Mapping the local cosmic web

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UNIVERSITY PARK, Pa .– A new map of dark matter in the local universe reveals several previously unknown filamentary structures connecting galaxies. The map, developed using machine learning by an international team including a Penn State astrophysicist, could enable studies into the nature of dark matter as well as the history and future of our local universe.

Dark matter is an elusive substance that makes up 80% of the universe. It also provides the backbone for what cosmologists call the “cosmic lattice,” the large-scale structure of the universe which, due to its gravitational influence, dictates the movement of galaxies and other cosmic material. However, the distribution of local dark matter is currently unknown as it cannot be measured directly. Instead, researchers must deduce its distribution based on its gravitational influence on other objects in the universe, such as galaxies.

“Ironically, it’s easier to study the distribution of dark matter much further because it reflects a very distant past, which is much less complex,” said Donghui Jeong, associate professor of astronomy and astrophysics at Penn. State and corresponding study author. “Over time, as the large-scale structure of the universe has developed, the complexity of the universe has increased, so it is inherently more difficult to make measurements on dark matter locally.”

Previous attempts to map the cosmic web started with a model of the early universe, then simulated the model’s evolution over billions of years. However, this method is computationally intensive and so far has not been able to produce results detailed enough to see the local universe. In the new study, the researchers took 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, as well as dark matter. The team specifically selected simulated galaxies comparable to those in the Milky Way and ultimately identified the properties of the galaxies needed to predict the distribution of dark matter.

“When given certain information, the model can basically fill in the gaps based on what he looked at before,” Jeong said. “The map of our models does not match the simulation data perfectly, but we can still reconstruct very detailed structures. We found that including the motion of galaxies – their particular 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 local universe data from the Cosmicflow-3 galaxy catalog. The catalog contains comprehensive data on the distribution and motion of over 17,000 galaxies near the Milky Way – within a radius of 200 megaparsecs. The resulting map of the local Cosmic Web is published in an article that appeared online May 26 in the Astrophysical Journal.

The map has successively reproduced important structures known in the local universe, including the “local leaf” – a region of space containing the Milky Way, neighboring galaxies of the “local group” and galaxies of the cluster. the Virgin – and the “local void” – a relatively empty region of space next to the local group. Additionally, he identified several new structures that require further research, including smaller filamentous structures that connect galaxies.

“Having a local map of the cosmic web opens up a new chapter in cosmological study,” Jeong said. “We can study the relationship between the distribution of dark matter and other emission data, which will help us understand the nature of dark matter. And we can directly study these filamentous structures, these hidden bridges between galaxies.

For example, it has been suggested that the Milky Way and Andromeda galaxies could slowly move towards each other, but it is not known if they could collide in billions of years. Studying the dark matter filaments connecting the two galaxies could provide important information about their future.

“Because dark matter dominates the dynamics of the universe, it fundamentally determines our fate,” Jeong said. “So we can ask a computer to evolve the map for billions of years to see what will happen in the local universe. And we can change the model over time to understand the history of our cosmic neighborhood.

Researchers believe they can improve the accuracy of their map by adding more galaxies. Planned astronomical surveys, for example using the James Web Space Telescope, could allow them to add faint or small galaxies that have not yet been observed and galaxies more distant.

In addition to Jeong, the research team includes Sungwook Hong at the Institute for Astronomy and Space Science at Seoul University / Korea in Korea, Ho Seong Hwang at Seoul National University in Korea, and Juhan Kim at the Korea Institute for Advanced Studies. This research was funded in part by the National Research Foundation of Korea funded by the Korean Ministry of Education, the Korean Ministry of Science, the US National Science Foundation, the Astrophysics Theory program of the US National Aeronautics and Space Administration and the Center for Advanced Computation. at the Korea Institute for Advanced Studies.

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