Shockwaves shake the cosmic web

Astronomers have detected huge shockwaves shaking the cosmic web that connects all the galaxies in the universe.
A simulation of the cosmic web showing shockwaves producing radio waves (pink) as they collide with magnetic fields (blue)

The astronomers have detected enormous shockwaves that shake the cosmic web connecting all the galaxies in the universe. This study offers vital clues as to how the largest structure in the cosmos was formed.

Discovery was made by stitching together thousands of images from radio telescopes. Scans revealed the gentle radio glow produced by shockwaves from colliding matter in the largest structures of our universe.

The Cosmic Web

Cosmic web is a gigantic network of celestial superhighways paved with hydrogen gas and dark matter that intertwine with each other. Galaxies tend to form where the most strands of the web intersect. A new study (ref.) published on February 15 in the journal Science provides vital clues about the nature of the mysterious magnetic fields that extend next to these intersections.

“Magnetic fields permeate the universe, from planets and stars to the largest spaces between galaxies” said astronomer and lead author Tessa Vernstrom in a statement. “However, many aspects of cosmic magnetism are not yet fully understood, especially at the scales of the cosmic web” These intersections, formed after the Big Bang, have formed as clusters of matter from the turbulent particle-antiparticle broth of the young universe. The subsequent rapid expansion pushed the filaments outward to form an interconnected structure that surrounds countless voids.

Not completely frozen, the matter of the cosmic web can sometimes collide violently. When this happens, the matter merges, and enormous shockwaves push charged particles that bounce through the magnetic fields of the web, emitting a faint glow. These shockwaves had already been identified around the large galaxy clusters of the universe. But until now, they had never been observed around the web itself.

Shockwaves and radio emissions

“Shockwaves emit radio emissions that make the cosmic web shine in the radio spectrum, but it has never been definitively detected due to the weakness of the signals” Vernstrom said. To detect these weak signals, the researchers used data from the Global Magneto-Ionic Medium Survey, Owens Valley Long Wavelength Array, and Murchison Widefield Array. The three databases were used to stack 612,025 pairs of galaxy clusters together when they were close enough to be directly connected by the web’s intersections. The stacking helped to increase and make visible the weak radio emissions from shockwaves.

Highlighting only the polarized radio waves, the researchers then found the signal they were looking for. “Since very few sources emit polarized radio light, our research was less subject to contamination. We were able to provide compelling evidence for shockwave emissions in the largest structures of the universe. All of this helps to confirm our models for the growth of this large-scale structure” Vernstrom said.

Now that the existence of shockwaves has been confirmed, they could be used to probe the nature of the enormous magnetic fields that pervade the web, which play an unknown role in shaping the universe.

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