At its largest scale, the Universe is made up of a “cosmic web” made up of giant filaments, a gaseous gas stretched between huge lumps of matter. Or so our best models suggest. All we have seen so far with our telescopes are only the stars and galaxies in the nostrils of matter.
So is the cosmic web real, or a picture of our models? Can we validate our models by directly detecting these weak gaseous filaments?
Until recently, these filaments were incapable. But now a collaboration between Australian radio astronauts and German X-ray astronauts has found one.
The recently completed Australian Pathfinder Array (ASKAP) Telescope at CSIRO is beginning to project a large image of the Universe in radio frequencies. This telescope can see deeper than any other radio telescope, making new discoveries, such as the Odd Radio Circles or ORCs.
Visual with radio waves and X-rays
Also this year the first observations were published by the German eROSITA Space Telescope, which gives us the deepest big picture of the Universe in X-ray frequencies. These two next-generation telescopes have an unparalleled ability to scan large areas of space at the same time, so they are beautifully matched to study the Earth’s vast features. Together, they can achieve much more than on their own, so naturally we have come together.
The first result of this collaboration is the discovery of a cosmic filament of hot gas. This study was led by Thomas Reiprich of the University of Bonn and Marcus Brueggen of the University of Hamburg, and involved Australian scientists from CSIRO and the universities of Curtin, Macquarie, Monash and Western Sydney. It is published today in two papers in the journal Astronomy and Astronomy.
The cosmic web
The Big Bang 13.8 billion years ago brought a Universe full of invisible dark matter, along with the inert gas of hydrogen and helium, and very little else. Over the few billion years, the gas accumulated under gravity attraction, forming filaments of matter with large void gaps between them. The filaments probably account for more than half of the matter in the Universe, even though the filaments themselves are only ten particles per cubic meter – less than the best white we can created on Earth.
Almost every galaxy we see today, including our own Milky way, is thought to have been formed in these filaments. We imagine that galaxies then slide down the filaments until they fall into the dense clusters of galaxies gathered together at junctions where filaments meet.
But so far, this has all been hypothetical – we would see the galleries and the collections, but we would not see the gaseous filaments themselves. Now, eROSITA has discovered the hot gas directly in a 50 million year light filament. This is an important step forward, confirming that our model of the cosmic net is correct.
We also expected the hot gas to vibrate electrons to produce radio frequency transmissions, but strangely, we could not detect the filament with ASKAP. This tells us that the hot gas flows smoothly, without the turmoil that would accelerate electricity to make radio waves. So the galleries get a smooth ride as they fall into the collections.
We see the individual galleries falling into the collections in the radio images from ASKAP. At radio waves, we often see galaxies broken by a pair of jets, caused by electricity scrubbing out from near the black hole in the center of the constellation.
However, in our radio images of these collections, we see the jets bent and moved as if there were intergalactic winds in the dense gas in the collections. Again, this is a good test of our models.
This work is not only important as a test of our model of the Universe, but it is also the first result of the collaboration between ASKAP and eROSITA. These two telescopes are beautifully matched to explore our Universe, seeing the Universe as never seen before, and I think this discovery is the first of many.
Radio views of the unified galaxy collection system Abell 3391-Abell 3395, arXiv: 2012.08775 [astro-ph.HE] arxiv.org/abs/2012.08775
Abell 3391/95 galaxy collection system: 15 Mpc medium diffusion filament, warm gas bridge, infalling material lumps, and (re-) accelerated plasma detected by combining SRG / eROSITA data with ASKAP / EMU and DECam data, arXiv: 2012.08491 [astro-ph.CO] arxiv.org/abs/2012.08491
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