Optical image of the Abell 3391/95 system captured with a DECam. Overlaying the eROSITA image (darker = higher gas density) and radio lines (yellow) of the ASKAP telescope. Credit: Reiprich et al. , Astronomy and Astrophysics

We owe our existence to a slight deviation. Exactly about 13.8 billion years ago, it was the great explosion Event. It is the beginning of space and time, but it is also the beginning of all the matter that makes up our universe today. Although it was initially concentrated at one point, it expanded by leaps and bounds – a giant gas cloud in which matter is almost uniformly distributed.

Almost, but not quite: In some parts, the cloud was denser than others. It is for this reason alone that planets, stars and galaxies exist today. This is because the denser regions exerted slightly higher gravitational forces, pulling gas from their surroundings towards them. So more and more substances are concentrated in these areas over time. However, the distance between them became empty and more emptied. Over the course of a good 13 billion years, a kind of spongy structure has evolved: large “holes” without any matter, with regions between them where thousands of galaxies congregate in a small space, so-called galactic clusters.

Still image from simulation showing the distribution of hot gas (left), compared to the eROSITA X-ray image of the Abell 3391/95 system (right). Credit: Reiprich et al. , Astronomy and Astrophysics

A fine mesh of gas filaments

If it really happened this way, galaxies and clusters should be connected to each other by gas remnants, like the fine threads of a spider’s web. “According to the calculations, more than half of all baryonic matter in our universe is in these strings – this is what the matter of stars and planets is made of, just as we ourselves,” explains Prof. Dr. Thomas Reprich of the Argylander Institute for Astronomy at the University of Bonn. However, it has so far escaped our eyes: due to the tremendous expansion of the filaments, the material in them is very dilute: it contains only ten particles per cubic meter, which is far less than the best void we can create on Earth.

However, with a new measuring instrument, the eROSITA Space Telescope, Reiprich and his colleagues have now made the gas fully visible for the first time. “EROSITA has detectors that are very sensitive to the type of X-ray radiation that is emitted by the gas in a filament,” explains Ribrich. “It also has a large field of view – like a wide-angle lens, it captures a relatively large portion of the sky in a single size at very high resolution.” This allows for detailed images of massive objects such as strings to be captured in a relatively short time.

In this view of the eROSITA image (right; left again simulated for comparison), very dull areas of the thin gas are also visible. Credit: left: Reiprich et al., Space Science Reviews, 177, 195; Right: Reiprich et al., Astronomy and Astrophysics

Confirm the standard form

In their study, the researchers examined an asteroid called Abell 3391/95. This is a system of three galaxy clusters, about 700 million light-years away from us. The eROSITA images not only show the many individual groups and galaxies but also the gas filaments connecting these structures. The entire filament is 50 million light-years long. But it could be more massive: Scientists assume the images only show a section.

“We compared our observations to the results of the simulations that reconstruct the evolution of the universe,” Ribrich explains. The eROSITA images are strikingly similar to computer-generated graphics. This indicates that the widely accepted standard model for the evolution of the universe is correct. Most importantly, the data show that the missing material may already be hidden in the threads.

Reiprich is also a member of the Interdisciplinary Research Area (TRA) “Building blocks of matter and fundamental interactions” at the University of Bonn. In six different regulatory bodies, scholars from the most diverse faculties and disciplines come together to work collaboratively on research topics relevant to the future at the University of Excellence.

Reference: “The Galactic Cluster System Abell 3391/95. Intergalactic intermediate emission filaments of 15 Mpc, warm gas bridge, conglomerates, and (re) accelerated plasma Detected by combining SRG / eROSITA data with ASKAP / EMU and DECam data ‘by TH Reiprich, A. Veronica, F. Pacaud, ME Ramos-Ceja, N. Ota, J. Sanders, M. Kara, T. Erben, et al. ., Approved, Astronomy and Astrophysics.
DOI: 10.1051 / 0004-6361 / 202039590

Participating institutions and financing:

Nearly 50 scientists from institutions in Germany, the USA, Switzerland, Chile, Australia, Spain, South Africa and Japan participated in the study.

EROSITA was developed with funding from the Max Planck Society and the German Space Center (DLR). The telescope was launched into space last year on board a Russian-German satellite created with support from the Russian space agency Roscosmos. This work also used the Dark Energy Camera (DECam) on the Víctor M. Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory, NSF’s NOIRLab program, and the Australian Pathfinder Array Telescope (ASKAP) built and operated by CSIRO (Organization Commonwealth Scientific and Industrial Research). The current study was funded by several research funding organizations in the participating countries.