Microphysics in Computational Relativistic Astrophysics

Conference Date:
Monday, June 20, 2011 (All day) to Friday, June 24, 2011 (All day)
Scientific Areas:
Particle Physics

This workshop will bring together researchers in the field of numerical modeling and microscopic physics of matter and radiation at high densities where effects of general relativity play a central role.

The topics covered will include improved microscopic physics inputs (neutrino-matter interactions, equations of state, thermonuclear reaction rates) and computational methods (GRMHD, radiation transport, reaction networks) with an emphasis on approaches that allow for efficient implementation of the improvements in multi-D simulations of relativistic astrophysical systems.

Ernazar Abdikamalov, California Institute of Technology

Niayesh Afshordi, Perimeter Institute

Almudena Arcones, University of Basel

Pablo Cerda-Duran, Max Planck Institute for Astrophysics

Michael Deaton, Washington State University

Matthew Duez, Washington State University

Joshua Faber, Rochester Institute of Technology

Rodrigo Fernandez, Institute for Advanced Study

Francois Foucart, Cornell University

Filippo Galeazzi, Max Planck Institute for Gravitational Physics

Alexandros Gezerlis, University of Washington

Carsten Gundlach, University of Southampton

Ian Hawke, University of Southampton

Kai Hebeler, Ohio State University

Eric Hirschmann, Brigham  Young University

Charles Horowitz, Indiana University

Joseph Hughto, Indiana University

Lawrence Kidder, Cornell University

Kei Kotake, National Astronomical Observatory of Japan

Benjamin Lackey, University of Wisconsin-Milwaukee

Matthias Liebendrfer, University of Basel

Steve Liebling, Long Island University

Yeunhwan Lim, Stony Brook University

Pedro Marronetti, Florida Atlantic University

Gabriel Martnez-Pinedo, Helmholtzzentrum für Schwerionenforschung

Bronson Messer, Oak Ridge National Laboratory, Univiversity of Tennessee

Brian Metzger, Princeton University

David Neilsen, Brigham Young University

Jason Nordhaus, Princeton University

Evan O'Connor, California Institute of Technology

Richard O'Shaughnessy, University of Wisconsin-Milwaukee

Carlos Palenzuela, CITA

Jason Penner, University of Southampton

David Radice, Max Planck Institute for Gravitational Physics

Yasuhiro Sekino, KEK

Eric Schnetter, Perimeter Institute

Rishi Sharma, TRIUMF

Gang Shen, Los Alamos National Lab

Hong Shen, Nankai University

Kohsuke Sumiyoshi, Numazu National College of Technology

David Tsang, California Institute of Technology

Ernazar Abdikamalov, Caltech/LSU

A Monte Carlo Method for Radiation Transport

Almudena Arcones, University of Basel

Nucleosynthesis of Heavy Elements in Neutrino-Driven Winds and Neutron-Star Mergers

The energy generated by the r-process can impact the dynamics of neutron star mergers. Solving a full r-process network coupled with the hydrodynamics becomes the necessary but it is computational very expensive. We have developed a simple model that can be implemented into hydrodynamic simulations and gives a very good estimate of the r-process heating.

Pablo Cerda-Duran, Max-Planck-Institute for Astrophysics

Modeling QPOs in magnetar giant flares

Alfven oscillations of strongly magnetized neutron stars coupled to shear modes in the solid crust could possibly explain the quasi-periodic oscillations (QPOs) observed in the giant flares of soft gamma repeaters. We present results of two-dimensional simulations of Alfven torsional oscillations in magnetars, modeled as relativistic stars with a dipolar magnetic field. We use a general relativistic magnetohydrodynamics code in the anelastic approximation, which allows for an effective suppression of fluid modes and an accurate description of the Alfven waves. We discuss the coupling of the neutron star interior with the magnetosphere and the observational consequences.

Matthew Duez, Washington State University, Pullman

The challenges of realistic neutron star binaries

Black hole-neutron star (BHNS) binary mergers areimportant gravitational wave sources and (possibly) gamma ray burst progenitors.  Fully relativisticsimulations have only recently begun to try to capture neutron star physics beyond the polytrope approximation.  In this talk we discuss the numerical challenges of replacing polytropes with realistic neutron stars--particularly those relating to sharper neutron star surface features and to the effects of neutrino radiation--and we present the current status of simulations by the (Caltech-Cornell-CITA-WSU) SXS collaboration and how they are dealing with these issues.

Joshua Faber, Rochester Institute of Technology

Combining MHD and microphysics

I will discuss the techniques that can be used to include arbitrary equations of state in MHD simulations, particularly the ways in which one may perform conservative to primitive variable conversion numerically  for such simulations.

Rodrigo Fernandez, Institute for Advanced Study

Understanding the SASI with simple microphysics

A stalled core-collapse supernova shock is unstable to non-spherical perturbations, in what is known as the Standing Accretion Shock Instability (SASI). This instability is global and oscillatory, affecting the region between the protoneutron star surface and the shock.

I'll discuss several insights into this instability obtained by combining linear stability analysis and time-dependent simulations, using simple prescriptions for the microphysics that capture the essential physics of the problem.

Alexandros Gezerlis, University of Washington

Spin-polarized low-density neutron matter

Low-density neutron matter is relevant to the study of neutron-rich nuclei and neutron star crusts. Unpolarized neutron matter has been studied extensively over a number of decades, while experimental guidance has recently started to emerge from the field of ultracold atomic gases. We study population-imbalanced neutron matter (possibly relevant to magnetars and to density functionals of nuclei) applying a Quantum Monte Carlo method that has proven successful in the field of cold atoms. We report on the first ab initio simulations of superfluid low-density polarized neutron matter. For systems with small imbalances, we find a linear dependence of the energy on the polarization, the proportionality coefficient changing with the density. We also present results for the momentum and pair distributions of the two fermionic components.

Carsten Gundlach, School of Mathematics, University of Southampton

A formalism for weak solutions of GR elasticity

I review different approaches to the kinematics and dynamics of (hyper)elasticity in GR, and describe one that is now being implemented in joint work with Ian Hawke.

Ian Hawke, University of Southampton

Numrelasticity

Nonlinear numerical relativistic elasticity may be necessary for simulations including neutron star crusts. Basic simulations of large deformations in relativistic elastic matter will be detailed, and issues necessary for more realistic simulations covered. This work is in collaboration with Carsten Gundlach.

Kai Hebeler, The Ohio State University

Three-nucleon forces: From neutron matter to neutron stars

Charles Horowitz, Indiana University

Neutron Star Crust Microphysics

New equations of state (EOSs) from extensive virial and relativistic mean field calculations will be presented.  We construct thermodynamically consistent EOSs from slightly noisy free energy calculations, which satisfy the first law, and conserves entropy during adiabatic compression.  However this requires a very careful procedure of numerically smoothing the entropy and then integrating the entropy to generate consistent free energies.  We discuss various features of the EOS in different density, temperature, and proton fraction regimes.   We compare the adiabatic index for our EOSs with those of the Lattimer Swesty and H. Shen et al. EOSs.  We do not find a first order liquid vapor phase transition for the astrophysical EOS.  Finally, we discuss neutrino interactions that are consistent with our EOSs.  At low density, we present model independent neutrino responses that are based on the viral expansion.

Joseph Hughto, Indiana University

Using GPUs to accelerate molecular dynamics simulations

GPUs can offer a less costly solution to large-scale calculations of astrophysical systems.  I will outline the basics of the CUDA libraries and also compare with various metrics our in-development GPU code for molecular dynamics versus our hybrid OpenMP/MPI version.

Kei Kotake, National Astronomical Observatory of Japan

Recipes to energize core-collapse supernova explosions

Recent multidimensional supernova simulations seem to support an assumption that the neutrino-driven mechanism might work to blow up massive stars. However the explosion energies obtained in those simulations are usually not enough to account for the canonical explosion energy of 10^51 ergs. In this contribution we'd like to address whether some new physical elements so far ignored in the supernova simulations would or would not have an impact on the neutrino-heating mechanism such as the effects of neutrino self-interactions nuclear burning and the turbulent heatingdue to the magneto-rotational instability. These effects are included in our 2D simulations with the spectral neutrino transport (Suwa et al. (2010)).In addition we will report our 3D results based on the 3D version of the code and discuss their potential impacts on the explosion mechanism. Based on these results we will compute the gravitational radiation and neutrinoemission and then discuss some prospects towards multi-messenger astronomyof supernova explosions.

James Lattimer, Stony Brook University

Neutron Star Mass and Radius Constraints for the Dense Matter Equation of State

Recent discoveries, including a 2 solar mass pulsar, rapid cooling in the Cas A supernova remnant, and estimates of masses and radii from photospheric radius expansion bursts and thermal emissions from neutron stars, are able to constrain significantly the properties of dense matter.  Implications for the pressure-density relation and properties of superfluids in neutron star interiors will be discussed.

Matthias Liebendrfer, University of Basel

3D Supernova Models

Gabriel Martnez-Pinedo, GSI Helmholtzzentrum fr Schwerionenforschung

Nucleosynthesis and Short Gamma-Ray Burst Central Engines

Massive accretion disks may form from the merger of neutron star (NS)-NS or black hole-NS binaries, or following the accretion-induced collapse (AIC) of a white dwarf.  These disks, termed hyper-accreting' due to their accretion rates up to several solar masses per second, may power the relativistic jets responsible for short duration gamma-ray bursts.  Using 1D time-dependent calculations of hyper-accreting disks, I show that a generic consequence of the disk's late-time evolution is the development of a powerful outflow, powered by viscous heating and the recombination of free nuclei into Helium.  These outflows - in additional to any material dynamically-ejected during the merger - synthesize heavy radioactive elements as they expand into space.  Nuclear heating from the r-process  is not yet incorporated in merger simulations, yet has important consequences both for the dynamics of late fall-back' accretion and in powering a supernova-like transient (kilonova')  1 day following the merger or AIC.

Bronson Messer, University of Tennessee, Oak Ridge National Laboratory

Weak interaction Physics in Large-Scale Core-Collapse

Brian Metzger, Princeton University

Nucleosynthesis and Short Gamma-Ray Burst Central Engines

Massive accretion disks may form from the merger of neutron star (NS)-NS or black hole-NS binaries, or following the accretion-induced collapse (AIC) of a white dwarf.  These disks, termed hyper-accreting' due to their accretion rates up to several solar masses per second, may power the relativistic jets responsible for short duration gamma-ray bursts.  Using 1D time-dependent calculations of hyper-accreting disks, I show that a generic consequence of the disk's late-time evolution is the development of a powerful outflow, powered by viscous heating and the recombination of free nuclei into Helium.  These outflows - in additional to any material dynamically-ejected during the merger - synthesize heavy radioactive elements as they expand into space.  Nuclear heating from the r-process  is not yet incorporated in merger simulations, yet has important consequences both for the dynamics of late fall-back' accretion and in powering a supernova-like transient (kilonova')  1 day following the merger or AIC.

David Neilsen, Brigham Young University

More on binaries from one camp work

Jason Nordhaus, Princeton University

Recent advances in core-collapse supernova theory

For approximately half a century, core-collapse supernovae have posed a vexing puzzle for theorists despite being a major ingredient (and uncertainty) in fields ranging from stellar and galaxy evolution to the interstellar medium.  Historically, advances in core-collapse theory have been linked to advances in computing power and software.  Supernovae are inherently multi-dimensional objects in which neutrino transport, gravity, hydrodynamic instabilities and convection play important roles. Three-dimensional simulations incorporating sufficient physical fidelity require extensive high-performance computing resources and codes efficient enough to use the associated architecture.  In this talk, I will highlight recent advances in the field.  In particular, I will discuss the dependence of spatial dimension on the viability of the neutrino mechanism and the origin  of pulsar kicks.

Evan O'Connor, Caltech

Neutrino oscillations and the CCSN mechanism

Richard O'Shaughnessy, University of Wisconsin-Milwaukee

Microphysics to macrophysics: Astrophysics and gravitational wave science opportunities in the advanced detector era and beyond

Carlos Palenzuela, CITA

Electromagnetic interaction of binary neutron star magnetospheres

Neutron star mergers represent one of the most promising sources of gravitational waves (GW), while that the presence of strong magnetic fields may offer the possibility of a characteristic electromagnetic signature allowing for concurrent detection. In this talk will be presented a new hybrid-passive approach to match the full GR-MHD evolutions of the binary neutron star mergers to the force-free equations in order to study numerically the dynamics and interaction of their magnetospheres.

Jason Penner,University of Southampton

Relativistic Magnetohydrodynamic  Bondi--Hoyle Accretion

I present a relativistic study of axisymmetric magnetohydrodynamic Bondi--Hoyle accretion onto a moving Kerr black hole. The equations of general relativistic magnetohydrodynamics are solved using high resolution shock capturing methods, involving the use of linearised Riemann solvers. In this study I use the ideal MHD limit, which assumes no viscosity and infinite conductivity. The fluid flow is completely specified by the adiabatic constant $Gamma$, the asymptotic speed of sound $c_s^infty$, and the plasma beta parameter $beta_P$. In particular I restrict the investigation to asymptotically supersonic flows where $v_infty ge c_rms^infty$. To determine the stability of the flow I measure the accretion rates of the energy, and mass. The models presented in this study exhibit a matter density depletion in the downstream region of the black hole which tends to vacuum in convergence tests. This is a feature due to the presence of the magnetic field, more specifically the magnetic pressure, which is not seen in purely hydrodynamic studies. The models investigated present a tendency towards a steady state, which is in agreement with previous studies performed by Font and Iban'ez (1998) using a purely hydrodynamic model.

David Radice, Max Planck Institute for Gravitational Physics

Discontinuous Galerkin methods for general relativistic hydrodynamics

I will present the formalism needed for the application of discontinuous Galerkin methods to general relativistic hydrodynamics and the results obtained in the spherically symmetric case.

Exploring equations of state in neutron star inspiral

For gravitational waveforms from binary neutron star inspiral, the cold equation of state (EOS) captures the relevant microphysics. Variation in the EOS can modify the inspiral waveform, starting before numerical simulations are practical and continuing through to the coalescence. I will discuss the impact of varying the EOS on gravitational waves, using both analytic (post-Newtonian) and numerical results. I will also compare the piecewise-polytropic equations of state used so far with recent EOS constraints and discuss future choices.

Erik Schnetter, Perimeter Institute

The Einstein Toolkit

The Einstein Toolkit Consortium is developing and supporting open software for relativistic astrophysics. Our aim is to provide the core computational tools that can enable new science, broaden the community, facilitate interdisciplinary research, and take advantage of emerging petascale computers and advanced cyberinfrastructure.

The Einstein Toolkit currently consists of an open set of over 100 components for computational relativity along with associated tools for simulation management and visualization. The toolkit includes a vacuum spacetime solver, a relativistic hydrodynamics solver, along with components for initial data, analysis, and computational infrastructure. These components have been developed and improved over many years by many different contributors.

Rishi Sharma, TRIUMF

An effective theory for the neutron star inner crust

The inner crust of neutron stars has a remarkable property that it is crystalline as well as superfluid. I will describe the low energy theory of systems with this property in general, and describe how to relate the low energy constants of the theory to derivatives of the free energy with respect to lattice shape and chemical potentials. As an application, I will discuss the mixing of lattice and superfluid modes in the neutron star inner crust.

Gang Shen, Los Alamos National Lab

Equation of State and Neutrino Opacity in Core Collapse Supernova

We present new equations of state (EOS) of nuclear matter for a wide range of temperatures densities and proton fractions for use in supernova and neutron star merger simulations. We employ a full relativistic mean field (RMF) calculation for matter at intermediate density and high density and the Virial expansion of a nonideal gas for matter at low density. We tabulate the resulting EOS in the temperature range T = 0 - 80 MeV the density range nB = 10âˆ’13- 1.6 fmâˆ’3 and the proton fraction range YP = 0 - 0.56. We have generated two distinct EOS tablesbased on NL3 and FSUGold effective interactions respectively and are considering a new EOS based on IUFSU effective interaction or its variation. These EOS tables cover large parameter spaces in the EOS systematically in the effective interactions approach. We compare in detail these EOS along with existing EOS for the thermodynamic properties composition matching to existing low density nuclear statistical equilibrium EOS down to 100 g/cm3 and nulcear reaction network at low temperature. We also present the adiabatic compression tests for our EOS.We discuss neutrino response consistent with underlying EOS. For Virial EOS at low densitiesthe neutrino interactions with nucleon and nuclei may be included readily at longwavelength limit.For matter at higher densities nuclear medium corrections to the neutrino interactions are includedin random phase approximations (RPA). For vector current channel the RPA corrections come fromone-particle-hole excitation whileas for axial vector current multi-partile-hole excitations dominateand extend the response to higher frequency in timelike region. The latter could be included viaintroduction of a relaxation time for the quasiparticle. We will show the effects on the neutrino mean free path and energy loss.

Hong Shen, Nankai University

Relativistic EOS for Supernovae Simulations

We construct the relativistic equation of state (EOS) of dense matter covering a wide range of temperature proton fraction and density for the use of core-collapse supernova simulations. The study is based on the relativistic mean-field (RMF) theory which can provide an excellent description of nuclear matter andfinite nuclei. The Thomas-Fermi approximation is adopted to describe the non-uniform matter which is composed of a lattice of heavy nuclei.We present two types of results. The first one takes into account only the nucleon degree of freedom while the second one considers additional contributions from Lambda hyperons. We tabulate the resulting EOS with an improved design of ranges and grids.

Kohsuke Sumiyoshi, Numazu National College of Technology

Progress of EOS tables for neutrino-radiation hydrodynamics of core-collapse supernovae

I would like to overview the progress of the EOS tables for core-collapse supernovae and their influence clarified by these EOS developments.  Some topics I try to cover include the neutrino signal from the black hole formation as well as the composition in supernova cores.  We would to like hear needs and comments from users of the series of Shen EOS tables for further developments.  I would like to report also on recent development of our numerical code of the neutrino-transfer calculation in 3D.

David Tsang, California Institute of Technology

Excitation of Neutron Star Modes During Binary Inspirals

Funding provided in part by: