A new series of high-resolution cosmological simulations suggests the Milky Way is situated within a vast, flat sheet of dark matter stretching tens of millions of light-years across, according to research published in Nature Astronomy in January 2026. This structure provides a compelling explanation for why galaxies in the Local Group appear to be receding more slowly than predicted by conventional, spherical mass distribution models. Researchers led by Ewoud Wempe of the Kapteyn Astronomical Institute utilized the Bayesian Origin Reconstruction from Galaxies (BORG) method to test this hypothesis.
Traditional models struggled to align the estimated mass of the Local Group, often cited between 1.3 and 2.3 trillion solar masses, with the observed peculiar velocity field of surrounding galaxies. The new research proposes a flattened mass distribution where the central plane exhibits a density roughly twice the cosmic average, creating voids above and below this midplane. This geometric arrangement fundamentally alters local gravitational dynamics, effectively damping infall velocities toward the Local Group’s center.
The simulations produced 169 realizations of a Local Group analogue, drawing parameters from cosmic microwave background data and the motions of 31 nearby galaxies. The resulting dark matter sheet, extending beyond 10 megaparsecs, aligns closely with the observed Supergalactic Plane, suggesting visible matter traces this underlying, invisible framework. This alignment significantly strengthens the case for a non-spherical mass configuration.
This sheet geometry resolves decades-old mass puzzles that relied on simpler two-body timing arguments involving the Milky Way and Andromeda. While the Local Group itself totals approximately 3.3 ± 0.6 trillion solar masses, the surrounding sheet contributes substantially more gravitational influence in a manner inconsistent with a uniform sphere. The model successfully reproduces the observed “coldness” of the local Hubble flow, where velocities within the plane remain low, below 30 kilometers per second.
Evidence supporting the existence of such structures extends to the early universe, as noted in related reports, including those referencing observations from the Atacama Large Millimeter/submillimeter Array (ALMA). Early massive galaxy systems, such as SPT0311-58 observed when the universe was 780 million years old, were also found embedded in dense, trillion-solar-mass dark matter halos. These observations suggest dark matter sheets may be fundamental to large-scale structure formation across cosmic time.
Despite the strong observational match to velocity data, the current model faces constraints based on tracer galaxy coverage. The 31 galaxies used primarily lie near the Supergalactic plane, limiting direct observation of predicted strong vertical inflows exceeding 100 kilometers per second from the voids above and below the sheet. Testing these vertical dynamics requires identifying more dwarf galaxies at high supergalactic latitudes.
The research team acknowledges boundary conditions within their 40-megaparsec simulation box could influence the inferred alignment directionality. However, the authors maintain that these limitations do not negate the underlying geometry or the successful reconciliation between mass estimates and measured galactic motions. Further high-latitude spectroscopic surveys are crucial for validating the anisotropic gravitational field predicted by this flat dark matter architecture.
