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Astronomers spot shock waves stirring the web of the universe for the first time

TechScienceAstronomers spot shock waves stirring the web of the universe for the first time
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For the first time, astronomers have caught a glimpse of ripples rippling along the strands of the cosmic web – the vast tangle of galaxies, gas and dark matter that fills the observable universe.

combining hundreds of thousands of radio telescope images The faint glow is detected due to the sending of charged particles by the shock waves. Fly through the magnetic fields that run along the cosmic web. Researchers report on February 17 that observing these shock waves could give astronomers a better look at these large-scale magnetic fields, whose properties and origins are largely mysterious. science advance,

Finally, astronomers “can confirm what has so far only been predicted by simulations – that these shock waves exist,” says astrophysicist Markus Brüggen of the University of Hamburg in Germany, who was not involved in the new study. “

At its largest scale, our universe resembles Swiss cheese. Galaxies are not distributed evenly through space, but tend to cluster together in huge clusters linked by ropey filaments not separated from the dilute gas, galaxies and dark matter and by vastly empty voids (Sn: 10/3/19,

Pulled by gravity, galaxy clusters merge, filaments collide, and gas from the voids falls onto the filaments and clusters. In simulations of the cosmic web, all that action sets off massive shock waves in and out of the continuous filaments.

filaments make up most of the cosmic web but much harder to spot than galaxies ,Sn: 1/20/14, While scientists have observed shock waves around galaxy clusters before, shocks in filaments “have never really been observed,” says astronomer Renaut van Veeren of Leiden University in the Netherlands, who was not involved in the study. “But they should basically be around the cosmic web.”

The shock waves around the fibers will accelerate the charged particles magnetic field in the cosmic web ,Sn: 6/6/19, When this happens, the particles emit light at wavelengths that radio telescopes can detect – although the signals are too weak.

Simulations of the cosmic web and its magnetic field (cyan), as illustrated here, predict that shockwaves along the filaments and around galaxy clusters should emit weak radio signals (pink). The inset shows what a composite of several radio images of galaxy cluster pairs in the simulated web might look like, with colors representing gas temperature and density (higher values ​​are yellow, lower values ​​are purple and black).F Vazza, D Vitor and J West

A shock wave in a filament “would look like nothing, it would look like noise,” says radio astronomer Tessa Wernstrom of the International Center for Radio Astronomy Research in Crawley, Australia.

Instead of looking for individual shock waves, Wernstrom and his colleagues combined radio images of more than 600,000 pairs of galaxy clusters that were close enough to be connected by filaments to create a “stacked” image. This amplified the weak signals and revealed that, on average, there is a faint radio glow from the fibers between the bunches.

“When you can dig beneath the noise and still actually get a result—for me, that’s personally exciting,” Wernstrom says.

The faint signal is highly polarized, meaning that the radio waves mostly align with each other. Highly polarized light is unusual in the universe, but it is expected from radio light cast by shock waves, van Veeren says. “So this is actually, I think, pretty good evidence for the fact that aftershocks really do exist.”

In this computer simulation, gas falling onto the cosmic web (blue) heats up and expands, setting off shockwaves that travel through the hot, expanding gas (red) and the vast network of galaxy clusters and filaments that fill our universe gets rippled. These shockwaves interact with magnetic fields (green) in the cosmic web to produce radio signals that astronomers can observe.

The finding goes beyond confirming the predictions of the cosmic web simulations. Polarized radio emission also provides a rare glimpse into the magnetic fields that permeate the cosmic web, albeit indirectly.

“These shocks,” Bruggen says, “are really able to show that there are large-scale magnetic fields that form [something] Like a wrap around these fibers.

He, van Veeren and Wernstrom all note that it is still an open question as to how cosmic magnetic fields originated in the first place. Equally mysterious is the role these fields play in shaping the cosmic web.

“It’s one of the four fundamental forces of nature, isn’t it? Magnetism,” says Wernstrom. “But at least on such a large scale, we don’t really know how important it is.”

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