A new map of dark matter in the local universe, developed using machine learning, reveals various filamentous structures undiscovered that connect galaxies.
This cosmic mapping could allow studies on the nature of dark matter, as well as on the history and future of our local universe, according to its authors.
Dark matter is an elusive substance that constitutes 80% of the universe. It also provides the skeleton of what cosmologists call the cosmic web, the large-scale structure of the universe that, due to its gravitational influence, dictates the motion of the galaxies and other cosmic material.
However, currently distribution unknown local dark matter because it cannot be measured directly. Instead, researchers must infer their distribution based on their gravitational influence in other objects in the universe, such as galaxies.
“Ironically, it is easier to study the distribution of dark matter much further away because it reflects a very distant past, which is much less complex, “explains Donghui Jeong, associate professor of astronomy and astrophysics at Penn State University and corresponding author of the study.” Over time, as the large-scale structure of the universe has grown, the complexity of the universe has increased, making it inherently more difficult to measure dark matter locally, “he says.
Previous attempts to map the cosmic web began with a early universe model and then they simulated the evolution of the model over billions of years. However, this method is computationally intensive and has so far not been able to produce results detailed enough to view the local universe.
In the new study, the researchers adopted a completely different approach, using machine learning to build a model that uses information about the distribution and motion of galaxies to predict the distribution of dark matter.
The researchers built and trained their model using a large set of galaxy simulations, called Illustris-TNG, which includes galaxies, gases, other visible matter, and dark matter. The team specifically selected simulated galaxies comparable to the Milky Way and finally identified what properties of galaxies are necessary to predict the distribution of dark matter.
“When given certain information, the model essentially can fill the gaps based on what you’ve looked at before, “said Jeong.” The map in our models doesn’t fit the simulation data perfectly, but we can still reconstruct very detailed structures. We found that including the motion of the galaxies (their peculiar radial velocities) in addition to their distribution dramatically improved the quality of the map and allowed us to see these details. “
The research team then applied their model to real data from the local universe of the Cosmicflow-3 galaxy catalog. The catalog contains comprehensive data on the distribution and motion of more than 17,000 galaxies in the vicinity of the Milky Way, within 200 megaparsecs. The resulting map of the local cosmic web is published in an article that appears in Astrophysical Journal.
The map successively reproduced prominent structures known in the local universe, including the ‘local leaf’, a region of space that contains the Milky Way, nearby galaxies in the ‘local group’ and galaxies in the Virgo cluster, and the ‘local vacuum’– A relatively empty region of space next to the local group. In addition, he identified several new structures that require further investigation, including smaller filamentary structures that connect galaxies.
“Having a local map of the cosmic web opens a new chapter of cosmological study“, dice Jeong it’s a statement. “We can study how the distribution of dark matter relates to other emission data, which will help us understand the nature of dark matter. And we can study these filamentous structures directly, these hidden bridges between galaxies“.
For example, it has been suggested that galaxies Milky Way and Andromeda they may be slowly moving towards each other, but it is unclear if they can collide in many billions of years. Studying the dark matter filaments that connect the two galaxies could provide important information about their future.
“Because dark matter dominates the dynamics of the universe, basically determine our destiny“says Jeong.” So we can ask a computer to develop the map over billions of years to see what will happen in the local universe. And we can evolve the model back in time to understand the history of our cosmic neighborhood, “he adds.
Researchers believe they can improve the accuracy of their map adding more galaxies. Planned astronomical studies, for example, using the James Webb Space Telescope, could allow them to add faint or small galaxies that have not yet been observed and galaxies that are further away.