ASTROPHYSICS

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.

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.

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 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. 

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.

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.

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.

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 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.

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. 

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.

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.

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. 

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.