### by Veronica Biffi & Klaus Dolag

More than half of the matter in our Universe has so far eluded our view. Astrophysicists have predicted however where it might be: in so-called filaments, unimaginably long structures made of hot gas that surround and connect galaxies and galaxy clusters. These filaments of hot gas in the computer simulations by Dr. Veronica Biffi and PD Dr. Klaus Dolag at the ORIGINS Cluster of Excellence are strikingly similar in their structure to the 50 million light years long filament which has now been observed for the first time by a team led by the University of Bonn using the eROSITA space telescope. While these observations confirm the models of the origin and development of our Universe, the simulations allow an interpretation of the results that recently appeared in the journal Astronomy & Astrophysics, shedding new light on the origin of these structures.

We owe our existence to a tiny irregularity. Almost exactly 13.82 billion years ago, everything started with a "Big Bang": the beginning of space and time, but also of all matter that makes up our Universe today. This was initially concentrated at one point, but expanded at breakneck speed to a gigantic gas cloud in which matter was almost uniformly distributed — almost, but not completely. In some places the cloud was somewhat denser than in others, and this alone is why there are planets, stars and galaxies today: the denser regions exerted somewhat stronger gravitational forces, drawing in the gas from their surroundings. In this way, a complex, large-scale structure started to appear, with more and more matter concentrated in walls, filaments and crossing points, whereas the space in between became emptier and emptier — all in all resembling a sponge. Thus, within the last 13 billion years, the large-scale structure in our Universe developed in a manner whereby galaxies are clustered together in a small space, so-called galaxy clusters, connected by fine, spiderweb-like filamentary structures and large "holes" without matter therein.

### A fine web of gas filaments

If our Universe really evolved in that way, the galaxies and clusters would still be connected by remnants of this gas, like the thin threads of a spiderweb. According to theoretical predictions, this is expected to contain more than half of all baryonic matter. Nevertheless, it has so far escaped our sight due to its extreme diluteness of a mere ten particles per cubic meter — much less than what we can reach with the best vacuum experiment on Earth. Latest observations of Reiprich et al, however, using the eROSITA space telescope, reveal the gas comprehensively for the first time. eROSITA is an x-ray telescope whose detectors are particularly sensitive to the type of x-rays emitted by the gas in cosmic filaments. Its large field of view images a relatively large part of the sky in a single measurement, and at a very high resolution. As a result, detailed images of objects as large as the filaments can be taken in a relatively short time.

Image showing the distribution of hot gas in the output of the Magneticum simulation (left) compared with the eROSITA X-ray image of the Abell 3391/95 system (right); (c) Reiprich et al., Astronomy & Astrophysics, DOI: 10.1051/0004-6361/202039590

### Interpretation and confirmation from cosmological simulations

In their study the scientists examined a celestial object called Abell 3391/95. This is a system of three galaxy clusters which is about 700 million light-years away from us. The eROSITA images reveal 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 and a smaller filament appears to “bridge” the two main portions of the Abell 3391/95 system.

“The new eROSITA images of the observed system resemble remarkably the outcome of our cosmological simulations” explains PD Dr. Dolag. In the Magneticum simulations developed by their group at the University Observatory Munich, Dr. Biffi and PD Dr. Dolag found a very similar pair of galaxy clusters connected by warm gas in a bridge-like filament and surrounded by other objects, aligned in a much wider filamentary structure that spans a region of 15 megaparsecs. The computer simulations confirm that such long filaments contain a substantial amount of diluted gas and extend over large regions of space. "Our simulations also show that other groups and clusters of galaxies move along the filaments, towards the cosmic web knots such as the one where the A3391/95 analog resides", the scientists explain. These studies can uniquely help to interpret the origin of the observed pair and filament, and the particular properties of the gas in them: "the extremely dilute and colder gas in the filament seems to come from very different directions, almost orthogonal, with respect to the hotter gas within the galaxy clusters", explains Dr. Biffi, "and the evolution of its properties over the last ten billion years is also different".

Shown is a 15 megaparsec large region centered on the counterpart of the A3391/95 analog system from the Magneticum simulation. The different lines show how material within the two clusters (red and gold) and the bridge (blue) in between was assembled within the last ten billion years. (c) V. Biffi and K. Dolag (LMU). [click to see an animation of the image]

Highlights

 Pair of galaxy clusters in a wide, warm web of gas Ausgerechnet! Unser Universum Gas perturbations reveal protoplanets The central parsecs of the low-luminosity active galaxy NGC 1052: evidence for a truncated accretion disc Clusters of Small Clumps in High-Redshift Disk Galaxies Magneticum Pathfinder: The evolution of the universe in an unmatched extend The complex Interplay between Spin, Mass, and Morphology in Galaxies Magneticum sheds new light on recently discovered Fast Radio Bursts (FRBs) A Disk-Disk Major Merger Event in a  Cosmological Hydrodynamical Zoom-Simulation The formation of filamentary bundles in turbulent molecular clouds G2 modelled as a mass-losing source of gas Supernova-driven galactic winds The Dark Halo-Spheroid Conspiracy and the Origin of Elliptical Galaxies Phd Award 2012 of the Astronomische Gesellschaft CAST group outing 2012 Evolution of the Galactic Centre Cloud G2 Universe Cluster PhD Thesis Award 2011 Evolution of Molecular Clouds in Spiral Galaxies by Clare Dobbs Globular Clusters Black Hole Correlation by Andreas Burkert Cosmological Resimulations by Ludwig Oser Star Formation in the Galactic Centre by Christian Alig A New Model for the Antennae Galaxies by Simon Karl Simulating the Bullet Cluster by Chiara Mastropietro Triggered Star Formation by Matthias Gritschneder The Mystery of Sedna by Hagen Schulte in den Bäumen The Formation of Fossil Galaxy Groups in the hierarchical Universe by Elena D'Onghia Molecular Cloud Formation in Colliding Flows by Fabian Heitsch Comparison of hydro codes on planet-disk interaction problem by Pawel Ciecielag Orbital Structure of Galaxies in N-Body Simulations by Roland Jesseit

### by Klaus Dolag

What happened after the big bang? How do stars and galaxies originate? What role does dark matter play in this? How does our universe evolve? To bring such outstanding questions to the public, the Klaus Dolag lead a team including man students from CAST and from the USM to develop a new full-dome show, which since 1st of March is shown daily at the Planetarium of the Deutsches Museum. Here the Magneticum Team shows and explain how they have used the supercomputer SuperMUC to create elaborate and spectacular simulations to understand, how our universe is evolving and how galaxies are formed within it.

Highlights

 Pair of galaxy clusters in a wide, warm web of gas Ausgerechnet! Unser Universum Gas perturbations reveal protoplanets The central parsecs of the low-luminosity active galaxy NGC 1052: evidence for a truncated accretion disc Clusters of Small Clumps in High-Redshift Disk Galaxies Magneticum Pathfinder: The evolution of the universe in an unmatched extend The complex Interplay between Spin, Mass, and Morphology in Galaxies Magneticum sheds new light on recently discovered Fast Radio Bursts (FRBs) A Disk-Disk Major Merger Event in a  Cosmological Hydrodynamical Zoom-Simulation The formation of filamentary bundles in turbulent molecular clouds G2 modelled as a mass-losing source of gas Supernova-driven galactic winds The Dark Halo-Spheroid Conspiracy and the Origin of Elliptical Galaxies Phd Award 2012 of the Astronomische Gesellschaft CAST group outing 2012 Evolution of the Galactic Centre Cloud G2 Universe Cluster PhD Thesis Award 2011 Evolution of Molecular Clouds in Spiral Galaxies by Clare Dobbs Globular Clusters Black Hole Correlation by Andreas Burkert Cosmological Resimulations by Ludwig Oser Star Formation in the Galactic Centre by Christian Alig A New Model for the Antennae Galaxies by Simon Karl Simulating the Bullet Cluster by Chiara Mastropietro Triggered Star Formation by Matthias Gritschneder The Mystery of Sedna by Hagen Schulte in den Bäumen The Formation of Fossil Galaxy Groups in the hierarchical Universe by Elena D'Onghia Molecular Cloud Formation in Colliding Flows by Fabian Heitsch Comparison of hydro codes on planet-disk interaction problem by Pawel Ciecielag Orbital Structure of Galaxies in N-Body Simulations by Roland Jesseit

### by Lennart Reb and Klaus Dolag

In a collaboration with the PARSEC group at the Instituto de Astrofísica de Canarias, we investigate the central sub-arcsec region of the low-luminosity active galactic nucleus (LLAGN) NGC 1052, covering 10 orders of magnitude in frequency. This prototypical, nearby LLAGN is an ideal case to shed some light on the internal changes that are predicted in LLAGNs, the most abundant group of AGNs in the Local Universe.

The high-angular resolution data allow us to infer the continuum emission within ~17 pc around the black hole to be not dominated by thermal emission from dust in a torus (grey line, lower plot) as measured in Seyfert 2 AGNs. Instead, the compact jet–disc model representation (black thin line, upper plot) captures the prominent features of the continuum emission.

The individual model components are synchrotron emission (blue dashed line) and synchrotron self Comptonisation (cyan double-dot-dashed line) of the thermalised plasma, synchrotron emission of the accelerated plasma (green dash-dotted line), and the (maximum contribution of a) standard accretion disc (orange dotted line). This jet representation suggests that non-thermal processes dominate the nuclear continuum emission and thus the continuum luminosity.

We further investigate the power balance in the LLAGN NGC 1052, finding that the accretion power of this standard disc, i.e. the power equivalent of the accretion rate, is too low by one order of magnitude to account for the observed continuum luminosity (light blue line, lower plot). However, an optically thick and geometrically thin accretion disc is an integral component of the Unified Model for AGNs, required to feed the subsequent processes.
Any hotter standard accretion disc, i.e. with a higher accretion power, violates the spectral limits of optical/UV measurements (approximated by a power law, dark-green dotted line). We thus introduce a truncated accretion disc and derive a truncation radius to mass-light conversion efficiency relation, which we use to reconcile the inferred accretion power with the continuum luminosity. As a result we find that a truncated disc (red line) providing the necessary accretion power must be truncated at , which is consistent with the inner radius derived from the observations of the Fe K$\alpha$ line in the X-ray spectrum of this nucleus. This is the first time to derive a limit on the truncation radius of the accretion disc from high-angular resolution data only, i.e. evidence for a truncated accretion disc. Therefore it contributes to an ongoing discussion about the physical changes in LLAGNs, advancing our understanding of the participating processes in these objects.

Highlights

 Pair of galaxy clusters in a wide, warm web of gas Ausgerechnet! Unser Universum Gas perturbations reveal protoplanets The central parsecs of the low-luminosity active galaxy NGC 1052: evidence for a truncated accretion disc Clusters of Small Clumps in High-Redshift Disk Galaxies Magneticum Pathfinder: The evolution of the universe in an unmatched extend The complex Interplay between Spin, Mass, and Morphology in Galaxies Magneticum sheds new light on recently discovered Fast Radio Bursts (FRBs) A Disk-Disk Major Merger Event in a  Cosmological Hydrodynamical Zoom-Simulation The formation of filamentary bundles in turbulent molecular clouds G2 modelled as a mass-losing source of gas Supernova-driven galactic winds The Dark Halo-Spheroid Conspiracy and the Origin of Elliptical Galaxies Phd Award 2012 of the Astronomische Gesellschaft CAST group outing 2012 Evolution of the Galactic Centre Cloud G2 Universe Cluster PhD Thesis Award 2011 Evolution of Molecular Clouds in Spiral Galaxies by Clare Dobbs Globular Clusters Black Hole Correlation by Andreas Burkert Cosmological Resimulations by Ludwig Oser Star Formation in the Galactic Centre by Christian Alig A New Model for the Antennae Galaxies by Simon Karl Simulating the Bullet Cluster by Chiara Mastropietro Triggered Star Formation by Matthias Gritschneder The Mystery of Sedna by Hagen Schulte in den Bäumen The Formation of Fossil Galaxy Groups in the hierarchical Universe by Elena D'Onghia Molecular Cloud Formation in Colliding Flows by Fabian Heitsch Comparison of hydro codes on planet-disk interaction problem by Pawel Ciecielag Orbital Structure of Galaxies in N-Body Simulations by Roland Jesseit

### by Til Birnstiel

Astronomers have used a novel technique to reveal the hitherto unsuspected presence of protoplanets in orbit around a young star.

Although more than 3000 fully formed ‘exoplanets’ have now been discovered in mature star systems outside our own, much remains to be learned about how planets evolve. It is now accepted that planets are born in protoplanetary disks filled with gas and dust that are associated with young stars. Unfortunately, the techniques used to find fully formed exoplanets cannot be applied to the detection of young protoplanets in such systems. But now an international team of astronomers, which included LMU physicist Til Birnstiel, has used a new approach that has enabled them to discern the tell-tale signs that the disk which encircles the star HD 163296 hosts two protoplanets. In parallel, a second team has employed a variant of the method to show that the system harbors a third planet. Both papers will appear shortly in Astrophysical Journal Letters.

“A few years ago, the first hints of multiple ring structures were discovered within the gas and dust that make up protoplanetary disks. These faint rings were taken to indicate the presence of young planets,” Birnstiel says. “However, the possibility could not be ruled out that alternative mechanisms were responsible for the formation of these rings,” he adds. Taking advantage of the high resolution attainable in at radio wavelength with the Atacama Large Millimeter/Submillimeter Arrays (ALMA) – an international radiotelescope located high in the Chilean Andes – astronomers have now tackled this issue using a completely new approach. They used ALMA to measure the distribution and the radial velocity of the carbon monoxide gas within the disk around HD 163296, looking for perturbations in gas flow that would signal the presence of protoplanets. The star itself is about four million years old and some 330 light-years from Earth.

Carbon monoxide molecules emit electromagnetic radiation at radio wavelengths, which can be readily detected by ALMA. Subtle changes in the wavelengths of the emission lines resulting from the Doppler shift reveal the radial velocity of the gas. This in turn allowed Birnstiel and his colleagues to infer its rate of rotation of within the disk with high precision, and to search for variations that might be correlated with the presence of planets. The other group was able to measure the actual velocity of the gas flow, which allowed them to probe the outer regions of the disk. “The data show that the radial velocity of the gas varies in exactly the kind of pattern one would expect if its motions were perturbed by three planetary bodies, each with a mass approximately equal to that of Jupiter. This is a very good indication that planets have indeed formed within the disk,” Birnstiel says. “So this method can be employed to find young planets that have escaped our notice up to now.”

Highlights

 Pair of galaxy clusters in a wide, warm web of gas Ausgerechnet! Unser Universum Gas perturbations reveal protoplanets The central parsecs of the low-luminosity active galaxy NGC 1052: evidence for a truncated accretion disc Clusters of Small Clumps in High-Redshift Disk Galaxies Magneticum Pathfinder: The evolution of the universe in an unmatched extend The complex Interplay between Spin, Mass, and Morphology in Galaxies Magneticum sheds new light on recently discovered Fast Radio Bursts (FRBs) A Disk-Disk Major Merger Event in a  Cosmological Hydrodynamical Zoom-Simulation The formation of filamentary bundles in turbulent molecular clouds G2 modelled as a mass-losing source of gas Supernova-driven galactic winds The Dark Halo-Spheroid Conspiracy and the Origin of Elliptical Galaxies Phd Award 2012 of the Astronomische Gesellschaft CAST group outing 2012 Evolution of the Galactic Centre Cloud G2 Universe Cluster PhD Thesis Award 2011 Evolution of Molecular Clouds in Spiral Galaxies by Clare Dobbs Globular Clusters Black Hole Correlation by Andreas Burkert Cosmological Resimulations by Ludwig Oser Star Formation in the Galactic Centre by Christian Alig A New Model for the Antennae Galaxies by Simon Karl Simulating the Bullet Cluster by Chiara Mastropietro Triggered Star Formation by Matthias Gritschneder The Mystery of Sedna by Hagen Schulte in den Bäumen The Formation of Fossil Galaxy Groups in the hierarchical Universe by Elena D'Onghia Molecular Cloud Formation in Colliding Flows by Fabian Heitsch Comparison of hydro codes on planet-disk interaction problem by Pawel Ciecielag Orbital Structure of Galaxies in N-Body Simulations by Roland Jesseit

### by K. Dolag & A. Ragagnin

In close collaboration with the Excellence Cluster Universe and the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences, we now initiated "Cosmowebportal". This unique data centre for cosmological simulations provides access to the results of the world's most extensive set of cosmological hydrodynamic simulations, Magneticum Pathfinder. The complete simulations are saved at the LRZ in Garching on a data store for large datasets, which is connected to the supercomputer SuperMUC. Using a web interface, interested scientists can, for example, select objects from the raw simulation data, process it and even create virtual observations mimicking existing or future space telescopes.

Visualizations of the simulated distributions of gas and stars in the Universe from data provided by Cosmowebportal: The cube represents a space section of the Universe (more than 300 million light years), the bright spots on the cube faces show galaxies and galaxy clusters along the cosmic web. The first two disks zoom into the central galaxy cluster, the third disk (far right) demonstrates how an observation of the zoom area would look with an X-ray telescope ("virtual telescope"). Image Credits: P. Baintner und H. Brüchle (LRZ)

# Showcase

Further information:

Press release: Excellence Cluster Universe
http://c2papcosmosim.lrz.de/
www.magneticum.org

Original publication:
Ragagnin et al.: „A web portal for hydrodynamical, cosmological simulations”,
Astronomy and Computing, Vol. 20, July 2017; online 6 June 2017

Highlights

 Pair of galaxy clusters in a wide, warm web of gas Ausgerechnet! Unser Universum Gas perturbations reveal protoplanets The central parsecs of the low-luminosity active galaxy NGC 1052: evidence for a truncated accretion disc Clusters of Small Clumps in High-Redshift Disk Galaxies Magneticum Pathfinder: The evolution of the universe in an unmatched extend The complex Interplay between Spin, Mass, and Morphology in Galaxies Magneticum sheds new light on recently discovered Fast Radio Bursts (FRBs) A Disk-Disk Major Merger Event in a  Cosmological Hydrodynamical Zoom-Simulation The formation of filamentary bundles in turbulent molecular clouds G2 modelled as a mass-losing source of gas Supernova-driven galactic winds The Dark Halo-Spheroid Conspiracy and the Origin of Elliptical Galaxies Phd Award 2012 of the Astronomische Gesellschaft CAST group outing 2012 Evolution of the Galactic Centre Cloud G2 Universe Cluster PhD Thesis Award 2011 Evolution of Molecular Clouds in Spiral Galaxies by Clare Dobbs Globular Clusters Black Hole Correlation by Andreas Burkert Cosmological Resimulations by Ludwig Oser Star Formation in the Galactic Centre by Christian Alig A New Model for the Antennae Galaxies by Simon Karl Simulating the Bullet Cluster by Chiara Mastropietro Triggered Star Formation by Matthias Gritschneder The Mystery of Sedna by Hagen Schulte in den Bäumen The Formation of Fossil Galaxy Groups in the hierarchical Universe by Elena D'Onghia Molecular Cloud Formation in Colliding Flows by Fabian Heitsch Comparison of hydro codes on planet-disk interaction problem by Pawel Ciecielag Orbital Structure of Galaxies in N-Body Simulations by Roland Jesseit