Optical image of the Abell 3391/95 system taken with the DECam camera. The eROSITA image (darker = higher gas density) and radio contour (yellow) of the ASKAP telescope are placed on top of each other. Credit: Reiprich et al., Astronomy & Astrophysics
More than half of the matter in our universe has so far remained hidden from us. Astrophysicists, however, had a sense of where it might be: in so-called filaments, unfathomable large wire-like structures of hot gas that envelop and connect galaxies and galaxies. A team led by the University of Bonn has now observed for the first time a gas filament 50 million light-years long. Its structure is strikingly similar to the predictions of computer simulations. The observation therefore also confirms our ideas about the origin and evolution of our universe. The results are published in the journal Astronomy & Astrophysics.
Our existence owes us to a small deviation. Almost exactly 13.8 billion years ago, the Big explosion took place. It is the beginning of space and time, but also of all matter that forms our universe today. Although initially concentrated at one stage, it expanded at an incredible rate – a giant gas cloud in which matter was almost uniformly distributed.
Almost, but not completely: in some parts the cloud was a little denser than in others. And for this reason alone, there are planets, stars and galaxies today. This is because the denser areas exerted slightly higher gravitational forces, which attracted the gas from their environment to them. Thus, over time, more and more matter was concentrated in these regions. However, the space between them became increasingly empty. Over the course of a good 13 billion years, a kind of sponge structure has developed: large “holes” without any matter, with areas in between where thousands of galaxies are collected in a small space, so-called galaxies.
Still image of a 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 & Astrophysics
Fine web of gas wires
If this really happened, the galaxies and clusters would still need to be connected by remnants of this gas, such as the gossamer-thin wires of a spider. “According to calculations, more than half of all baronic matter in our universe is contained in these filaments – it is the form of matter that stars and planets consist of, just like ourselves,” explains prof. Dr. Thomas Reiprich from the Argelander Institute of Astronomy at the University of Bonn. Yet it has escaped our gaze so far: Due to the enormous expansion of the filaments, the matter in it is extremely diluted: it contains only ten particles per cubic meter, which is much less than the best vacuum we can create on earth.
However, with a new measuring instrument, the eROSITA space telescope, Reiprich and his colleagues were now able to make the gas completely visible for the first time. “EROSITA has very sensitive detectors for the type of X-rays emitted from the gas in filaments,” Reiprich explains. “It also has a large field of view – like a wide-angle lens, it captures a relatively large part of the air in one measurement and with a very high resolution.” It allows detailed images of large objects such as filaments to be taken in a relatively short time.
In this view of the eROSITA image (right; left again a simulation for comparison) the very faint parts of thin gas are also visible. Credit: left: Reiprich et al., Space Science Reviews, 177, 195; regs: Reiprich et al., Astronomy & Astrophysics
Confirmation of the standard model
In their study, the researchers examined a celestial object called Abell 3391/95. It is a system of three galaxies, which is about 700 million light-years from us. The eROSITA images show not only the clusters and numerous individual galaxies, but also the gas filaments that connect these structures. The entire filament is 50 million light-years long. But it can be even more enormous: the scientists assume that the images show only a part.
“We compared our observations with the results of a simulation that reconstructs the evolution of the universe,” Reiprich explains. ‘The eROSITA images are strikingly similar to computer-generated graphics. This indicates that the generally accepted standard model for the evolution of the universe is correct. The most important thing is that the data show that the missing case was probably hidden in the filaments.
Reiprich is also a member of the Transdisciplinary Research Area (TRA) ‘Building Blocks of Matter and Fundamental Interactions’ at the University of Bonn. In six different TRAs, scientists from the most diverse faculties and disciplines come together to collaborate on future relevant research topics from the University of Excellence.
Reference: “The galaxy cluster system Abell 3391/95. A 15 Mpc intergalactic medium-emission filament, a hot gas bridge, stumps falling, and (again) accelerating plasma discovered 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. ., Accept, Astronomy & Astrophysics.
DOI: 10.1051 / 0004-6361 / 202039590
Participating institutions and funding:
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 Air and Space Center (DLR). The telescope was launched into space last year aboard a Russian-German satellite, the construction of which was supported by the Russian space agency Roskosmos. This work also has the Dark Energy Camera (DECam) on the Víctor M. Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, a program of NSF’s NOIRLab, and the Australian Square Kilometer Array Pathfinder (ASKAP) telescope used, built and managed by CSIRO (Scientific and Industrial Research Organization of the Commonwealth). The current study was funded by several research funding organizations in the participating countries.