ASTROPHYSICS

This project targets various central questions in modern astrophysics, including "What is the nature of dark matter?", "How do galaxies form and evolve?" and "Do we understand the extremes of the universe?". Dwarf galaxies provide a natural laboratory for confronting these questions as we will explain below. The formation of dwarf galaxies tracks an extreme situation in various ways. Dwarf galaxies are assumed to be the very first type of galaxy to form in the earliest Universe.

The aim of this project is to create a highly accurate cosmological, hydrodynamical simulation model that can produce extremely realistic representations of dwarf galaxies right into the centers, where dark matter models can be tested.

Numerical sciences are experiencing a renaissance thanks to the spread of heterogeneous computing. The SYCL open standard unlocks GPGPUs, accelerators, multicore and vector CPUs, and advanced compiler features and technologies (LLVM, JIT), while offering intuitive C++ APIs for work-sharing and scheduling. The project allowed for the kick-off of DPEcho (short for Data-Parallel ECHO), a SYCL+MPI porting of the General-Relativity-Magneto-Hydrodynamic (GRMHD) OpenMP+MPI code ECHO, used to model instabilities, turbulence, propagation of waves, stellar winds and magnetospheres, and astrophysical processes around Black Holes, in Cartesian or any coded GR metric.

Currently, the DRESDYN experiment is under construction. It aims to find and understand the mechanisms behind the excitation of a magnetic field due to the precessing motion of a conducting fluid. Such a precessing fluid is, for example, inside the core of the Earth, which is believed to sustain the Earth's magnetic field. To study the flow fields as well as the magnetic fields and to predict optimal parameter regimes for the DRESDYN experiment, numerical simulations are performed on JUWELS CPU using the code SpecDyn.

High-mass star formation is a highly complex and dynamic process involving a large number of physical mechanisms. To better interpret real-world star-forming regions, simulations of collapsing clouds are used. These simulations produce the distribution of matter within star-forming regions, taking into account the effects of gravitational contraction as well as the feedback from massive stars. These simulations are then used to compute synthetic telescope images which may be compared to observations made with instruments like the Atacama Large Millimeter Array (ALMA).

Near field cosmology is the theoretical and observational study of our neighbourhood in the universe. This is the main topic of focus for the CLUES collaboration (www.clues-project.org). Our neighbourhood is the best observed part of the universe where also tiny dwarf galaxies can be studied. The properties of these dwarfs reflect their early formation history and state of the universe at the Cosmic Dawn, when the first stars and galaxies formed. Studying them sheds new light on these times, known as Cosmic Dawn and Epoch of Reionisation.

In project CHMU14, challenging three-dimensional simulations of thermonuclear explosions of white dwarf stars near the Chandrasekhar-mass limit were conducted. These were followed by radiative transfer simulations that allow to predict observables. A comparison with astronomical data shows that such models can explain the subclass of Type Iax supernovae.

Supersonic, magnetised turbulence is ubiquitous in the interstellar medium of galaxies. Unlike incompressible turbulence, supersonic turbulence is not scale-free. The scale that marks the transition from supersonic to subsonic turbulence is the so-called sonic scale, which in the context of star formation may define the critical value for which regions inside of molecular gas clouds collapse under their own gravity to form stars.

A team of researchers led by Dr. Denis Wittor at the University of Hamburg has been leveraging the high-performance power of the JUWELS supercomputer at the Jülich Supercomputing Centre (JSC) for deeper insight into radio relics, cloud of diffuse radio wave emission, often found in galaxy clusters.

Researchers at the Ludwigs-Maximillians Universität München are focused on studying the concentration of galaxies called the Coma, which is made up of more than 1,000 galaxies in our interstellar neighborhood. Using experimental facilities and world-class computng, the team was able to simulate the Coma cluster in unprecedented detail.

Our Cosmic Home, which is the local volume of the Universe centered on us, contains very prominently visible structures, extending over almost one billion light-years. Such structures, ranging from the Local Group over the Local Void and the most prominent galaxy clusters like Virgo, Perseus, Coma and many more, represent a formidable site where extremely detailed observations exist. Therefore, cosmological simulations of the formation of galaxies and galaxy clusters within the Local Universe, rather than any other, randomly selected part of the cosmic web, are perfect tools to test our formation and evolution theories of galaxies and galaxy clusters down to the details. However, at these detailed levels, such simulations are facing various…

Gravitational wave detectors such as LIGO, VIRGO, and KAGRA, have brought about an era of multi-messenger astronomy that has given new insights into the merger of binary compact objects. In all cases, the ability to constrain the characteristics of the compact objects is very limited, especially in the absence of an electro-magnetic (EM) counterpart. Gravitational wave events such as GW190425, however, present a very unique opportunity to study the mass gap regime where the binary could consist of either a black hole and a neutron star (BHNS) or a highly asymmetric neutron star binary (BNS).

The amazing progress in observational cosmology over the last decades has brought many surprises. Perhaps the most stunning is that we live in a Universe where most of the matter (~85%) is comprised of yet unidentified collisionless dark matter particles, while ordinary baryons produced in the Big Bang make up only a subdominant part (~15%). The real physical nature of dark energy, as well as the mass of the neutrinos which contribute a tiny admixture of “hot” dark matter, are profound and fundamental open questions in physics. To make further progress, this firmly established standard cosmological model will be subjected to precision tests in the coming years that are far more sensitive than anything done thus far.

This ongoing project aims at investigating the long-term evolution of a merging binary system of two neutron stars. The investigation conducted within this project is well aligned with the past research conducted by the Relastro group in Frankfurt and is motivated by the gravitational-wave detection GW170817 and its electromagnetic counterpart, the
so-called kilonova. This kilonova signal is produced by the nuclear processes within the dense and neutron rich mass that is ejected during the merger. Since a lot of mass is ejected during the longterm postmerger evolution, it is crucial to investigate this part via state-of-the-art simulations in order to fully understand the observation.

Researchers investigated the formation and evolution of molecular clouds, i.e. the nurseries of star formation, by means of 3D magneto-hydrodynamical simulations. These molecular clouds, which are embedded in a galactic disk like our Milky Way, were modelled with a high spatial resolution using a smart zoom-in approach relying on the adaptive mesh refinement technique. As the modelled molecular clouds were embedded in a realistic astrophysical environment, it was possible to study their detailed evolution, e.g. the impact of supernova explosions and radiation from nearby massive stars. Moreover, the research team modelled the chemical evolution of these clouds as well as their dynamics and complex internal structure.

Before the first stars formed more than 13 billion years ago, the gas of the Universe consisted of hydrogen, helium, and lithium only. Elements necessary for life, eg carbon or oxygen, are produced by stars, and it is of fundamental importance to understand how the first stars formed. With a large allocation on SuperMUC and SuperMUC-NG, state-of-the-art numerical simulations were performed to mimic these first star formation regions. In these high-resolution simulations, two effects – a so-called Lyman-Werner background and streaming velocities – that delay star formation globally were included. It could be demonstrated for the first time that the combination of both effects results in an even more delayed formation of the first stars.

To understand solar and stellar magnetic field evolution combining local and global numerical modelling with long-term observations is a challenging task: even with state-of-the-art computational methods and resources, the stellar parameter regime remains unattainable. Our goal is to relax some approximations, in order to simulate more realistic systems, and try to connect the results with theoretical predictions and state-of-the-art observations. Higher resolution runs undertaken in this project will bring us into an even more turbulent regime, in which we will be able to study, for the first time, the interaction of small- and large-scale dynamos in a quantitative way.

MPIA scientists have developed a planetesimal formation model based on high-resolution hydro-dynamical simulations performed on JSC HPC systems. The simulations were used to model disk turbulence and its two effects on the dust, the mixing and diffusion of the dust on large scales but also the concentration of dust on small scales. This research helped to better understand the efficiency of these processes and to derive initial mass functions for planetesimals and gas giant planets to predict when and where planetesimals and Jupiter-like planets should form and of which size they will be. This is a fundamental step forward in understanding the formation of our own solar system as well as of the many planetary systems around other stars.

The outer layers of the Sun are convectively unstable such that heat and momentum are transported by material motions. These motions are thought to be responsible for the large-scale magnetism and differential rotation of the Sun. Employing a more realistic description of the heat conductivity in our simulations than in previous studies, we demonstrate that stellar convection is highly non-local. Furthermore, we found substantial formally stably stratified but fully mixed layers that can cover up to 40 per cent of the solar convection zone. These results are reshaping our picture of stellar convection.

The hot and dilute astrophysical plasmas - from Solar to galactic scales - are inherently turbulent. The turbulence determines transport and structure formation in accretion disks, in the interstellar medium, in clusters of galaxies as well as their observable radiation. Due to its routing in microscopic kinetic processes the turbulence of astrophysical plasmas is, however, not well understood, yet. Utilizing state-of-the-art microphysics particle-in-cell codes in this project self-consistent 3D electromagnetic kinetic simulations were performed to simulate the kinetic turbulence inherently linked with two fundamental processes of energy conversion in the Universe – collisionless shock waves and magnetic reconnection.

Core-collapse supernovae are among the most energetic events in the Universe and can be as bright as a galaxy. They mark the violent, explosive death of massive stars, whose iron cores collapse to the most exotic compact objects known as neutron stars and black holes. In this project self-consistent 3D simulations with state-of-the-art microphysics were performed for the explosion of a ~19 solar-mass star, whose final 7 minutes of convective oxygen-shell burning had been computed, too. It could be demonstrated that explosions by the neutrino-driven mechanism can produce powerful supernovae with energies, radioactive nickel ejecta, and neutron-star masses and kick velocities in agreement with observations, in particular Supernova 1987A.

Core-collapse supernovae are among the most energetic events in the Universe and can be as bright as a galaxy. They mark the violent, explosive death of massive stars, whose iron cores collapse to the most exotic compact objects known as neutron stars and black holes. In this project self-consistent 3D simulations with state-of-the-art microphysics were performed for the explosion of a ~19 solar-mass star. It could be demonstrated that muon formation in the hot neutron star, which had been ignored in supernova models so far, leads to a faster onset of the explosion. The effects of muons thus over-compensate the delay of the explosion caused by low resolution, where numerical viscosity impedes the growth of hydrodynamic instabilities.

The FirstLight project at LRZ is a large database of numerical models of galaxy formation that mimic a galaxy survey of the high-redshift Universe, before and after the Reionization Epoch. This is the largest sample of zoom simulations of galaxy formation with a spatial resolution better than 10 pc. This database improves our understanding of cosmic dawn. It sheds light on the distribution of gas, stars, metals and dust in the first galaxies. This mock survey makes predictions about the galaxy population that will be first observed with future facilities, such as the James Webb Space Telescope and the next generation of large telescopes.

Two major events are responsible for what is considered the “golden age” of relativistic astrophysics. One is the detection of gravitational waves from merging neutron stars heralding the beginning of the multimessenger age. The other is the effort of the Event Horizon Telescope collaboration culminating in the first image of a black hole. Both events have been aided by simulations that require HPC. With this project, several studies could be conducted well alligned with these type of simulations expanding our knowledge about these important astrophysical events.

Neutron stars are ultracompact stars in which densities above the nuclear saturation densities are reached and that provide one of the best laboratories to test nuclear physics principles. Within this project, researchers perform 3+1-dimensional numerical-relativity simulations studying the last few orbits before the merger of two of these stars. In fact, a binary neutron star merger is one of the most energetic phenomena in our Universe and is accompanied by a variety of electromagnetic signatures and with characteristic gravitational-wave signatures. With the help of these simulations existing theoretical models can be developed and verified and the growing field of multi-messenger astronomy is supported. 

The intergalactic medium, the low density gas that lies between galaxies, contains vast information about how the universe evolved and when the first stars formed. In order to provide a solid theoretical platform for current and upcoming observations of the properties of this gas, a series of hydrodynamical cosmological simulations using the Nyx code were run on JUWELS on JSC. These simulations had an unprecedented dynamical range and used a novel approach to account for the challenging inhomogeneous radiation that must be included in these type of calculations.

Supernovae of Type Ia are modeled as thermonuclear explosions of a carbon-oxygen white dwarf stars. The way these trigger the explosive burning, however, is still unclear. This project performs hydrodynamic simulations that give insights into possible explosion mechanisms. With its pipeline extending from explosion simulation to the derivation of synthetic observables, the project allows for a direct comparison with astronomical observations thus scrutinizing the modeled scenarios.

The neighbourhood in the immediate vicinity of the Milky Way is known as the “Local Group”. It is a binary system composed of two averaged sized galaxies (the Milky Way and Andromeda) dominating a volume that is roughly ~7 Mpc in diameter. At a distance of around 15Mpc, the Virgo cluster comes into view as the main defining feature of our neighbourhood on these scales. Beyond Virgo, a number of well known and well observed clusters like Centaurus, Fornax, Hydra, Norma, Perseus and Coma dominate the night sky. This is our cosmic neighbourhood. The goal of this project is, for the first time, to perform targeted, state of the art hydro-dynamical simulations covering this special region of the universe and to compare the results with various…

Active galactic nuclei (AGN) are powerful emitters of photons in energy ranges from few millielectron volts (meV) to several teraelectron volts (TeV). These sources show variabilities as fast as a few minutes. It is believed that the emission originates from particles accelerated in shock waves in the jet of AGN. Observational data, however, is too sparse to constrain radiation models. Therefore, light curves (i.e. temporal data) are used to constrain models further. Using the Particle-in-Cell method to investigate shock collisions, this project aims at gaining more detailed insight into a special case of variability.

The outcome of a large set of cosmological, hydro-dynamical simulations from the project Magneticum now became made available to the general community through operating a cosmological simulation web portal. Users are able to access data products extracted from the simulations via a user-friendly web interface, browsing through visualizations of cosmological structures while guided by meta data queries helping to select galaxy clusters and galaxy groups of interest. Several services are available for the users: (I) ClusterInspect; (II) SimCut (raw data access); (III) Smac (2D maps); (IV) Phox (virtual X-ray observations, taking the specifications of various, existing and future X-ray telescopes into account.

Galaxy clusters are large reservoirs of galaxies. As such they are perfect objects of studies to unravel the mysteries of galaxy formation and evolution in dense environments. At ~50 million light-years away from Earth, the Virgo cluster, a gathering of more than a thousand galaxies, is our closest cluster-neighbour. Its proximity permits deep observations. Cosmological numerical simulations of the cluster constitute the numerical counterparts to be compared with observations to test our theoretical models. In such simulations, dark matter (nature of most of the matter in the Universe) and baryons (visible matter) follow physical laws to reproduce our closest cluster-neighbour and its galaxies in a simulated box across cosmic time.

Traditionally, numerical simulations of core-collapse supernovae have been performed with spherically symmetric initial models for the progenitor stars, because stellar evolution is computed with this restriction. Recently, however, it has been demonstrated that pre-collapse asymmetries in the convectively burning oxygen shell can have an impact on the explosion by enhancing turbulence behind the supernova shock. In this project researchers simulated the final seven minutes of oxygen burning and the subsequent collapse of a 19 solar-mass star in order to investigate the consequences of pre-collapse asymmetries for the supernova explosion.

Understanding turbulent gases and fluids is critical for a wide range of terrestrial and astrophysical applications. Here we present the world's largest turbulence simulation to date. This GCS Large-Scale Project on SuperMUC consumed 45 million core hours and produced 2 PB of data. It is the first and only simulation to bridge the scales from supersonic (Mach > 1) to subsonic (Mach < 1) flow and resolves the sonic scale (where the Mach number = 1). The sonic scale is a key ingredient for star formation models and may determine the size of filamentary structures in the interstellar medium.

The formation of the first galaxies marked the end of the cosmological dark ages. Radiation from the first stars ionized and heated inter-galactic gas. As these ionized gas bubbles grew and percolated, the whole Universe was transformed from a dark, cold, neutral state into a hot ionized one, about a billion years after the Big Bang. The SPHINX cosmological radiation-hydrodynamics simulations of the first billion years are designed to understand the formation of the first galaxies and how they contributed to reionization via the interplay of star formation, stellar radiation, and powerful supernova explosions that disrupt galaxies and allow their radiation to escape into inter-galactic space.

The "ray-by-ray" approximation is a widely used simplification of the time-dependent, six-dimensional transport of all neutrino species in core-collapse supernovae. It reduces the dimensionality of the computationally challenging problem by assuming that non-radial flux components are negligible. This leads to the solution of three-dimensional (radius-, energy-, and angle-dependent) transport equations for all angular directions of the spatial polar grid. Such a task can be extremely efficiently parallelized also on huge numbers of computing cores. In this project 3D simulations were performed to test this approximation and could demonstrate its validity.

Molecular clouds form out of the diffuse interstellar medium (ISM) within galactic disks and continuously accrete gas and interact with their surroundings as they evolve. Hence the evolution of turbulent, filamentary molecular clouds has to be modeled at the same time as the surrounding multiphase ISM. In the SILCC-ZOOM project, we simulate molecular cloud formation, the star formation within them, and their subsequent dispersal by stellar feedback on sub-parsec scales in 3D, AMR, MHD simulations with the FLASH code including self-gravity, radiative transfer, and a chemical network.

The age of multi-messenger gravitational wave astronomy has arrived. The simultaneous detection of gravitational and electromagnetic waves from merging neutron stars has illustrated the importance of having high resolution numerical relativity simulations, performed on SuperMUC, available to disentangle the complex interplay of nuclear physics, neutrino physics, and strong field gravity. Using these simulations, it is possible to study matter at densities unreachable with terrestrial experiments and determine the origin of the heavy elements in the universe.

The collision of two neutron stars is one of the most violent events in the Universe. The extreme conditions, with densities of about one hundred million tons per cubic centimeter and gravity hundred billion times that of Earth gravity, cannot be tested on Earth, which makes these events a perfect laboratory to study matter at extreme limits. Using advanced numerical relativity simulations, scientists study the phenomena close to the merger of the two neutron stars to extract information about the emitted gravitational wave and electromagnetic signals.

General relativity describes the gravitational interaction as the curvature of spacetime. This involves complicated partial differential equations, and consequently extreme scenarios can be treated only by numerical simulations. In this project spacetimes close to the critical threshold of black hole formation were evolved on SuperMuc. These computations were performed using bamps, a new massively parallel code for numerical relativity. The spacetimes constructed constitute the most extreme regime imaginable - that in which cosmic censorship itself may be violated and the black hole singularity could be seen by distant observers. 

Planetesimals are kilometre-sized planetary building blocks in the early solar system. Scientists pioneered a scenario in which turbulent concentrations of the icy and dusty material leads to sufficiently large densities in which self-gravity dominates over gas shear and tidal forces of the star. As a consequence, the material collapses spontaneously under its own weight into planetesimals. Therefore, the motion of many millions of particles in magneto-hydro-dynamically and particle driven turbulence and include the gravity among gas and particles are all simulated in one huge simulation. The goal is to link the observations of dust around young stars in a quantified way to an initial mass distribution of planetesimals.

An international group of scientists leverages high-performance computing to support current and future measurements of atomic photoionization cross-sections at various synchrotron radiation facilities, ion-atom collision experiments, together with plasma, fusion and astrophysical applications. In their work they solve the Schrödinger or Dirac equation using the R-matrix or R-matrix with pseudo-states approach from first principles. Cross-sections and rates for radiative charge transfer, radiative association, and photodissociation collision processes between atoms and ions of interest for several astrophysical applications are presented.

Modern simulations of galaxy formation, which simultaneously follow the co-evolution of dark matter, cosmic gas, stars, and supermassive black holes, enable us to directly calculate the observable signatures that arise from the complex process of cosmic structure formation. TNG50 is an unprecedented ‘next generation’ cosmological, magneto-hydrodynamical simulation -- the third and final volume of the IllustrisTNG project. It captures spatial scales as small as ~100 parsecs, resolving the interior structure of galaxies, and incorporates a comprehensive model for galaxy formation physics.

Hydrodynamical simulations of galaxy formation have now reached sufficient physical fidelity to allow detailed predictions for their formation and evolution over cosmic time. The aim of this project is to carry out a new generation of structure formation simulations, IllustrisTNG, that reach sufficient volume to make accurate predictions for clustering on cosmologically relevant scales, while at the same time being able to compute detailed galaxy morphologies, the enrichment of diffuse gas with metals, and the amplification of magnetic fields during structure growth.

The large amount of data returned by several space missions to the terrestrial planets has greatly improved our understanding of the similarities and differences between the innermost planets of our Solar System. Nevertheless, their interior remains poorly known since most of the data is related to surface processes. In the absence of direct data of the interior evolution of terrestrial planets, numerical simulations of mantle convection are an important mean to reconstruct the thermal and chemical history of the interior of the Earth, Moon, Mercury, Venus and Mars. In this project, run on Hornet of HLRS, researchers used the mantle convection code Gaia to model the thermal evolution of terrestrial planets and in particular the early stage…

Interstellar turbulence shapes the structure of the multi-phase interstellar medium (ISM) and is a key process in the formation of molecular clouds as well as the build-up of star clusters in their interior. The key ingredient for our theoretical understanding of ISM dynamics and stellar birth is the sonic scale in the turbulent cascade, which marks the transition from supersonic to subsonic turbulence and produces a break in the turbulence power spectrum. To measure this scale and study the sonic transition region in detail, scientists, for the first time, ran a simulation with the unprecedented resolution of 10,048³ grid cells.

Recently the first three-dimensional simulations have confirmed the long-standing hypothesis that the neutrino-driven mechanism, supported by violent hydrodynamic instabilities and turbulent mass flows, can explain supernova explosions of stars with more than 8−10 solar masses. Further consolidation of this mechanism and a deeper theoretical understanding of its functioning require the exploration of a broader variety of progenitor stars and of dependences on the initial conditions prior to iron-core collapse. In this Gauss project the influence of stellar rotation, perturbations in the convective oxygen-burning layer, and of large mass-infall rates due to high core compactness in very massive progenitor stars were explored.

The modelling of star formation and feedback processes such as supernova explosions is a longstanding problem in numerical simulations of cosmological structure formation because the internal structure of galaxies cannot be resolved in sufficient detail even on very powerful supercomputers. For this reason, star formation and stellar feedback are treated as so-called subgrid physics. The aim of our project is to combine standard recipes for star formation in simulations on cosmological scales with a subgrid-scale model for numerically unresolved turbulence, which allows us to study the influence of turbulence on star formation and the mixing of metals expelled by supernova explosions in galaxies. It is believed that, in addition to…

First self-consistent, first-principle simulations in three dimensions have provided support for the viability of the neutrino-driven mechanism as an explanation of supernova explosions of stars with more than 8−10 solar masses. While these results respresent fundamentally important progress in our understanding of how massive stars terminate their lives, the enormous complexity and computational demand of the involved neutrino physics set severe resolution limitations to current full-scale supernova models. In this project, the numerical convergence of the present simulations were investigated.

Leveraging the HPC infrastructure of LRZ, researchers at the Goethe University in Frankfurt/Main employ a series of in-house developed cutting-edge numerical methods to simulate in full general relativity the inspiral, merger, and collapse of neutron stars. The computationally intense, fully parallel simulations incorporate relativistic hydrodynamics, nuclear finite-temperature equations of state, and an approximate treatment of neutrino emission and absorption. The results, obtained by measuring gravitational waves, can provide important information on the properties of matter at nuclear densities.

An international team of scientists performed a series of Constrained Simulations to study Near Field Cosmology. These high-resolution simulations allowed the astrophysicists, for the first time, to study the formation of the Local Group in the right cosmic environment. 

The recent observations of gravitational waves (GWs) marked a breakthrough and inaugurated the field of GW astronomy. To extract information from a detection, the measured signal needs to be cross-correlated with a template family. However, due to the nonlinearity of Einstein’s equations, numerical simulations have to be used to study systems with gravitational fields strong enough to emit GWs. This project focused on the simulation of systems consisting of two neutron stars and investigated the effect of the mass ratio and the influence of the spin of the individual stars.

Researchers at the University of Münster investigated precession driven flows in planets by direct numerical simulations on the JUQUEEN cluster. Precession of the rotation axis is an often neglected driving mechanism for flows in planetary cores, a field of research were other scientists mainly focus on the influence of thermal or chemical effects. As an additional complication that moves the models closer to the physical reality, the project considered the spheroidal shape of the planet, whereas previous research has been focused on the idealized case of a perfect sphere.

What can we learn from some of the most powerful explosions in the universe? Researchers in Italy, USA, and Japan joined forces to study, via computer simulations in general relativity, what happens when two neutron stars in a binary system finally merge. Besides black holes, neutron stars are the most compact objects ever observed. Their collisions can produce bright electromagnetic emission and strong gravitational waves. Understanding how to relate the different signals with the properties of neutron stars may allow us to understand how matter behaves in conditions so extreme that cannot be reproduced on Earth.

Why do galaxies that live in the enormous structures known as galaxy clusters look different from normal, isolated galaxies, like our Milky Way? To answer this question, astrophysicists have created the Hydrangea simulations, a suite of 24 high-resolution cosmological hydrodynamical simulations of galaxy clusters. Containing over 20,000 cluster galaxies in unprecedented detail and accuracy, these simulations are giving astrophysicists a powerful tool to understand how galaxies have formed and evolved in one of the most extreme environments of our Universe.

Understanding the light emitted by (magnetically) active cool stars (‘M dwarfs’) is a major challenge for astrophysics. In this project, scientists use their PHOENIX/3D code to simulate the light emitted by a ‘box’ inside the outer layers of an active M dwarf in detail. The temperatures and pressures inside the box are taken from an existing gas dynamics simulation (including magnetic field effects) by S. Wedemeyer (Oslo). The computational requirements of detailed non-equilibrium 3D radiative transfer simulations are staggering and require the largest supercomputers on Earth.

Researchers finished the implementation and verification of a 3D non-local thermodynamic equilibrium (NLTE/3D) module for the PHOENIX/3D model atmosphere simulation code. The methods were extended to also allow NLTE modelling of molecular lines (here: CO) and then used to model the radiation from parameterized star-spots to investigate the effects of detailed 3D radiation transport on observables.

Space weather is an increasingly important aspect for our technology-dependent society. Modelling space weather is difficult, however, a Finnish team has succeeded in something that was said to be impossible: an accurate simulation of the large-scale near-Earth space environment. PRACE Tier-0 grant from Hazel Hen (HLRS, Stuttgart) both allowed the Vlasiator team to discover new space physics phenomena, and significantly helped in the acceptance of the second European Research Council grant awarded to the project PI in fall 2015.

Gravitational waves are ripples in spacetime, predicted by Einstein already a century ago. With the announcement earlier this year that gravitational waves had been successfully detected from two black holes merging, attention now turns to other potential sources of gravitational waves. Such sources include dramatic events that may have occurred very early in the history of the universe. Understanding these other sources also informs the design of future gravitational wave detectors, such as the European Space Agency (ESA) project eLISA.

The process of magnetic reconnection — when magnetic fields in plasma reconfigure and explosively release thermal and kinetic energy — is only just beginning to be understood. Professor Giovanni Lapenta has been carrying out simulations on SuperMUC of how these events can cause chain reactions that very quickly fill vast volumes of space. This data is now being verified with the recent NASA Magnetospheric MultiScale Mission that is measuring magnetic reconnection events around the Earth.

A simulation project, run on SuperMUC, targets the intrinsic physics of the chromosphere in order to understand its mass and energy budgets and transfer mechanisms. Elucidating these is a principal quest of solar physics, a necessary step towards better space-weather prediction, and of interest to general astrophysics using the Sun as a close-up Rosetta-Stone star and to plasma physics using the Sun and heliosphere as a nearby laboratory. The project aims at a breakthrough in our understanding of the solar chromosphere by developing sophisticated radiation-magnetohydrodynamic simulations.

An international research collaboration led by the University of Würzburg delved into the subjects of turbulence and particle acceleration in the solar wind by performing highly complex numerical simulations leveraging the particle-in-cell (PiC) approach, a technique used to solve a certain class of partial differential equations thus capable of studying these phenomena. In order to model the complex system of different waves, particles and electromagnetic fields self-consistently, the use of massive computing power such as provided by high performance computing system SuperMUC is inevitable.

The acceleration of charged particles is still one of the most important problems in astrophysics. Cosmic rays, which mainly consist of protons, show a broad spectrum with energies up to 10²¹ eV, which can be produced in collisionless shocks. However, many questions are still open regarding the acceleration process and the process of shock formation. To study this complex process with non-linear methods, researchers used JUQUEEN to investigate different aspects of the shock formation process and further applications.

Scientists of the Max Planck Institute for Astronomy in Heidelberg are using the HPC infrastructure of the Jülich Supercomputing Centre for extensive magneto-hydro-dynamical and million particle simulations of protoplanetary disks to study their evolution and properties. Findings are helping the researchers to understand the processes leading to the formation of planets, moons and asteroids. Their investigations will help to explain the observed diversity in planetary systems and in our own solar system.

Scientists of the German Aerospace Center Berlin (DLR) exploited the computing capacity of the petascale system Hornet of HLRS to study the convective dynamics and evolution of planetary interiors. The goal of the large-scale simulation project MATHECO (MAntle THErmo-chemical COnvection Simulations), which scaled to 54,000 compute cores of the supercomputer Hornet, was to gain further insights into the cooling history of planets and its influences on volcanic and tectonic surface processes.

Observations show that Earth is constantly bombarded by highly energetic particles that are called cosmic rays. A possible explanation for the origin of the cosmic rays as well as their energy distribution is particle acceleration at shock fronts. Several different physical processes take place there, but due to the large astrophysical distances it is, unfortunately, impossible to study these in-situ. One way out is large scale computer simulations.

A multi-million compute hours allocation by the Gauss Centre for Supercomputing on HPC system SuperMUC of the Leibniz Supercomputing Centre (LRZ) was used to carry out Aurora, a new set of radiation-hydrodynamical simulations of galaxy formation during reionization. Numerical simulations have emerged as the most powerful tools for the ab initio theoretical treatment of reionization. 

The Stellar Core-Collapse Group at the Max Planck Institute for Astrophysics (MPA) is able to conduct the presently most advanced 3D supernova simulations thanks to a suitably constructed description of the neutrino physics and a highly efficient, extremely well parallelized numerical implementation on petascale system SuperMUC. Because neither experiments nor direct observations can reveal the processes at the center of exploding stars, highly complex numerical simulations are indispensable to develop a deeper and quantitative understanding of this hypothetical “neutrino-driven explosion mechanism”, whose solid theoretical foundation is still missing.

A team of researchers has performed the largest simulations of unmagnetised shocks driven in astrophysical conditions to determine the parameters required to excite shocks in the laboratory, and studied the set of complex and nonlinear phenomena involved in these scenarios, such as magnetic field generation and particle acceleration. The simulations have been performed with the state-of-the-art particle-in-cell code OSIRIS.

A European team of scientists from Cologne, Garching, Heidelberg, Prague and Zurich used GCS HPC resources to model representative regions of disk galaxies using adaptive, three-dimensional simulations at unprecedented resolution and with the necessary physical complexity to follow the full life-cycle of molecular clouds. They aim to provide a self-consistent answer as to how stellar feedback regulates the star formation efficiency of a galaxy, how molecular clouds are formed and destroyed, and how galactic outflows are driven.

(Using GCS HPC resources, a group of scientist from a number of international institutes were able to prove that very weak magnetic fields can be efficiently amplified during different stages of cosmic evolution. 

(Type Ia supernovae, gigantic astrophysical explosions that completely disrupt one star and shine brighter than an entire galaxy consisting of 100 billion stars, have been successfully used to measure distances in the Universe. But what are the stars that give birth to Type Ia supernovae? The answer to this question remains elusive despite advances in modelling and observing these cosmic events over the past decades. From the perspective of theoretical modelling, only detailed multi-dimensional simulations of the explosion process on the most powerful supercomputers offer a way to tackle this long-standing problem. 

A team of about 20 scientists working in Europe, India, South Africa and the USA have been involved in an Astrophysics simulation project calculated on LRZ system SuperMUC. The obtained results will allow the efficient detection and identification of gravitational wave events, e.g. to tell apart black holes from neutron stars.

An international team of scientists at the Heidelberg Institute for Theoretical Studies (HITS), MIT, Harvard University and the University of Cambridge has carried out the “Illustris Simulation” on the SuperMUC and CURIE supercomputers, and created the largest and most sophisticated computational model of cosmic structure formation thus far.

In project Magneticum, scientists perform simulations of which the most computational intensive one covers a cosmic volume of 1 Gpc^3. This allows the researchers, for the very first time, to self consistently study galaxy clusters and groups, galaxies, and active galaxy nuclei (AGNs) within an enormously large volume of the Universe.

Scientists from the Albert Einstein Institute in Potsdam/Germany used HPC system SuperMUC to study the dynamics of compact-object binaries, i.e. neutron stars and black holes, and to improve our understanding of strong gravity. 

The HPC resources of HLRS Stuttgart enabled the world’s first global runs of the near-Earth space using a hybrid-Vlasov approach at highest resolutions. 

Scientists at the Max Planck Institute for Solar System Research in Göttingen employed a three-dimensional numerical model on GCS supercomputer Hermit of HLRS Stuttgart to investigate the heating process of the highly structured and dynamic corona. 

An international team of scientists used GCS supercomputing resources to study the evolution and fragmentation of clouds into stars. The degree of complexity, resulting from the mutual interaction of magnetic fields, gravity, and supersonic turbulence, is such that no complete theory of star formation is available to date. The best way to tackle this problem is to use powerful supercomputers such as petascale system SuperMUC of LRZ.

Accretion discs can power some of the most energetic phenomena in the universe and understanding how they work is very important for the comprehension of different astrophysical problems like how stars are formed or what happens in the central cores of galaxies.

Scientists used GCS supercomputing resources to perform a series of state-of-the-art constrained simulations of the first galaxies and their radiative effects in our Local Universe, among the largest and most detailed of their kind, following tens of billions of particles, while also modelling the complex physics involved in this process.

Scientists improved and combined methods to simulate the formation of the actual distribution of galaxies and galaxy clusters which allowed them to simulate the density distribution in the local universe up to distances of 670 million light-years.

To advance the so far limited knowledge of density probability distribution function and the power spectrum of compressible, supersonic turbulence, a team of astrophysicists compared hydrodynamic models with numerical resolutions of 256³–4096³ mesh points and with two distinct driving mechanisms, solenoidal (divergence-free) driving and compressive (curl-free) driving. By doing so, the scientists ran the world's largest simulation of supersonic turbulence on GCS supercomputers. 

Using hydrodynamic simulations on GCS supercomputers, a team of scientists from the Max-Planck-Institute for Radio Astronomy, Bonn, and Jülich Supercomputing Centre investigated the influences of surrounding gas onto the period of binary systems. 

Massive stars end their lives as core-collapse supernovae when the stellar core implodes to a neutron star and the stellar envelope is expelled. Using computer models, we have simulated the mixing processes occurring during the explosion without assuming any symmetry.

Numerical simulations are a crucial tool to understand the physics of gas turbulence and star formation: there is no analytic theory. More than six decades of spatial scales need to be described, which is best done with "adaptive resolution" codes on supercomputers. 

One of the cutting-edge problems in current astrophysical research is the formation and evolution of galaxies similar to our Milky Way Galaxy.