Solving the Boltzmann Equation for Neutrino Transport in Relativistic Astrophysics

Institute for Computational and Experimental Research in Mathematics (ICERM)

https://icerm.brown.edu/topical_workshops/tw-24-sbe/
July 8, 2024 - July 12, 2024
Monday, July 8, 2024
  • 8:50 - 9:00 am EDT
    Welcome
    11th Floor Lecture Hall
    • Session Chair
    • Brendan Hassett, ICERM/Brown University
  • 9:00 - 9:45 am EDT
    Radiation Transfer Methods for Relativistic Spacetimes
    11th Floor Lecture Hall
    • Shane Davis, University of Virginia
    Abstract
    I will review efforts to model radiation transfer in relativistic spacetimes, describing different methods and approaches. I will discuss the pros and cons of these methods in their application to accreting black hole systems and report on recent results solving the transfer equation directly. I will endeavor to highlight some points of contact between photon radiation transfer applications in accreting systems and neutrino transport in core collapse and compact object mergers.
  • 10:00 - 10:30 am EDT
    Coffee Break
    11th Floor Collaborative Space
  • 10:30 - 11:15 am EDT
    Monte Carlo transport for post-merger and collapsar disks
    11th Floor Lecture Hall
    • Jonah Miller, Los Alamos National Laboratory
    Abstract
    The 2017 detection of the in-spiral and merger of two neutron stars was a landmark discovery in astrophysics. Through a wealth of multi-messenger data, we now know that the merger of these ultracompact stellar remnants is a central engine of short gamma ray bursts and a site of r-process nucleosynthesis, where the heaviest elements in our universe are formed. The radioactive decay of unstable heavy elements produced in such mergers powers an optical and infra-red transient: The kilonova. One key driver of nucleosynthesis and resultant electromagnetic afterglow is wind driven by an accretion disk formed around the compact remnant. Neutrino transport plays a key role in setting the electron fraction in this outflow, thus controlling nucleosynthesis. Collapsars are black hole accretion disks formed after the core of a massive, rapidly rotating star collapses to a black hole. These dramatic systems rely on much the same physics and modeling as post-merger disks, and can also be a key driver of r-processes nucleosynthesis. I present recent progress in modeling these enigmatic systems, with an emphasis on both the impact and techniques of detailed Monte Carlo neutrino transport.
  • 11:30 am - 12:15 pm EDT
    TBA
    11th Floor Lecture Hall
    • Irene Gamba, University of Texas at Austin
  • 12:30 - 2:30 pm EDT
    Lunch/Free Time
  • 2:30 - 3:00 pm EDT
    TBA
    11th Floor Lecture Hall
    • Sanjana Curtis, UC Berkeley
  • 3:10 - 3:25 pm EDT
    A Monte-Carlo based relativistic neutrino radiation hydrodynamics simulation for black-hole disk systems
    Short Talk - 11th Floor Lecture Hall
    • Kyohei Kawaguchi, Max Planck Institute for Gravitational Physics (AEI, Potsdam-Golm)
    Abstract
    Accurately solving neutrino radiation is a key ingredient for the quantitative understanding of the post-merger physics of neutron star binaries. For this purpose, we develop a new relativistic neutrino radiation hydrodynamics code based on the Monte-Carlo algorithm employing our scheme to achieve the second-order accuracy in time. In particular, in this code, neutrino/anti-neutrino pair process including electron-type neutrinos is dynamically taken into account. In the talk, we'll demonstrate that our code reproduces thermal equilibrium states in a wide range of setups in the physically correct manner. We'll then show our preliminary results applying our code to black-hole disk systems formed in neutron star binary mergers.
  • 3:30 - 4:00 pm EDT
    Coffee Break
    11th Floor Collaborative Space
  • 4:00 - 4:15 pm EDT
    AsterX: a new open-source GPU-accelerated GRMHD code for dynamical spacetimes
    Short Talk - 11th Floor Lecture Hall
    • Jay Kalinani, Center for Computational Relativity and Gravitation, Rochester Institute of Technology
    Abstract
    With an increasing demand of extensive parallel computing in numerical simulations addressing various astrophysical problems, codes which can efficiently work on GPUs are the need of the hour. In this talk, I will discuss the salient features of a new open-source general relativistic magnetohydrodynamic (GRMHD) code AsterX, which is built upon CarpetX, a new driver for the Einstein Toolkit. AsterX is based on the flux-conservative Valencia formulation, considering staggered vector potential evolution. It designed to work on GPUs and also takes advantage of the block-structured adaptive mesh refinement provided by CarpetX through the AMReX framework. I will also discuss the various stringent 1D, 2D and 3D GRMHD tests performed with AsterX on the Frontier cluster, and also present scaling results.
  • 4:20 - 4:50 pm EDT
    TBA
    11th Floor Lecture Hall
  • 5:00 - 6:30 pm EDT
    Reception
    11th Floor Collaborative Space
Tuesday, July 9, 2024
  • 9:00 - 9:45 am EDT
    Neutrino Quantum Kinetics
    11th Floor Lecture Hall
    • Irene Tamborra, University of Copenhagen
    Abstract
    Neutrinos change their flavor, while propagating in the core of compact astrophysical sources, such as core-collapse supernovae and neutron star mergers. Recent developments on the modeling of neutrino quantum kinetics in compact astrophysical sources, as well as its impact on the stellar dynamics and synthesis of the heavy elements will be reviewed.
  • 10:00 - 10:30 am EDT
    Coffee Break
    11th Floor Collaborative Space
  • 10:30 - 11:15 am EDT
    TBA
    11th Floor Lecture Hall
    • Sherwood Richers, University of Tennessee, Knoxville
  • 11:25 - 11:30 am EDT
    Group Photo (Immediately After Talk)
    11th Floor Lecture Hall
  • 11:30 am - 2:00 pm EDT
    Lunch/Free Time
  • 2:00 - 2:30 pm EDT
    Efficient numerical methods for the Boltzmann equation
    11th Floor Lecture Hall
    • Giacomo Dimarco, University of Ferrara
    Abstract
    We present a numerical method for solving the unsteady Boltzmann equation describing rarefied gas dynamics flows based on the combination of a wieghted particle approach on a Cartesian lattice and a fast spectral schemes for the collisional integral. We will also discuss the extension of such method to the case of electromagnetic conducting fluids and how to take into account the quantification of uncertainty in these models. Several numerical tests will explore the capability of the scheme proposed in modeling transport phenomena.
  • 2:40 - 2:55 pm EDT
    TBA
    Short Talk - 11th Floor Lecture Hall
  • 3:00 - 3:20 pm EDT
    Coffee Break
    11th Floor Collaborative Space
  • 3:20 - 3:50 pm EDT
    Jet launching from binary neutron star mergers: Incorporating neutrino transport and magnetic fields
    11th Floor Lecture Hall
    • Virtual Speaker
    • Milton Ruiz, University of Valencia
    Abstract
    We perform general relativistic, magnetohydrodynamic (GRMHD) simulations of merging binary neutron stars incorporating neutrino transport and magnetic fields. Our new radiative transport module for neutrinos adopts a general relativistic, truncated-moment (M1) formalism. The binaries consist of two identical, irrotational stars modeled by the SLy nuclear equation of state (EOS). They are initially in quasicircular orbit and threaded with a poloidal magnetic field that extends from the stellar interior into the exterior. We insert neutrino processes shortly after the merger and focus on the role of neutrinos in launching a jet following the collapse of the hypermassive neutron star (HMNS) remnant to a spinning black hole (BH). We treat two microphysical versions: one (a ``warm-up"") evolving a single neutrino species and considering only charged-current processes, and the other evolving three species $(\nu_e, \bar{\nu}_e, \nu_{\rm x})$ and related processes. We trace the evolution until the system reaches a quasiequilibrium state after BH formation. We find that the BH + disk remnant eventually launches an incipient jet. The electromagnetic Poynting luminosity is $\sim 10^{53} \rm \, erg\, s^{-1}$, consistent with that of typical short gamma-ray bursts (sGRBs). The effect of neutrino cooling shortens the lifetime of the HMNS, and lowers the amplitude of the major peak of the gravitational wave (GW) power spectrum somewhat. After BH formation, neutrinos help clear out the matter near the BH poles, resulting in lower baryon-loaded surrounding debris. The neutrino luminosity resides in the range $\sim 10^{52-53} \rm \,erg\,s^{-1}$ once quasiequilibrium is achieved. Comparing with the neutrino-free models, we observe that the inclusion of neutrinos yields similar ejecta masses and is inefficient in carrying off additional angular momentum.
  • 4:00 - 5:00 pm EDT
    Open Discussion
    Open Discussion - 11th Floor Lecture Hall
Wednesday, July 10, 2024
  • 9:00 - 9:30 am EDT
    Understanding neutron-star mergers by long-term numerical relativity simulations
    11th Floor Lecture Hall
    • Masaru Shibata, Albert Einstein Institute
    Abstract
    I will summarize our current understanding of the merger and post-processes for neutron-star binaries by introducing our latest results of numerical simulations. I will pay particular attention to nucleosynthesis of heavy elements and kilonovae, and give predictions for the future observations.
  • 9:40 - 9:55 am EDT
    Multi-group neutrino transport in hypermassive neutron star simulations
    Short Talk - 11th Floor Lecture Hall
    • Patrick Chi-Kit Cheong, UC Berkeley
    Abstract
    Energy-integrated two-moment neutrino transport schemes are getting popular in neutron star merger simulations. However, it is still unclear how accurate they are compared to energy-dependent neutrino transport. In this talk, I will briefly present the key elements of both energy-integrated and energy-dependent neutrino transport schemes in the GRRMHD code Gmunu. In addition, I will compare the post-merger simulations with these schemes.
  • 10:00 - 10:30 am EDT
    Coffee Break
    11th Floor Collaborative Space
  • 10:30 - 11:00 am EDT
    Simulating collapsars with neutrino transport
    11th Floor Lecture Hall
    • Danat Issa, Northwestern University
    Abstract
    The origin of heavy elements synthesized via rapid neutron capture process (r-process) is one of the longstanding questions in astronomy. So far, the only confirmed astrophysical sites of r-process nucleosynthesis are neutron star mergers, thanks to the multimessenger detection in 2017. However, there is a another promising site - dying massive stars, or collapsars, which were first invoked as a model to explain long gamma ray bursts. Here, we are going to present our work in modeling the collapsar explosions using 3-dimensional general relativistic magnetohydrodynamics simulations.
  • 11:10 - 11:25 am EDT
    Progenitor dependence of neutrino heating in core-collapse supernovae in 1D, 2D, and 3D: the role of compactness
    Short Talk - 11th Floor Lecture Hall
    • Luca Boccioli, University of California, Berkeley
    Abstract
    In this talk I will present the progenitor dependence of neutrino heating in the gain region of CCSNe. I will show that progenitors with higher compactness generate more neutrino heating, and therefore result in successful explosions. I will then analyze the interplay between neutrino heating and neutrino-driven convection using a simple semi-analytical model. Finally, I will show how some 1D models can be used to produce a similar time-dependent neutrino heating in order to achieve an explosion, and compare them to other widely used 1D models that instead use different prescriptions to trigger the explosion.
  • 11:30 am - 2:00 pm EDT
    Lunch/Free Time
  • 2:00 - 2:30 pm EDT
    Neutrinos in magnetically driven core-collapse supernovae
    11th Floor Lecture Hall
    • Virtual Speaker
    • Martin Obergaulinger, University of Valencia
    Abstract
    Neutrinos and magnetic fields may play similarly important roles in the collapse and explosion of a subset of massive stars. Determining the explosion mechanism as well as its impact on the nucleosynthesis and the propagation of the ejecta requires long-time simulations. I will present such models performed for several sets of pre-collapse models and describe the neutrino physics that went into them, including new developments on the minimally implicit time integration of the stiff neutrino-matter interaction terms.
  • 2:40 - 2:55 pm EDT
    Expanding the Boltzmann equation to include neutrino flavor evolution
    Short Talk - 11th Floor Lecture Hall
    • Marie Cornelius, University of Copenhagen
    Abstract
    Neutrinos, despite their weakly interacting nature, play a crucial role in core-collapse supernovae and neutron star mergers. In these dense environments, the neutrino number density is so large that the neutrino coherent forward scattering triggers flavor conversions. In this talk, I will explain how we can expand on the Boltzmann treatment to include neutrino self-interactions, using a quantum-kinetic approach. I will discuss recent developments related to the implications that neutrino quantum kinetics has on the symmetries of the system and the neutrino properties.
  • 3:00 - 3:20 pm EDT
    Coffee Break
    11th Floor Collaborative Space
  • 3:20 - 3:35 pm EDT
    TBA
    Short Talk - 11th Floor Lecture Hall
    • Somdutta Ghosh, NC State University
  • 3:40 - 3:55 pm EDT
    Self-consistent muon contributions in astrophysical simulations with radiation transport and accurate neutrino microphysics
    Short Talk - 11th Floor Lecture Hall
    • Harry Ho-YIN Ng, Institute for Theoretical Physics, Goethe-Universität Frankfurt
    Abstract
    Muons are expected to play a role in binary mergers of neutron stars and in core-collapse supernovae, but have so far been neglected in realistic simulations of binary mergers. We present the methodology and implementation of a self-consistent general-relativistic approach to compute the muon contributions in astrophysical simulations with radiation transport and accurate neutrino microphysics. In particular, we report the development and testing of a five-species moment-based radiation transport (M1) method, alongside the consistent inclusion of muons into the equation of state and corresponding weak interactions.
  • 4:00 - 4:15 pm EDT
    A general-relativistic full Boltzmann solver based on the finite volume method
    Short Talk - 11th Floor Lecture Hall
    • Arthur Offermans, KU Leuven
    Abstract
    Simulations of astrophysical systems where neutrinos play a significant role, like core-collapse supernovae, would ideally solve the neutrino transport equation fully, i.e. solve the full Boltzmann equation. Because of its very high computational cost (6+1D), simulations generally rely on approximations of the equation that are more affordable. It is however difficult to estimate what is lost through these approximations if we do not have access to a full solution. Solving the full equation would also enable a more accurate study of the impact of neutrinos on the phenomenon that is considered. Therefore, we developed a multidimensional full Boltzmann solver based on the Finite Volume method within the GRMHD simulation code Gmunu in order to perform those more accurate simulations. We present our solver, its performance on some first test cases and compare these results to the M1 radiation transport scheme.
  • 4:20 - 5:00 pm EDT
    Open Discussion
    Open Discussion - 11th Floor Lecture Hall
Thursday, July 11, 2024
  • 9:00 - 9:30 am EDT
    Classical Neutrino Kinetics in Core Collapse Supernovae, The Ultimate Goal: Rationale, Requirements, Constraints, Implementations, and Outlook
    11th Floor Lecture Hall
    • Anthony Mezzacappa, University of Tennessee, Knoxville
    Abstract
    It is now well established that neutrinos can drive core collapse supernova explosions and likely do for the lion’s share of observed events in the Universe. They are center stage in the modeling of core collapse supernovae and dominate the computational cost in all realistic models, given the need for a kinetics treatment of neutrino production, transport, and interaction in the cores of massive stars. Neutrino mean free paths range over orders of magnitude, and a fluid description is not accurate except in the innermost regions of these cores. The ultimate classical description of such kinetics would be achieved by solving the Boltzmann kinetic equations for all flavors of neutrinos and antineutrinos produced. Boltzmann kinetics would then provide a sound foundation for the extension to quantum kinetics in order to incorporate neutrino flavor transformations that are expected to occur, which may impact one or all of the following: the explosion mechanism, nucleosynthesis, and terrestrial neutrino signatures. The modeling of neutrino kinetics in core collapse supernovae is compounded by the fact that lepton number and energy must be conserved simultaneously and that the neutrino distribution functions must be bounded given the Fermi-Dirac statistics obeyed by these Fermions. Success in arriving at implementations of Boltzmann neutrino kinetics in future core collapse supernova models will require reformulations of the fundamental equations and the development of discretizations for these equations, that conserve lepton number and energy, are realizable – i.e., maintain boundedness of the neutrino distributions – and are computationally efficient. I will discuss each of these topics, as well as indicate progress to date in achieving our ultimate goal, by our group and others.
  • 9:40 - 9:55 am EDT
    Grey relativistic M1 neutrino transport in the BAM code: application to low mass binary neutron star merger
    Short Talk - 11th Floor Lecture Hall
    • Federico Schianchi, University of Potsdam
    Abstract
    Neutrino interactions are essential for an accurate understanding of binary neutron star merger ejecta and post-merger dynamics. We recently extended the infrastructure of the well-established numerical-relativity code BAM, that until recently neglected neutrino-driven interactions. We included a first-order multipolar radiation transport scheme (M1). After testing our implementation on a set of standard scenarios, we applied it to the evolution of low-mass binary systems, and we performed an analysis of ejecta properties. We found an important high electron fraction component of the ejecta, with a persistent wind taking place from the upper face of the disk for the whole duration of the simulation.
  • 10:00 - 10:30 am EDT
    Coffee Break
    11th Floor Collaborative Space
  • 10:30 - 11:00 am EDT
    Fast Evaluation of the Boltzmann Collision Operator Using Data Driven Reduced Order Models
    11th Floor Lecture Hall
    • Alexander Alekseenko, California State University Northridge
    Abstract
    The kinetic Boltzmann equation models macroscopic behavior of gas by averaging individual molecular interactions. It describes the state of gas using seven-dimensional velocity distribution function in three space, three velocity and one temporal variables and is believed to be the most accurate model of non-continuum gas. The flip side of its descriptive power is that a seven-dimensional velocity distribution function is difficult to discretize. As a result, practical solutions of kinetic equations continue to be challenging in three dimensions in complex domains and in applications to complex flows. An additional major difficulty continues to be the evaluation of the multifold integral operator describing the effect of molecular collisions. Low rank tensor approximations emerged recently as a promising approach to reduce effective dimensionality of discrete solutions and accelerate numerical computation of high dimensional problems. Low rank approximations were applied to discretization of the velocity distribution function with some success. At the same time, attempts to compress the collision operator using higher order singular value decomposition usually fail to provide significant savings do the properties of the operator. A possible alternative is the development of reduced order models (ROMs) based on low rank representation of solutions that is specific for the problem at hand. A single evaluation of a ROM for the collision operator requires O(K^3) operation where K is the size of the ROM basis. This becomes prohibitively expensive for K>100 compared to the O(M^2) full rank approaches where M is the total number of discrete velocity points. However, in practice, K<50, and the ROM can provide up to two orders of magnitude of speedup compared to fully discrete methods. Other ideas for compression of kinetic equations include the use of artificial neural networks. In this talk we will introduce ROMs for the kinetic Boltzmann equation as well as other ideas and will highlight our recent work in development of ROMs for solving the Boltzmann equation in zero and one spatial variables.
  • 11:10 - 11:25 am EDT
    Towards a General Relativistic Boltzmann Transport for Binary Neutron Star Mergers
    Short Talk - 11th Floor Lecture Hall
    • Maitraya Bhattacharyya, The Pennsylvania State University
    Abstract
    We present a new neutrino transport code for binary neutron star merger simulations for the numerical relativity code AthenaK. We use finite element and spectral approaches to handle the angular dependence while energy discretization is handled using a finite volume scheme. We employ an asymptotic-preserving discontinuous Galerkin (DG) method for the spatial discretization to ensure correct behavior in the diffusion-dominated regime. A semi-implicit time stepping scheme is used to handle the stiff and non-stiff sources correctly. In the first part of the talk we describe the two approaches for angular discretization: the finite-element method in angle (FEMN) and filtered spherical harmonics (FPN) with an emphasis on positivity preservation for multi-energy schemes. We also describe a strategy to obtain the two moments method (M1) from the formulated equations. We then compare the efficacy of the three approaches using various toy problems in the presence of a moving medium and general relativity.
  • 11:30 am - 2:00 pm EDT
    Lunch/Free Time
  • 2:00 - 2:30 pm EDT
    Core-collapse supernovae as probes of (not only) non-standard neutrino physics
    11th Floor Lecture Hall
    • Anna Suliga, University of California, Berkeley
    Abstract
    Core-collapse supernovae are one of the most complex phenomena in the Universe. Not only are they one of the production sites of the heavy elements that enable the existence of life, but their cores are also one of the densest environments we can probe, albeit indirectly. Core-collapse supernovae are also among the most spectacular and efficient neutrino factories. Detecting these neutrinos can allow us to probe physics in extreme conditions inaccessible on Earth. In this talk, I will discuss how we can prepare for the next nearby supernova neutrino detection to extract as much information as possible from the neutrino signal. I will also talk about how observing neutrinos from all the past collapses in our Universe – the diffuse supernova neutrino background - can help us better understand the supernova population and may provide hints about physics beyond the Standard Model.
  • 2:40 - 2:55 pm EDT
    The Guided Moments formalism: a new neutrino treatment
    Short Talk - 11th Floor Lecture Hall
    • Manuel Izquierdo, University of the Balearic Islands
    Abstract
    Accurate modeling of neutrino transport plays a crucial role in understanding astrophysical phenomena such as core-collapse supernovae and neutron star mergers. In this talk, I will review two popular methods for approximating the seven-dimensional Boltzmann equation: the truncated momentum formalism (M1 scheme) and Monte-Carlo (MC) algorithms. Then, I wil present the Guided Moment (GM) formalism, which combines efficiently both methods to capture accurately both optically thick and thin limits. A comparison between the three schemes (GM, M1, MC) will demonstrate the tremendous potential of the GM formalism.
  • 3:00 - 3:20 pm EDT
    Coffee Break
    11th Floor Collaborative Space
  • 3:20 - 3:50 pm EDT
    Grey Neutrino Transport in Core-Collapse Supernovae
    11th Floor Lecture Hall
    • Evan O'Connor, Stockholm University
    Abstract
    In this talk, I will share our recent work in developing a grey neutrino transport algorithm based on the M1 formalism for use in core-collapse supernovae (Andresen et al. 2024). We extensively compare with 1D and 2D simulations from various transport codes as well as our own energy-dependent M1 code. We see significant speed up compared to the energy dependent version (4-5 times faster) with only slight degradation in the neutrino signal and the dynamics. I'll also share some other recent work by the Stockholm group.
  • 4:00 - 5:00 pm EDT
    Panel Discussion I
    Panel Discussion - 11th Floor Lecture Hall
Friday, July 12, 2024
  • 9:00 - 9:30 am EDT
    TBA
    11th Floor Lecture Hall
    • Elias Most, California Institute of Technology
  • 9:40 - 10:00 am EDT
    Coffee Break
    11th Floor Collaborative Space
  • 10:00 - 10:30 am EDT
    Analytic Closures for M1 Neutrino Transport
    11th Floor Lecture Hall
    • Lena Murchikova, Northwestern University
    Abstract
    Carefully accounting for neutrino transport is an essential component of many astrophysical studies. Solving the full transport equation is too expensive for most realistic applications, especially those involving multiple spatial dimensions. Resorting to approximations is often the only viable option for obtaining solutions. One such approximation is the M1 method. It utilizes the system of the lowest two moments of the transport equation and closes the system with an ad hoc closure relation. The accuracy of the M1 solution depends on the quality of the closure. I will discuss an extensive study of these closures we carried out a few years ago by comparing the results of M1 calculations with precise Monte Carlo calculations of the radiation field around spherically-symmetric protoneutron star models. We find that no closure performs consistently better or worse than others in all cases. The level of accuracy a given closure yields depends on the matter configuration, neutrino type, and neutrino energy. Given this limitation, we concluded that the maximum entropy closure by Minerbo (1978) yields relatively accurate results in the broadest set of cases considered in this work.
  • 10:40 - 10:55 am EDT
    Control of Instability in a Vlasov-Poisson System Through External Electric Field
    Short Talk - 11th Floor Lecture Hall
    • Yukun Yue, University of Wisconsin, Madison
    Abstract
    The Vlasov-Poisson equation serves as a fundamental model for simulating plasma dynamics. Within this framework, there exist two equilibrium states that are inherently unstable, namely the Two-Stream and Bump-on-Tail instabilities. Suppressing these instabilities is often a desirable objective in numerous practical applications. This paper aims to achieve such suppression by the implementation of an external field. When minor perturbations are introduced into these equilibrium states, they have the potential to instigate rapid growth, resulting in substantial disruptions of the equilibrium. To address this challenge, we introduce two distinct strategies for applying an external field to stabilize these inherently unstable distributions. The first strategy focuses on neutralizing the electric field generated within the plasma system. This approach effectively restricts the movement of the particles in a free-drifting state. The second strategy adopts a more comprehensive approach, leveraging linear analysis to investigate various methods for the application of the external field, inclusive of the first method. We provide numerical evidence to substantiate the efficacy of these proposed methodologies.
  • 11:00 - 11:15 am EDT
    Stability of post-merger-like neutron stars
    Short Talk - 11th Floor Lecture Hall
    • Nishad Muhammed, Washington State University
    Abstract
    Binary neutron star mergers produce massive, hot, rapidly differentially rotating neutron star remnants; electromagnetic and gravitational wave signals associated with the subsequent evolution depend on the stability of these remnants. Stability of relativistic stars has previously been studied for uniform rotation and a class of differential rotation with monotonic angular velocity profiles. Stability of those equilibria to axisymmetric perturbations was found to respect a turning point criterion: along a constant angular momentum sequence, the onset of unstable stars is found at maximum density less than but close to the density of maximum mass. We test this turning point criterion for non-monotonic angular velocity profiles and non-isentropic entropy profiles, both chosen to more realistically model post-merger equilibria. Stability is assessed by evolving perturbed equilibria in 2D using the Spectral Einstein Code. We confirm the turning point theorem and determine the region of our rotation law parameter space that provides highest maximum mass for a given angular momentum.
  • 11:20 - 11:35 am EDT
    Magnetized winds from low mass BNS binaries
    Short Talk - 11th Floor Lecture Hall
    • Carlo Musolino, Goethe University Frankfurt
    Abstract
    A significant interest has emerged in assessing whether collimated and ultra-relativistic outflows can be produced by a long-lived remnant formed after a binary neutron-star (BNS) merger. To clarify some of the aspects of this process, we report the results of long-term state-of-the-art general-relativistic neutrino-magnetohydrodynamics simulations of the inspiral and merger of a magnetized BNS system. We find that after an initial phase of MRI-driven growth of the magnetic field in the torus, the field breaks out due to a Parker-type instability leading to a magnetically driven, mildly relativistic polar wind.
  • 11:40 am - 2:00 pm EDT
    Lunch/Free Time
  • 2:00 - 3:00 pm EDT
    Panel Discussion II
    Panel Discussion - 11th Floor Lecture Hall
  • 3:00 - 3:30 pm EDT
    Coffee Break
    11th Floor Collaborative Space

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