A Cosmic Web Connecting the Universe Shapes Dark Matter In Galaxies, Study Finds
An anonymous reader quotes a report from Motherboard: Our universe is connected by a cosmic web made of giant threads of dark matter and gas that stretch across millions of light years and intersect at "nodes" populated by dense clusters of galaxies. This vast network shapes the distribution and evolution of galaxies in fundamental ways that scientists are trying to unravel with ever-sharper observations and advanced simulations. Now, a team led by Callum Donnan, a postgraduate student in astronomy at the University of Edinburgh, have identified a key correlation between the chemical makeup of galaxies and their location within the cosmic web. Using both real-life observations and computer simulations, the team found that "galaxies closer to nodes [display] higher chemical enrichment than those farther away," a discovery that reveals some of the mysterious dynamics that link the universe, according to a study published on Monday in Nature Astronomy. To home in on this question, Donnan and his colleagues examined galaxies within about a billion light years of the Milky Way observed by the Sloan Digital Sky Survey in New Mexico, which covers a huge area of the sky. The team studied the elemental makeup of gasses in the interstellar spaces within these real-life galaxies, a property that is known as gas-phase metallicity. The results revealed that galaxies close to the nodes of the cosmic web were richer in "metals," which in astronomy refers to any element heavier than helium. A weaker correlation was also observed with proximity to the web's filaments, which are the threads that stretch across the universe and link nodes together. The team ran sophisticated cosmological simulations using the IllustrisTNG platform, which supported the observational findings. Significantly, the approach revealed that a galaxy's position in the cosmic web modulates its chemical content even when other factors, such as the density of a particular region in the universe, are taken into account. Naturally, that raises the question of why galaxies located near nodes are enriched with more metals compared to those distributed along filaments or in empty "voids" within the cosmic web. Donnan's team isolated two major drivers of this relationship: The absorption of gas from outside of galaxies and the evolution of stars and dark matter inside of them. Galaxies feed on gasses that are strewn across space in the intergalactic medium, but those that are further from nodes consume much more of this outside material than those close to nodes. Since intergalactic gas is metal-poor, it dilutes the enriched gas of far-flung galaxies, lowering their overall gas-phase metallicities. Galaxies near nodes don't consume as much of this metal-poor material, which helps to keep them chemically enriched with higher concentrations of heavier elements. In addition, galaxies close to nodes seem to have matured earlier than those located at a distance. These galaxies had a head-start in birthing new stars and collecting dark matter, which is a mysterious substance that makes up most of the matter in the universe.
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