12:35 PM - 01:20 PM (45 min)

Lighning talk session I

1. A new primitive variable recovery scheme in GRMHD code Spritz

12:35 PM – 12:44 PM

Jay Vijay Kalinani (University of Padova, Italy) (recording)

General relativistic magnetohydrodynamic (GRMHD) simulations are an indispensable tool to obtain a detailed physical understanding of binary neutron star (BNS) mergers. Flux-preserving GRMHD codes numerically evolve a set of conservative equations based on ‘conserved’ variables which then need to be converted back to the ‘primitive’ physical variables. The corresponding conservative-to- primitive (c2p) recovery procedure is a crucial aspect at the core of any GRMHD code. In this talk, I will discuss a completely new c2p recovery scheme for ideal MHD. Using both stand-alone tests and by performing demanding three-dimensional GRMHD tests, we have demonstrated robustness, accuracy, and efficiency over the whole relevant parameter space. This includes the critical case of very strong magnetizations. I will also talk about technical aspects of implementing the scheme in our new GRMHD code Spritz, such as the requirements for the EOS framework.

2. Neutron Star wind simulations

12:44 PM – 12:53 PM

Dhruv Desai (Columbia University)

I will present results of neutrino-driven winds using an M0 scheme for neutrino transport and a tabulated EOS. I will compare wind results (mass flow rate, composition, entropy) for a non-rotating and rigidly-rotating case. I will briefly discuss implications for heavy element synthesis via r-process.

3. Binary neutron star mergers of quark matter based nuclear equations of state

12:53 PM – 01:02 PM

Atul Kedia (University of Notre Dame) (slides) (recording)

With recent observations of gravitational wave signals from binary neutron star(BNS) mergers and observations by NICER, the nuclear equation of state(EoS) is becoming increasingly testable by numerical simulations. Numerous simulations currently exist exploring the equations of state at different density regimes for the constituent neutron stars. In this work we perform full GR three-dimensional hydrodynamics simulations of BNS mergers for parameterized EoSs based on quark matter at the highest nuclear densities. We construct our initial data using Lorene followed by simulating the merger with Einstein Toolkit. The goal of this study is to extract the effects on the observed GW waveform as the merger happens caused by quark matter.

4. Neutron star simulations in screened modified gravity

01:02 PM – 01:11 PM

Alexandru Dima (SISSA) (recording)

Screening mechanisms in modified gravity are devised to suppress deviations from General Relativity in typical astrophysical scenarios, allowing these theories to avoid constraints coming from weak field observations. However, only few work has been done to explore the validity of screening mechanisms in extreme regimes, such as in the interior of neutron stars. In this talk I will briefly present results from numerical simulations of chameleon-(un)screened neutron stars and discuss the strong signatures allowed when the screening mechanism fails.

5. Neutrino Fast Flavor Conversions in Neutron-star Post-Merger Accretion Disks

01:11 PM – 01:20 PM

Xinyu Li (CITA/PI) (slides) (recording)

A compact accretion disk may be formed in the merger of two neutron stars or of a neutron star and a stellar-mass black hole. Outflows from such accretion disks have been identified as a major site of rapid neutron-capture (r-process) nucleosynthesis and as the source of `red’ kilonova emission following the first observed neutron-star merger GW170817. We present long-term general-relativistic radiation magnetohydrodynamic simulations of a typical post-merger accretion disk at initial accretion rates of 1Msun/s over 400ms post-merger. We include neutrino radiation transport that accounts for effects of neutrino fast flavor conversions dynamically. We find ubiquitous flavor oscillations that result in a significantly more neutron-rich outflow, providing lanthanide and 3rd-peak r-process abundances similar to solar abundances. This provides strong evidence that post-merger accretion disks are a major production site of heavy r-process elements. A similar flavor effect may allow for increased lanthanide production in collapsars.