Discovery of a massive cosmic sheet explains the unusual motion of galaxies surrounding the Milky Way

University of Groningen researchers discover a massive flat sheet of dark matter surrounding the Milky Way, explaining the mysterious motion of nearby galaxies.

By: AXL Media

Published: Mar 6, 2026, 6:22 AM EST

Source: The information in this article was sourced from University of Groningen

The Mystery of Receding Neighbors

Since Edwin Hubble’s landmark observations nearly a century ago, it has been understood that the universe is expanding and most galaxies are moving away from the Milky Way. However, a local anomaly has puzzled scientists for fifty years: while the Andromeda galaxy is famously being pulled toward us at 100 kilometers per second, most other large galaxies just outside our Local Group are receding. Given the combined mass of the Milky Way and Andromeda, gravity should theoretically be pulling these neighbors inward. This unexplained outward drift suggested a missing piece in our understanding of the local cosmic architecture.

Simulating a Virtual Twin of the Universe

A research team led by Ewoud Wempe of the Kapteyn Institute used advanced computer simulations to create a "virtual twin" of our cosmic neighborhood. By inputting data from the cosmic microwave background—measurements of the universe shortly after the Big Bang—the team evolved the model forward in time to the present day. The resulting simulation perfectly replicated the masses and locations of the Milky Way and Andromeda, as well as the specific positions and velocities of 31 galaxies situated just beyond the Local Group's boundaries.

The Role of the Cosmic Sheet and Voids

The simulations revealed that the Local Group is not isolated but is instead embedded within a gigantic, flattened structure of matter stretching tens of millions of light-years across. This cosmic sheet consists of both visible and invisible dark matter. Crucially, the regions directly above and below this plane are occupied by enormous "cosmic voids"—vast areas essentially empty of matter. This specific arrangement of mass provides the missing gravitational context; the matter distributed throughout the flat sheet exerts an outward pull that counterbalances the local gravity of the Milky Way and Andromeda, allowing neighboring galaxies to drift away.