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Title: Reading the envelope structure of a red supergiant from supernova early emission: the case of SN 2023ixf
Title: Reading the envelope structure of a red supergiant from supernova early emission: the case of SN 2023ixf
Speaker: Ehud Nakar (Tel Aviv University)
Abstract: TBD
August 14: Understanding pulsars and their plasma with radio waves
August 14: Understanding pulsars and their plasma with radio waves
Speaker: Ryan Craft (Curtin University)
Abstract: Since the discovery of pulsars in 1967 the mechanism which generates their coherent radio emission has remained elusive. With recent developments driven by Force Free and Particle-In-Cell simulations of the pulsar plasma, simulations have been able to demonstrate from first principles the emergence of coherent radio emission from the magnetised plasma. Even with this great advancement, simulations have yet to reproduce the wide variety of unusual time and frequency dependent pulsar phenomena. This talk will give a broad overview of those phenomena from data I have collected from different radio instruments, and show you our strategy for testing the modern emission theory against state-of-the-art telescope data.
June 26: Breaking Behaviors of Neutron Star Crusts
June 26: Breaking Behaviors of Neutron Star Crusts
Speaker: Nevin Smith (Illinois State University)
Speaker: Nevin Smith (Illinois State University)
Abstract: Magnetar transients are thought to be caused by the breaking of neutron star crusts. Beyond the linear-elastic regime, the breaking behavior of the crust is not understood. We perform first-principles molecular dynamics simulations that study the break and post-break behavior of the crust. Additionally, we develop a new method to include magnetic fields in molecular dynamic simulations.
Abstract: Magnetar transients are thought to be caused by the breaking of neutron star crusts. Beyond the linear-elastic regime, the breaking behavior of the crust is not understood. We perform first-principles molecular dynamics simulations that study the break and post-break behavior of the crust. Additionally, we develop a new method to include magnetic fields in molecular dynamic simulations.
June 12: A Tourist’s Guide to Superconducting MHD
Speaker: Robert Ewart (Princeton)
Abstract: TBA
June 4: Cosmic rays in cosmological simulations - bridging scales
June 12: A Tourist’s Guide to Superconducting MHD
Speaker: Robert Ewart (Princeton)
Abstract: TBA
June 4: Cosmic rays in cosmological simulations - bridging scales
Speaker: Ludwig Boess (UChicago)
Abstract: Galaxy clusters and their role in the large-scale structure of the Universe, the cosmic web, have been studied extensively through observations and simulations. However, many of the high-energy process that happen in these structures still elude observations and pose significant challenges for simulations of large-scale structure formation. Most notably, the accretion of matter onto the cosmic web and the collisions of galaxy clusters embedded in it dissipate a large fraction of their gravitational energy in the form of shocks. These shocks heat the intra-cluster medium to keV energies and can accelerate protons and electrons to relativistic velocities. Non-thermal emission from relativistic electrons gives insight into the strength and morphology of intra-cluster magnetic fields, as well as providing powerful tracers of structure formation shocks. Large-scale simulations which include the effects of CRs have been difficult to achieve since the difference between the scale where CRs interact with the thermal gas and the resolution of these simulations spans more than 20 orders of magnitude. PIC and hybrid simulations are the most successful tools to study cosmic ray acceleration at astrophysical shocks. However, most of these simulations are limited to 1D/2D due to computational constraints. In this talk, I will give an overview of how we work to improve the modeling of CRs in large-scale simulations of cosmological structure formation. I will introduce the spectral CR model we use to evolve CR populations on-the-fly in our simulations and its application to simulations of the local Universe and present improvements to the PIC code entity which we plan to use for 3D PIC simulations of ICM shocks.
May 6: Vortex Dynamics in the Neutron Star Inner Crust
Abstract: Galaxy clusters and their role in the large-scale structure of the Universe, the cosmic web, have been studied extensively through observations and simulations. However, many of the high-energy process that happen in these structures still elude observations and pose significant challenges for simulations of large-scale structure formation. Most notably, the accretion of matter onto the cosmic web and the collisions of galaxy clusters embedded in it dissipate a large fraction of their gravitational energy in the form of shocks. These shocks heat the intra-cluster medium to keV energies and can accelerate protons and electrons to relativistic velocities. Non-thermal emission from relativistic electrons gives insight into the strength and morphology of intra-cluster magnetic fields, as well as providing powerful tracers of structure formation shocks. Large-scale simulations which include the effects of CRs have been difficult to achieve since the difference between the scale where CRs interact with the thermal gas and the resolution of these simulations spans more than 20 orders of magnitude. PIC and hybrid simulations are the most successful tools to study cosmic ray acceleration at astrophysical shocks. However, most of these simulations are limited to 1D/2D due to computational constraints. In this talk, I will give an overview of how we work to improve the modeling of CRs in large-scale simulations of cosmological structure formation. I will introduce the spectral CR model we use to evolve CR populations on-the-fly in our simulations and its application to simulations of the local Universe and present improvements to the PIC code entity which we plan to use for 3D PIC simulations of ICM shocks.
May 6: Vortex Dynamics in the Neutron Star Inner Crust
Speaker: Xin Sheng (Columbia University)
Abstract: Neutron star glitches are hypothesized to result from the sudden coupling between the star's crust and its inner superfluid. To elucidate this mechanism, we perform direct three-dimensional simulations of superfluid vortex motion within the inner crust, accounting for interactions of the vortex and the nuclear lattice. Our results provide a critical link between microscopic vortex pinning and the macroscopic glitch events observed in pulsars. Specifically, we demonstrate that massive vortex unpinning can be triggered by two mechanisms: lattice shearing during starquakes and vortex avalanches.
April 24: A Discontinuous Galerkin Scheme for the General Relativistic Vlasov-Maxwell-BGK System
Abstract: Neutron star glitches are hypothesized to result from the sudden coupling between the star's crust and its inner superfluid. To elucidate this mechanism, we perform direct three-dimensional simulations of superfluid vortex motion within the inner crust, accounting for interactions of the vortex and the nuclear lattice. Our results provide a critical link between microscopic vortex pinning and the macroscopic glitch events observed in pulsars. Specifically, we demonstrate that massive vortex unpinning can be triggered by two mechanisms: lattice shearing during starquakes and vortex avalanches.
April 24: A Discontinuous Galerkin Scheme for the General Relativistic Vlasov-Maxwell-BGK System
Speaker: Grant R Johnson (PPPL)
Abstract: In this seminar, I will present a continuum kinetic framework for plasmas in curved spacetime based on a discontinuous Galerkin (DG) representation of the general relativistic Vlasov-Maxwell-BGK system. The formulation is built on a non-canonical Hamiltonian structure that preserves discrete conservation laws. This is combined with a local tetrad representation that provides an efficient phase-space discretization and straightforward coupling to local processes like collisions, radiation, and pair production. To demonstrate the successful implementation of this approach, I will present benchmarks from the current implementation in Gkeyll, including tests of geodesic motion, verification of discrete conservation laws, convergence to hydrodynamics in the highly collisional limit, and vacuum solutions to the Maxwell solver. I will conclude by looking ahead to the self-consistent coupling of the fields to the kinetic system and the unique applications which will be possible with this continuum phase space method.
April 8: Strongly magnetised ion–electron Relativistic Reconnection with Guide Field
April 8: Strongly magnetised ion–electron Relativistic Reconnection with Guide Field
Speaker: Pranab Deka (from KU Leuven)
Abstract: Relativistic magnetic reconnection is a fundamental mechanism of energy dissipation in magnetised astrophysical environments, including black hole coronae, pulsar winds, and relativistic jets. We present fully kinetic three-dimensional ion–electron simulations that extend recent studies of relativistic reconnection by scanning guide-field strength across strongly magnetised regimes. At low magnetisation, increasing guide field strength delays nonlinear disruption of the current sheet and strongly suppresses magnetic energy dissipation. The zero-guide-field case exhibits rapid collapse of the reconnecting field and efficient nonthermal electron acceleration, while strong guide fields stabilise the layer and significantly reduce high-energy tail formation. At higher magnetisations, reconnection remains rapid but the guide field regulates species energy partition between species. Stronger guide fields reduce the fraction of magnetic energy converted into nonthermal electrons and favour enhanced ion heating with softer electron spectra. These results demonstrate that the guide field strongly regulates three-dimensional plasma instability development, dissipation efficiency, and species-dependent particle acceleration in ion-electron plasmas.
March 20: A Modern Perspective on Pair Plasma Creation in Neutron Star Magnetospheres
Abstract: Relativistic magnetic reconnection is a fundamental mechanism of energy dissipation in magnetised astrophysical environments, including black hole coronae, pulsar winds, and relativistic jets. We present fully kinetic three-dimensional ion–electron simulations that extend recent studies of relativistic reconnection by scanning guide-field strength across strongly magnetised regimes. At low magnetisation, increasing guide field strength delays nonlinear disruption of the current sheet and strongly suppresses magnetic energy dissipation. The zero-guide-field case exhibits rapid collapse of the reconnecting field and efficient nonthermal electron acceleration, while strong guide fields stabilise the layer and significantly reduce high-energy tail formation. At higher magnetisations, reconnection remains rapid but the guide field regulates species energy partition between species. Stronger guide fields reduce the fraction of magnetic energy converted into nonthermal electrons and favour enhanced ion heating with softer electron spectra. These results demonstrate that the guide field strongly regulates three-dimensional plasma instability development, dissipation efficiency, and species-dependent particle acceleration in ion-electron plasmas.
March 20: A Modern Perspective on Pair Plasma Creation in Neutron Star Magnetospheres
Speaker: Andrey Timokhin (Janusz Gil Institute of Astronomy, University of Zielona Gora)
Abstract: The magnetospheres of pulsars are filled with dense electron–positron plasma that is responsible for essentially all their non-thermal emission. This plasma is believed to be created in electromagnetically driven electron–positron pair cascades in their polar caps, triggered by intermittent strong electric fields that accelerate charged particles to ultrarelativistic energies. These particles emit high-energy photons, which subsequently decay into electron–positron pairs. Although pair creation in neutron star magnetospheres has been studied extensively over the past six decades, only recently have we been able to model this process in a truly self-consistent way, thanks to modern numerical techniques and advances in computer hardware. The results of these simulations have already shown that several standard features of earlier models are incorrect. For example, pair discharges appear to be inherently intermittent, there are no sparks in pulsar polar caps, and radio emission may be generated directly by the discharges themselves. In this talk, I will provide an overview of the most recent developments in this field and present possible solutions to the long-standing and notoriously difficult problem of the origin of pulsar radio emission.
March 13: Collisionless Self-Interacting Dark Matter
Speaker: Ani Prabhu (PCTS)
Abstract: TBA
March 6: Large-scale dynamos driven by shear-flow-induced jets
March 6: Large-scale dynamos driven by shear-flow-induced jets
Speaker: Bindesh Tripathi (Columbia University)
Abstract: The origin of cosmic magnetic fields remains an open problem in astrophysics. In 1955, Eugene Parker proposed a mean-field dynamo theory by parameterizing the effects of small-scale turbulence. Although this framework successfully reproduces observed large-scale magnetic fields, it relies on parameters that are difficult to constrain from first principles. Here, by analyzing an unstable, driven shear flow, we develop analytic theory and perform three-dimensional simulations of turbulence with up to 4,096 × 4,096 × 8,192 grid points. The simulations demonstrate ab initio generation of quasi-periodic, large-scale magnetic fields. The generation operates via the mean-vorticity effect—an additional mean-field dynamo process postulated in 1990—and is driven by robust, large-scale, three-dimensional, nonlinear jets. Predictions from the jet-driven dynamo are confirmed using data from a shear-driven laboratory dynamo experiment. This dynamo mechanism applies to a variety of astrophysical systems, including binary neutron star mergers, where it can produce some of the strongest magnetic fields in the Universe, providing signals for multi-messenger astronomy.
March 6: Modelling Magnetic Dissipation in Magnetized Magnetospheres
Speaker: Michael Grehan (University of Toronto)
Abstract: Highly magnetized neutron star and black hole magnetospheres can convert magnetic energy into high-energy emission through shocks and reconnection. In this talk, I present recent relativistic MHD simulations of two such processes. First, I discuss “monster shocks” — ultra-relativistic magnetized shocks that form when waves launched from a neutron star steepen in a magnetically dominated magnetosphere. Our simulations confirm analytical predictions for equatorial shocks, extend them to oblique geometries, and show that additional magnetospheric modes can fragment the shock front, reduce magnetization, and intermittently generate secondary shocks. Second, I present a kinetic-motivated effective resistivity for relativistic resistive MHD that links the reconnection electric field to charge-starved current densities. This approach reproduces the reconnection rates seen in kinetic models, both in local current sheets and global black hole magnetospheres, and has direct applications to pulsar simulations.
February 20: Tidal Disruption of a Magnetized Star by an Intermediate-Mass Black Hole
February 20: Tidal Disruption of a Magnetized Star by an Intermediate-Mass Black Hole
Speaker: Omer Bromberg (Tel Aviv University)
Abstract: TBA
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