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.

Nearly a century ago, Edwin Hubble discovered that almost all galaxies are receding from the Milky Way, providing key evidence that the universe is expanding. But one mystery persisted: most large galaxies near our own, aside from Andromeda, appear to be moving away from us rather than being pulled inward by gravity. This seemed surprising because these galaxies reside near the Local Group, whose combined mass should exert a noticeable gravitational influence.

An international research team led by Ewoud Wempe of the Kapteyn Institute at the University of Groningen used advanced computer simulations to find the explanation. The researchers discovered that matter surrounding the Local Group is arranged in a broad, flattened structure stretching tens of millions of light-years across. This structure includes both ordinary matter and invisible dark matter. Above and below this flattened region lie enormous cosmic voids.

"Because the model so closely resembles our surroundings, researchers describe it as a 'virtual twin' of our cosmic environment," according to the research. When the model includes the flat distribution of matter, the surrounding galaxies move away from us at speeds similar to those actually observed. Despite the gravitational pull of the Local Group, galaxies within the plane are influenced by additional mass spread throughout that same plane, counterbalancing the Local Group's gravity.

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