The cosmic velocity web – University of Hawaiʻi System News

The cosmic velocity web is represented by surfaces of knots in red and surfaces of filaments in grey. Credit: Daniel Pomarede, Yehuda Hoffman, R. Brent Tully and Helene Courtois.

The cosmic web—the distribution of matter on the largest scales in the universe—has usually been defined through the distribution of galaxies. Now, a new study published in The Astrophysical Journal, by a team of astronomers from France, Israel and Hawaiʻi demonstrates a novel approach. Instead of using galaxy positions, they mapped the motions of thousands of galaxies. Because galaxies are pulled toward gravitational attractors and move away from empty regions, these motions allowed the team to locate the denser matter in clusters and filaments and the absence of matter in regions called voids.

Matter was distributed almost homogeneously in the very early universe, with only miniscule variations in density. Over the 14 billion year history of the universe, gravity has been acting to pull matter together in some places and leave other places more and more empty. Today, the matter forms a network of knots and connecting filaments referred to as the cosmic web. Most of this matter is in a mysterious form, the so-called “dark matter.” Galaxies have formed at the highest concentrations of matter and act as lighthouses illuminating the underlying cosmic structure.

The newly defined cosmic velocity web defines the structure of the universe from velocity information alone. In those regions with abundant observations, the structure of the velocity web and the web inferred from the locations of the galaxy lighthouses are similar. This agreement provides strong confirmation of the fundamental idea that structure developed from the growth of initially tiny fluctuations through gravitational attraction.

Brent Tully

The cosmic velocity web analysis was led by Daniel Pomarede, Atomic Energy Center, France, with the collaboration of Helene Courtois at the University of Lyon, France; Yehuda…

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