New dark matter map
The local universe dark matter map was developed by an international team of scientists, including an astrophysicist from the University of Pennsylvania, USA, using machine learning.
The new map could aid research on the nature of dark matter as well as the history and future of the local universe, which refers to the region of space called the Local Group, housing over 54 galaxies, with the two largest being the Milky Way and the Andromeda galaxy.
Dark matter makes up 80% of the universe, providing the framework for what astrophysicists call the cosmic web, the large-scale structure of the universe, influenced by gravitational forces, determining the motion of galaxies and other cosmic matter.
However, the distribution of local dark matter remains poorly understood, as dark matter cannot be directly measured. Instead, researchers must infer the distribution of dark matter based on its gravitational influence on other cosmic objects, such as galaxies.
Previous efforts to map the cosmic web started with a primitive universe model and then simulated the evolution of this model over billions of years. This method is computationally intensive and has not yet produced detailed enough results to observe the local universe.
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An international research team has created a map of dark matter in the local universe, featuring galaxies (black dots), known cosmic structures (red), and smaller filamentary points (yellow) acting as hidden bridges between galaxies. The X symbol represents the Milky Way, and the arrows indicate the motion of the local universe due to gravitational forces. Image: University of Pennsylvania.
In the new study, scientists took an entirely different approach, using machine learning to construct a model using information on the distribution and motion of galaxies to predict the distribution of dark matter.
The researchers built and trained the new model with a large set of galaxy simulations called Illustris-TNG, which includes galaxies, gas, visible cosmic matter, and dark matter.
The research team specifically selected galaxy simulations that could be compared to the Milky Way and ultimately determined which characteristics of galaxies were necessary to predict the distribution of dark matter.
They then applied the model to real local universe data from the Cosmicflow-3 galaxy catalog. The catalog contains comprehensive data on the distribution and motion of over 17 thousand galaxies in the vicinity of the Milky Way – within 200 megaparsecs.
The local cosmic web map was published in a paper released online on May 26, 2021, in The Astrophysical Journal.
The map continuously reconstructs prominent structures already known in the local universe, including the “local sheet” – the region of space containing the Milky Way, neighboring galaxies in the Local Group, and galaxies in the Virgo cluster, as well as the “local void” – a vast, empty region adjacent to the Local Group.
Additionally, the map identifies some newly discovered structures that require further study, including smaller filamentary structures connecting galaxies.
A New Chapter for Cosmic Research
“A local map of the cosmic web will usher in a new chapter of cosmic research. We can investigate how the distribution of dark matter relates to other emission data, which will help us understand the nature of dark matter. And we can directly study these filamentary structures, the hidden bridges between galaxies,” said Donghui Jeong, an assistant professor of astronomy and astrophysics at the University of Pennsylvania, and a participating researcher.
For instance, there are speculations about the Milky Way and the Andromeda galaxy moving towards each other, but whether a collision will occur in billions of years is still unclear. Researching the dark matter filaments connecting these two galaxies provides crucial insights into their future.
The researchers believe that they can enhance the accuracy of their map by adding more galaxies. Upcoming astronomical surveys, like the James Webb Space Telescope, are expected to enable astronomers to incorporate smaller or fainter galaxies that have never been observed, as well as galaxies farther away, into the map.