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Milky Way and Andromeda held together by dark matter sheet
The Milky Way and Andromeda galaxies are trapped in a sheet of dark matter, a new study says.
According to a team of scientists led by the University of Groningen, in the Netherlands, this 32-million-light-year-long sheet of dark matter encases both our home galaxy and the entire nearby Local Group of galaxies.
The scientists said on January 27, 2026, that they used a detailed computer simulation of local gravity conditions to uncover the structure of this sheet. They found that two huge voids sandwich the mass of dark matter. And this structure seems to explain why nearby large galaxies – other than Andromeda – are fleeing the Milky Way, instead of being pulled toward us.
The peer-reviewed journal Nature Astronomy published the findings on January 27, 2026.
Our cosmic neighborhood
When accounting for all the mass in the universe, 85% of it is dark matter, while just 15% of it is normal matter (that which we can see). Dark matter doesn’t reflect light, but it does interact gravitationally with itself and with regular matter and energy. So that means that where it clumps and gathers at high or low densities shapes the underlying geometry of the universe.
The authors argue their computer simulation of gravitational conditions from the Big Bang to the present results in a dark matter distribution that carries almost all other galaxies away from the Local Group. Astronomers call this expansion of the universe the Hubble flow. At the same time, the model shows why the Milky Way and Andromeda galaxies appear to be on a collision course. From the paper:
…The observed quiet local Hubble flow can be consistent with the halo masses implied for Andromeda and the Milky Way … only if the mass distribution is strongly concentrated in a sheet out to at least 10 megaparsecs (32 million light-years), with substantially underdense regions both above and below this Supergalactic Plane.
Edwin Hubble and the expanding universe
In the early 20th century, astronomer Edwin Hubble discovered the Milky Way is just one of many galaxies in the universe. He also found that almost all galaxies are moving away from us. This outward flow was a key clue that the cosmos began with the Big Bang and has been expanding ever since.
However, the Andromeda Galaxy was and remains an exception. It, the Milky Way and the dozens of other smaller members of the Local Group, seemed immune to the force pushing the rest of the cosmos apart. Now a group of European astrophysicists claim to have cracked this mystery. Lead author Ewoud Wempe of the University of Groningen said it’s the first time anyone has attempted such an elaborate computer simulation of the evolving universe. Wempe said:
We are exploring all possible local configurations of the early universe that ultimately could lead to the Local Group. It is great that we now have a model that is consistent with the current cosmological model on the one hand, and with the dynamics of our local environment on the other.
A simulation starting with Cosmic Microwave Background
The computer started its simulation with the early universe. It began with tiny deviations that statistically matched the oldest light we can detect, the Cosmic Microwave Background. The areas chosen for the simulation eventually transformed into galaxy formations that match our local conditions of distance and speed. But these areas also had to move like the Local Group does with respect to more distant galaxies.
The computer found hundreds of matches for the Milky Way-Andromeda system. Inside these areas, a reduced Hubble flow allows and encourages galaxy clusters like the Local Group. Yet outside them – at much larger distances – galaxies rush away, sometimes at speeds exceeding the Hubble flow.
By combining the hundreds of simulations of dark matter distributions resulting in systems matching the Milky Way and Andromeda, the researchers created the best fit for what we actually see around us. The end result is a dark matter environment in the form of a sheet matching the distribution of the galaxies in the Local Group.
Milky Way and Andromeda vs. the universe
In our cosmic neighborhood, the simulations resulted in predictions of dark matter concentrated into a sheet extending well beyond the region of the Local Group. It didn’t stop there. The simulation even showed there must be large low-density regions on either flattened side of the dark matter sheet. These areas do exist and are known as the Local Voids.
The simulation even predicted the flattened distribution of far more distant galaxies in the Local Supercluster without knowing of its existence.
Researchers created a virtual twin of the Local Group that explains how the universe came to look the way it does. Also, they’ve answered a question that’s excited and perplexed astronomers for the better part of a century. As co-author Amina Helmi of the University of Groningen explained:
I am excited to see that, based purely on the motions of galaxies, we can determine a mass distribution that corresponds to the positions of galaxies within and just outside the Local Group.
Bottom line: A new computer simulation shows the Milky Way Galaxy is inside an enormous dark matter sheet. This sheet lies between two voids. The geometry explains our Local Group and why more distant galaxies aren’t pulled in toward us.
Via University of Groningen
Source: The mass distribution in and around the Local Group
Read more: Earth could be in a void, Big Bang sound waves suggest