit: Ewoud Wempe and collaborators

Nearly a century ago, astronomer Edwin Hubble discovered that almost all galaxies are receding from the Milky Way. This observation became a cornerstone of modern cosmology because it provided key evidence that the universe is expanding and that it began with the Big Bang. Even during Hubble's era, however, astronomers knew the pattern was not universal. One notable exception is our neighboring galaxy Andromeda, which is moving toward the Milky Way at roughly 100 kilometers per second.


For about fifty years, scientists have puzzled over another related mystery. Most large galaxies near our own, aside from Andromeda, appear to be moving away from us rather than being pulled inward by gravity. This seems surprising because these galaxies reside near the Local Group (the Milky Way, the Andromeda Galaxy and dozens of smaller galaxies), whose combined mass should exert a noticeable gravitational influence.

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