In a first, scientists record shockwaves in the cosmic web

The cosmic web is the name astronomers give to the structure of our Universe. It refers to the clusters, filaments, dark matter, and voids that make up the basis of this ever-expanding Universe. We can observe this via optical telescopes by mapping the locations of galaxies.

In a new research published in Science Advances, for the first time, scientists claim to have observed shockwaves moving through these galaxy clusters and filaments that make up the galactic or cosmic web. A phenomenon that has long been a universal mystery.

The researchers have recorded radio emissions coming from the shockwaves across the cosmic web – the first observational evidence that accelerating particles, taking the form of these shockwaves, are at work in the Universe.

Dr Tessa Vernstrom, lead author of the research, writes, “In the past, we have only ever observed these radio shockwaves directly from collisions between galaxy clusters. However, we believe they exist around small groups of galaxies, as well as in cosmic filaments.”

The study is led by the International Centre for Radio Astronomy Research (ICRAR) based in Australia, in partnership with Commonwealth Scientific and Industrial Research Organisation (CSIRO) scientists.

Observing these shockwaves is not the easiest thing. For one, the glow emanating from the shockwaves is faint and spread out,  and with galaxies themselves being much brighter, they can hide the radio glow making it challenging to detect it directly. Secondly, the telescopes used for observation create both signal and unwanted noise. The noise is sometimes larger than the radio glow.

So the team of scientists found a way to deal with it, by using a technique called stacking. Dr Vernstrom explains that stacking is when you average together images of many objects too faint to see individually, which decreases the noise, or rather enhances the average signal above the noise.

Although back in 2020, Dr Vernstrom's team had found signals which could be attributed to these cosmic waves, it was difficult to say that these signals were indeed coming from the magnetic fields.

But just the stacking alone wasn’t enough because the radio glow emitted was highly polarized. So the team decided to try the stacking experiment on maps of polarized radio light, which helped them find where the signals were coming from.

They were able to detect the shockwaves that the team was looking for.

Dr Vernstrom says these new observations will help astronomers understand how magnetism works at the largest scales in the Universe.