Session Y01: New Vistas in the Simulation of Matter in Strongly Gravitating Systems

Live

Recent years have seen remarkable successes in novel observational techniques for studying strongly gravitating systems, including plasma around black holes and merging compact objects. The fidelity of data now available and expected in the near future demands dramatic advances in modeling, but the environments around black holes and neutron stars include a broad range of conditions that present numerous challenges for numerical simulation. Like many complex systems, these phenomena are also strongly multi-scale and multi-physics. Among the most acute challenges, adequate treatments of photon and/or neutrino transport and coupling to matter are critical in determining the properties of these systems and unambiguously interpreting observational data. In this talk, I will describe recent advances in modeling capability, particularly associated with radiation, and applications to several relativistic systems. I will also describe a novel method for radiation transport in these environments that will substantially broaden the applicability of our codes. Finally, I will describe ongoing development of a new highly scalable, performance portable code for relativistic astrophysics that promises to unveil new vistas on strongly gravitating systems.   

Live

Accreting supermassive binary black holes are key multi-messenger sources for LISA, yet are challenging to simulate realistically as solving the radiation magnetohydrodynamics (MHD) equations over the full dynamic spatio-temporal range of the problem is computationally infeasible at present. We will provide a brief summary of the the progress made in the field to understand these systems theoretically and what new directions groups are pursuing. We will also report on our collaboration's progress to simulate these systems using general relativistic MHD and dynamic GR. In order to cover a larger temporal range in one set of simulations, we constrain our view to the circumbinary disk region and measure how the binary mass ratio, accretion disk size, and black hole spin have on the structure and variability of the accretion flow. We particularly emphasize how these parameters influence the overdensity feature, which orbits the binary near the edge of the cavity, since it is responsible for most of the electromagnetic emission's variability and variability is a key signature of a system being a binary. Extending to smaller length scales, we will report on simulations following accretion all the down to the event horizons so that we can begin to investigate how black hole spin affects mini-disk dynamics, accretion rate, and jet power. The novel computational methods enabling inclusion of the black holes in the domain, including multi-patch methods, will be described.   

Live

The era of gravitational-wave and multi-messenger astronomy sheds light on the astrophysics of black holes and neutron star binaries and also allows for unique probes of fundamental physics. I will discuss recent results on how neutron-star mergers and other strongly gravitating systems of prime interest in time-domain astronomy, such as collapsars, give rise to the formation of heavy elements in the universe. In particular, I will discuss simulation results at the interface of numerical relativity, neutrino physics (including oscillations), and nuclear physics, and highlight their implications for multi-messenger astrophysics and chemical evolution of galaxies.