Astronomers map motion in galaxies spanning hundreds of millions of light-years

A group of scientists comprised of astronomers from the Leibniz Institute for Astrophysics Potsdam (AIP), with help from scientists in China and Estonia, have mapped the motion of galaxies via huge filaments that connect the cosmic web. Researchers have found that these long tendrils of galaxies spin on a scale spending hundreds of millions of light-years. The rotation is said to be on enormous scales never before seen.

Cosmic filaments are massive bridges made of galaxies and dark matter that connect clusters of galaxies. The filaments funnel galaxies towards and into large clusters that sit at the end of the filaments. These filaments are described as a type of cosmic superhighway, and astronomers have mapped the motion of galaxies in those filaments using the Sloan Digital Sky survey.

The Sloan Digital Sky survey is a survey of hundreds of thousands of galaxies. Using Sloan data, scientists were able to determine a new and interesting property of the filaments; that property is that the filaments spin. According to astronomer Peng Wang, despite being thin cylinders similar to pencils that span hundreds of millions of light-years, the filaments are only a few million light-years in diameter.

The massive tendrils of matter rotate and have such massive scale that the galaxies inside them are like specks of dust. The tendrils move like a helix or in corkscrew-like orbits circling around the middle of the filament while traveling along it. Spins of this type have never been seen on such massive scales, and the implication is that there must be an unknown physical mechanism responsible for creating torque on these objects.

Exactly how the angular momentum responsible for the rotation is generated is one of the key unsolved mysteries of cosmology. According to the standard model of structure formation, small overdensities in the early universe grew via gravitational instability as matter flowed from under to overdense regions. This type of potential flow is irrotational or curl-free. Researchers say there is no primordial rotation in the early universe.

That means any rotation present in the universe must be generated as structures form. Cosmic webs in general and filaments specifically are intimately connected with galaxy formation and evolution. These filaments also have a significant impact on galaxy spin, often regulating the direction of how galaxies and their associated dark matter halos rotate. However, the astronomers admit it's unknown if the current understanding of structure formation predicts the filaments themselves should spin.