“The universe resembles a Swiss cheese – but one with huge holes: Large areas in space are absolutely empty. In between, thousands of galaxies crowd in a comparatively small space. These clusters are connected by highways of thin matter gas, like the gossamer filaments of a spider’s web,” reports The University of Bonn about gargantuan filaments in the universe that fueled the formation of clusters of galaxies and galaxies at places where the filaments crossed, creating dense regions of matter –the cheese.
Earlier, 2019 research from the RIKEN Cluster for Pioneering Research and the University of Tokyo suggests that gas falling along massive filaments under the force of gravity in the early universe triggered the formation of starbursting galaxies and supermassive black holes, giving the universe the structure that we see today. In accordance with the predictions of the cold dark matter model of galaxy formation, the filaments are extensive, extending over more than 1 million parsecs–a parsec being just over three light years–and are providing the fuel for intense formation of stars and the growth of supermassive black holes within the proto-cluster.
“It is very exciting to clearly see for the first time multiple and extended filaments in the early universe,” said Michele Fumagalli visiting professor at Durham University about the 2019 research. “We finally have a way to map these structures directly, and to understand in detail their role in regulating the formation of supermassive black holes and galaxies.”
The image at the top of the page is a detailed computer simulation of the complex structure of the cosmic web. Long filaments of dark matter (blue) connect knots of galaxies and galaxy clusters (pink), while gas (orange) permeates throughout. Courtesy of the Illustris Collaboration.
Predicted by the Standard Model–”But Difficult to Prove”
Although this is what the standard model of cosmology predicts, it was hard to prove until recently because the matter in the gas filaments is so diluted that it eluded the view of even the most sensitive measuring instruments: The filaments contain just ten particles per cubic meter, which is far fewer than are present in the best vacuum that Earthbound humans can produce. Even the interstellar medium, the relatively empty space between the stars in our Milky Way Galaxy, contains a million atoms per cubic meter.
A Thread 50 Million Light Years Long
Following the 2020 discovery of an intergalactic thread of gas at least 50 million light-years long, scientists have now developed images with an unprecedented level of detail of the Northern Clump—a cluster of galaxies found on this thread. The unfathomably large thread-like structures of hot gas that surround and connect galaxies and galaxy clusters was observed by astronomers at the University of Bonn. Its structure is uncannily similar to the predictions of recent computer simulations. By combining imagery from various sources including CSIRO’s ASKAP radio telescope, SRG/eROSITA, XMM-Newton and Chandra satellites, and DECam optical data, the scientists could make out a large galaxy at the center of the clump, with a black hole at its center.
“We Owe Our Existence to a Tiny Aberration”
“We owe our existence to a tiny aberration,” reported the University of Bonn in 2020. Over the course of 13 billion years since the Big Bang, “a kind of sponge structure developed consisting of large holes without any matter, with areas in between where thousands of galaxies are gathered in a small space, so-called galaxy clusters, that should still be connected by remnant filaments of the primordial gas, like the gossamer-thin threads of a spider web.”
“According to calculations, more than half of all baryonic matter in our universe is contained in these filaments—this is the form of matter of which stars and planets are composed, as are we ourselves,” explained Dr. Thomas Reiprich from the Argelander Institute for Astronomy at the University of Bonn. “Yet it has so far escaped our gaze: Due to the enormous expansion of the filaments, the matter in them is extremely diluted: It contains just ten particles per cubic meter, which is much less than the best vacuum we can create on Earth.”
In a June 2021 press conference, the eROSITA team at the University of Bonn presented new observations of the clump, which appears to be moving at high speed. Jets of matter are streaming out behind it “like the braids of a running girl,” says lead author of the study, Angie Veronica from the Argelander Institute for Astronomy at the University of Bonn. The image shows the Northern Clump as it appears in X-rays (blue, XMM-Newton satellite), in visual light (green, DECam), and at radio wavelengths (red, ASKAP/EMU).
“The excellent sensitivity of the ASKAP telescope to faint extended radio emission is the key that allows the detection of these jets of radio emission from the supermassive black hole. The shape and orientation of these jets in turn provide important clues to the motion of the galaxy hosting the black hole,” said he leader of the Evolutionary Map of the Universe (EMU) project, Andrew Hopkins at Australian Astronomical Optics, Macquarie University, which contributed data from ASKAP for the study.
Evolutionary Map of the Universe–”Signals from the Dawn of the Universe”
The EMU project uses the new ASKAP telescope to make a census of radio sources in the sky to try to understand how the stars and galaxies were first formed, and how they evolved to their present state, where planets and people are formed. The idea of doing this census is so that we can catch galaxies in all their different stages of evolution, and try to place them in sequence, and so study how their properties change as they evolve. We currently know of about 2.5 million radio sources, and EMU will detect about 70 million. Most of these radio sources will be
galaxies millions of light years away, many containing massive black holes, and some of the signals we detect will have been sent less than half a billion years after the Big Bang, which created the Universe 13.8 billion years ago.
Creation of Large-Scale Structures
In an email to The Daily Galaxy, Andrew Hopkins wrote: “ Our current model of the Universe includes dark matter as well as normal (or baryonic) matter. Simulations looking at how such material evolves over cosmic history provide strong predictions for how it condenses along filaments into the clumps that form galaxies and galaxy clusters. These latest observations, which combine X-ray data from eROSITA with radio data from the ASKAP EMU project, reveal structures remarkably consistent with those predictions.
“This reinforces our understanding of how normal and dark matter jointly work together to form the large scale structures (clusters and filaments of galaxies and gas) we see in the Universe,” continued Hopkins. “At radio wavelengths we can infer the presence of a supermassive black hole due to the outflow of matter, the ‘spillover’ in a sense, from the material falling into it. This shows up as jets of radio emission shooting out from the galaxy’s centre. The emission from such black holes gives us insight into the way black holes populate the Universe, and we know they are intimately connected with the evolution of the galaxies hosting them. Feedback between the formation of new stars in a galaxy and the effects of the outflow from supermassive black holes are an important component in the way galaxies change over cosmic history. It is through projects such as EMU, which in the coming few years will catalogue the largest sample known of such supermassive black holes, that we will gain a deeper understanding of this interplay, and the history and fate of galaxies like our own Milky Way.”
Overall, the observations confirm the theoretical view that the gas filament is an intergalactic road of matter. The Northern Clump is moving along this road at high speed toward two other, much larger galaxy clusters called Abell 3391 and Abell 3395. “It’s sort of falling into these clusters and will continue to enlarge them—just like the principle of ‘winner takes all,'” says Professor Reiprich. “What we’re seeing is a snapshot of that fall.”
The observations agree with the result of the Magneticum computer simulations developed by researchers of the eROSITA consortium. They can therefore also be taken as an argument that the current assumptions about the origin and evolution of the Universe are correct. This includes the view that a large part of matter is invisible to our measuring instruments. Eighty-five percent of our universe is believed to consist of this dark matter. In the standard model of cosmology, it plays an important role as a condensation nucleus that caused gaseous matter to condense into galaxies after the Big Bang.
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