Shockwaves in the ‘cosmic web’ connecting galaxies seen for 1st time
A composite image of 3 previous data-based simulation images, including radio, magnetic fields, and gases. (Image credit: F. Vazza, D. Wittor and J. West)
Scientists have discovered the first evidence of shock waves flowing through the “cosmic web,” a massive network of intertwined threads that represents the largest structure in the universe.
The discovery represents tantalizing evidence of magnetic fields weaving through the gas, dust and dark matter tendons that bind galaxies together.
Scientists first began to think that on the largest scales, the universe is arranged in a web-like pattern with filaments crossing the great voids in space and pulling galaxies into clusters in the 1960s. Two decades later using computer modeling, researchers were able to determine what this large universal network might look like for the first time.
Astronomers have since mapped the cosmic web with actual observations in the process answering questions about its structure. However, one element has remained frustratingly shrouded in mystery: Magnetic fields that may extend throughout the cosmic web.
Related: Faint filaments of ‘Cosmic Web’ stretching across Universe finally found
“Magnetic fields permeate the universe – from planets and stars to the vast spaces between galaxies,” lead author and International Center for Radio Astronomy Research (ICRAR) researcher Tessa Vernstrom said in a statement. (opens in new tab) “However, many aspects of cosmic magnetism are still not fully understood, especially on the scales seen in the cosmic web.”
Vernstrom added that when matter coalesces in the universe, it produces a shock wave that accelerates the particles, and this amplifies the intergalactic magnetic fields. In the cosmic web, gravity pulls filaments together and this should generate shock waves that make the magnetic field in the web stronger. As a result, these fields should emit a radio glow that should be observed by radio telescopes here on Earth.
“These shock waves emit radio emissions that should cause the cosmic web to ‘glow’ in the radio spectrum, but it has never been definitively detected because of how weak the signals are,” Vernstrom continued.
By collecting data and all-sky radio maps from the Global Magneto-Ionic Medium Survey, the Planck Heritage Archive, the Owens Valley Longwave Array, and the Murchison Widefield Array on known clusters and filaments in the cosmic web, Wernstrom and team put re these radio shows for the first time.
A composite image of 3 different observations of the cosmic web (gas, radio and magnetic) accompanied by a composite image. (Image credit: F. Vazza, D. Wittor, and J. West, Composition by K. Brown) Clash of filaments of a cosmic web
Researchers first began searching for signals and a radio glow from the cosmic web in 2020. They detected initial signals from cosmic web shock waves, but could not rule out that these contained emissions from galaxies and celestial objects other than shock waves—otherwise observations of values that were considered “background noise” in this research.
This led them to look for a different type of signal, polarized radio light, which they reasoned would be impaired by less background noise. Polarization occurs when light waves pass through a filter that allows only waves with a specific orientation to exit. After this filtering, the light is polarized.
“Since very few sources emit polarized radio light, our search was less prone to contamination and we were able to provide much stronger evidence that we are seeing emission from shock waves in the largest structures in the universe, which helps to confirm our models for the growth of this large-scale structure,” Vernstrom explained.
By collecting their data, the team ensured that the weak radio wave signal was amplified. This can then be compared to the latest cosmological simulations created with Project Enzo’s hydrodynamic astrophysical calculations. This resulted in the creation of the first simulation of the cosmic web that includes predictions of polarized radio light from cosmic shock waves.
Understanding the magnetic fields triggered in radio waves by these shock waves can now be used to expand and refine our theories of how the universe expands. The results also have the potential to help astronomers solve the mysterious origins of cosmic magnetism.
The team’s research was published in the February 15 edition of the journal Science Advances (opens in new tab).
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