On the largest scales, matter in the universe is arranged in a cosmic web, which consists of gas filaments separated by cavities, with clusters in which the filaments meet. Photo credits: MAGNETICUM simulation with the kind permission of Klaus Dolag, University Observatory Munich, Ludwig Maximilians University Munich
On the largest scale, the universe consists of a “cosmic web” of huge, thin filaments of gas that stretch between huge clumps of matter. Or that’s what our best models suggest. All we have seen so far with our telescopes are the stars and galaxies in the clumps of matter.
So is the cosmic web real or an invention of our models? Can we confirm our models by directly detecting these weak gaseous filaments?
Until recently, these filaments were elusive. But now a collaboration between Australian radio astronomers and German X-ray astronomers has discovered one.
The newly completed ASKAP (Australian Square Kilometer Array Pathfinder) telescope from CSIRO in Western Australia begins to create a large format image of the universe in radio frequencies. This telescope can see deeper than any other radio telescope and bring new discoveries like the unexplained Odd Radio Circles or ORCs.
Vision with radio waves and X-rays
In this year the first observations of the German eROSITA space telescope were published, which provide us with our deepest large-scale image of the universe in X-ray frequencies. Both next-generation telescopes have an unprecedented ability to scan large areas of the sky at the same time, making them superbly coordinated to study the large-scale features of the universe. Together they can achieve a lot more than either alone, so of course we joined forces.
The first result of this collaboration is the discovery of a cosmic hot gas thread. This study was led by Thomas Reiprich from the University of Bonn and Marcus Brueggen from the University of Hamburg and included Australian researchers from CSIRO and from the Universities of Curtin, Macquarie, Monash and Western Sydney. It is published today in two articles in the journal Astronomy and Astrophysics.
The seven cameras of the eROSITA space telescope enable the imaging of X-rays from large areas of the sky. Photo credit: Max Planck Institute for Extraterrestrial Physics
The cosmic web
The Big Bang 13.8 billion years ago produced a universe filled with invisible dark matter, along with a strange gas of hydrogen and helium and little else. For the next few billion years, the gas clumped under the pull of gravity, forming filaments of matter with huge empty voids between them. The filaments probably contain more than half the matter in the universe, although the filaments themselves only contain ten particles per cubic meter – less than the best vacuum we can create on Earth.
It is believed that almost all of the galaxies we see today, including our own Milky Way, formed in these filaments. We believe that galaxies then slide along the filaments until they fall into the dense galaxy clusters that are clumped together at junctions where filaments meet.
But so far it was all hypothetical – we could see the galaxies and clusters, but we couldn’t see the gaseous filaments themselves. Now eROSITA has directly detected the hot gas in a 50 million light-year long filament. This is an important step forward in confirming that our cosmic web model is correct.
The eROSITA image shows the clusters in the center and the dark green gaseous filament that extends 50 million light years from bottom left to top right. Photo credit: Thomas Reiprich
This picture from a simulation called Magneticum shows clumps moving along the filaments and merging with the main systems to form larger, denser, and hotter structures. Photo credit: Thomas Reiprich
Large-scale development of the analogue A3391 / 95 found in the Magneticum simulation. The gas density distribution is shown in a cubic cutout area of 20 Mpc / h per side around the redshift of the main system in the following coordinates from redshift z ~ 1 to z ~ 0.07. We find that the clumps fall along the large area filaments and merge with the main systems to form larger, denser and hotter structures. Photo credit: Reiprich et al., Astronomy & Astrophysics
A smooth ride
We also expected the hot gas to kick up electrons to create high frequency emissions, but strangely enough we don’t recognize the filament with ASKAP. This tells us that the hot gas flows smoothly without the turbulence that electrons would accelerate to create radio waves. So the galaxies run smoothly when they fall into the clusters.
In ASKAP’s radio images, we can see the individual galaxies falling into the clusters. At radio wavelengths, we often see galaxies surrounded by two jets caused by electrons spurting out from near the black hole in the center of the galaxy.
ASKAP radio data (white) overlay the eROSITA x-ray image (color). The circles show individual radio galaxies. The normally straight jets of the radio galaxies are bent into distorted shapes by the intergalactic winds within the clusters. Photo credit: Marcus Brueggen
However, in our radio images of these clusters, we can see that the jets are bent and distorted when hit by intergalactic winds in the dense gas in the clusters. This is also a good confirmation of our models.
This work is not only important as a confirmation of our model of the universe, but also the first result of the collaboration between ASKAP and eROSITA. These two telescopes are wonderfully coordinated to survey our universe and see the universe as it has never been seen before, and I expect this discovery to be the first of many.
Further information: Radio observations of the merging galaxy cluster system Abell 3391-Abell 3395, arXiv: 2012.08775 [astro-ph.HE] arxiv.org/abs/2012.08775
The Abell 3391/95 galaxy cluster system: A 15 Mpc intergalactic medium emission filament, a warm gas bridge, clumps of infalling matter and (re) accelerated plasma discovered by combining SRG / eROSITA data with ASKAP / EMU and DECam data. 2012.08491 [astro-ph.CO] arxiv.org/abs/2012.08491
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Quote: A thread of the cosmic web: Astronomers discover a 50 million light year long galactic filament (2020, December 18), released on December 21, 2020 from https://sciencex.com/news/2020-12-thread-cosmic-web -astronomers was retrieved -million.html
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