Scientists Discover the Milky Way Is Floating on a Vast Sheet of Dark Matter Stretching Millions of Light-Years

A series of high-resolution simulations has revealed a striking new perspective on the Milky Way’s position in the cosmos. Far from floating in a symmetrical halo, the galaxy appears embedded in a massive, flat structure composed almost entirely of dark matter.

The finding reframes a decades-long mystery: why nearby galaxies are receding more slowly than expected, given the Local Group’s estimated mass. Traditional spherical models have struggled to reconcile this with observations, leaving a persistent mismatch between theory and motion.

Researchers now point to a dark matter sheet, tens of millions of light-years across, as the underlying force influencing these anomalies. This structure not only matches the observed velocity field but also aligns with large-scale formations seen in the distribution of galaxies around the Milky Way.

Published in Nature Astronomy in January 2026, the study uses observational data and cosmological simulations to propose a flattened mass distribution that challenges conventional assumptions about the galaxy’s surroundings.

Simulations Uncover a Hidden Architecture Around the Milky Way

The project, led by Ewoud Wempe of the Kapteyn Astronomical Institute, utilized the Bayesian Origin Reconstruction from Galaxies (BORG) method to simulate the Milky Way’s environment. The team produced 169 distinct realizations of a Local Group analogue using parameters drawn from cosmic microwave background data and the motions of 31 nearby galaxies.

Results revealed a sheet-like dark matter structure extending beyond 10 megaparsecs, or roughly 30 million light-years. Its central plane contains a density roughly twice the cosmic average, with almost empty voids above and below. This flattened mass alters local gravitational dynamics in ways that reproduce the peculiar velocity field observed around the Milky Way.

The structure affects how gravitational pull is distributed across space. In this configuration, mass at greater distances within the same plane contributes outward forces, effectively damping infall velocities toward the Local Group’s center. This would explain why galaxies in the region exhibit smoother, more stable motions than expected under a spherical mass model.

Visualizations of the simulation showed the dark matter sheet aligned closely with the Supergalactic Plane, an observed structure defined by luminous galaxies. The match between inferred mass and known galactic positions supports the hypothesis that visible matter loosely traces the larger, invisible framework of dark matter.

Decades-Old Mass Puzzles Find a New Solution in Dark Matter Geometry

Historically, astronomers relied on the timing argument to estimate the Local Group’s mass, modeling the Milky Way and Andromeda (M31) as a two-body system formed at the Big Bang. These estimates, first published in 1959, consistently produced values that conflicted with galaxy motion data in the surrounding area.

Efforts to expand the model to include neighboring galaxies still treated mass distribution as spherical. These methods typically yielded upper mass limits between 1.3 and 2.3 trillion solar masses for the Local Group. Yet such figures couldn’t explain the slow recession speeds of galaxies just outside the group’s boundaries.

The sheet model resolves this issue. The new simulations indicate that the Local Group has a combined mass of 3.3 ± 0.6 trillion solar masses, but this is only part of the total gravitational influence. The larger sheet contains over four times more mass within 4 megaparsecs. A spherical model containing that much mass fails to match observed galaxy velocities, but the sheet model aligns with both motion and mass estimates.

The predicted motion within this structure is also more consistent with measurements. Simulations show that velocities within the plane remain low, often below 30 kilometers per second, mirroring the observed “coldness” of the local Hubble flow. Above and below the plane, velocities increase as galaxies move toward the denser midplane, forming a highly anisotropic field.

Echoes of the Dark Matter Sheet Appear in the Early Universe

The idea of dark matter sheets is not limited to the Local Group. Observations using the Atacama Large Millimeter/submillimeter Array (ALMA) have identified massive galaxies forming inside dark matter-dense regions during the early universe. In 2017, researchers reported the discovery of SPT0311-58, a pair of galaxies observed when the universe was just 780 million years old.

These galaxies were embedded in a dark matter halo with an estimated mass of several trillion suns. Their rapid formation rates and dense environments suggest that sheet-like structures of dark matter may be a common feature in galaxy formation across cosmic time.

The similarities support the idea that flattened dark matter configurations play a critical role not only in current galactic motion but also in shaping the early universe’s large-scale structure. Observations of these early systems add weight to the model proposed for the Local Group, reinforcing its potential as a broader cosmological feature.

Additional early-universe modeling and star formation data appear in Phys.org’s report, which contextualizes ALMA’s findings within the larger narrative of dark matter’s role in cosmic evolution.

Proving the Sheet Through Observation

Although the simulations closely match known data, the model is limited by current observational coverage. Most of the 31 galaxy tracers used lie near the plane of the Supergalactic coordinate system, reducing visibility into vertical inflow dynamics from the surrounding voids.

The study anticipates strong inflows from above and below the dark matter sheet, with peculiar velocities exceeding 100 kilometers per second. However, this prediction remains untested due to the lack of high-latitude observations within 5 megaparsecs. Identifying more isolated dwarf galaxies at high supergalactic latitudes could provide critical validation.

The simulations themselves are constrained to a 40-megaparsec box, using periodic boundary conditions that may affect large-scale structure alignment. The researchers note that while this could influence the directionality of the inferred plane, it does not alter the underlying geometry or the match to velocity data.