Nearly a century ago, astronomer Edwin Hubble discovered that nearly all galaxies are receding from the Milky Way. This statement became a cornerstone of contemporary cosmology since it provided key evidence that the universe is expanding and that it began with the Big Bang. Even during Hubble’s era, nevertheless, astronomers knew the pattern was not universal. One notable exception is our neighboring galaxy Andromeda, which is moving toward the Milky Way at roughly 100 kilometers per second.
For about fifty years, scientists have puzzled over one other related mystery. Most large galaxies near our own, except for Andromeda, look like moving away from us reasonably than being pulled inward by gravity. This seems surprising because these galaxies reside near the Local Group (the Milky Way, the Andromeda Galaxy and dozens of smaller galaxies), whose combined mass should exert a noticeable gravitational influence.
A Giant Cosmic Sheet Across the Local Group
A world research team led by PhD graduate Ewoud Wempe of the Kapteyn Institute in Groningen believes it has found the reason. Using advanced computer simulations, the researchers discovered that the matter surrounding the Local Group is arranged in a broad, flattened structure that stretches tens of hundreds of thousands of light-years across. This structure includes not only unusual matter but in addition the invisible dark matter that surrounds galaxies. Above and below this flattened region lie enormous empty areas generally known as cosmic voids.
The simulations show that this arrangement of matter can accurately reproduce each the positions and speeds of the galaxies observed around us. In other words, the pc model successfully recreates the identical patterns astronomers see in the true universe.
Making a Virtual Twin of Our Cosmic Neighborhood
To construct their model, the scientists began with conditions from the early universe. They used measurements of the cosmic microwave background to estimate how matter was distributed shortly after the Big Bang. A strong computer then evolved this early universe forward in time, eventually producing a system that matches the current day Local Group.
The resulting simulations replicate the masses, locations, and motions of the Milky Way and Andromeda, in addition to the positions and velocities of 31 galaxies just outside the Local Group. Since the model so closely resembles our surroundings, researchers describe it as a “virtual twin” of our cosmic environment.
When the model includes the flat distribution of matter, the encompassing galaxies move away from us at speeds much like those actually observed. Despite the gravitational pull of the Local Group, galaxies throughout the plane are influenced by additional mass spread throughout that very same plane. This distant mass counterbalances the Local Group’s gravity. Meanwhile, regions outside the plane contain only a few galaxies, which explains why we don’t see objects falling toward us from those directions.
A Longstanding Puzzle Finally Explained
In line with lead researcher Ewoud Wempe, the study represents the primary detailed try and determine the distribution and motion of dark matter in the realm across the Milky Way and Andromeda. “We’re exploring all possible local configurations of the early universe that ultimately may lead to the Local Group. It’s great that we now have a model that’s consistent with the present cosmological model on the one hand, and with the dynamics of our local environment on the opposite.”
Astronomer Amina Helmi also welcomed the findings, noting that the issue has challenged researchers for many years. “I’m excited to see that, based purely on the motions of galaxies, we are able to determine a mass distribution that corresponds to the positions of galaxies inside and just outside the Local Group.”