Hybrid GRMHD and Force-Free Simulations of Black Hole Accretion
Fuente:
arXiv
Saved in:
| Main Author: | |
|---|---|
| Format: | Preprint |
| Published: |
2024
|
| Subjects: | |
| Online Access: | |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1866917722043973632 |
|---|---|
| author | Chael, Andrew |
| author_facet | Chael, Andrew |
| contents | We present a new approach for stably evolving general relativistic magnetohydrodynamic (GRMHD) simulations in regions where the magnetization $σ=b^2/ρc^2$ becomes large. GRMHD codes typically struggle to evolve plasma above $σ\approx100$ in simulations of black hole accretion. To ensure stability, GRMHD codes will inject mass density artificially to the simulation as necessary to keep the magnetization below a ceiling value $σ_{\rm max}$. We propose an alternative approach where the simulation transitions to solving the equations of general relativistic force-free electrodynamics (GRFFE) above a magnetization $σ_{\rm trans}$. We augment the GRFFE equations in the highly magnetized region with approximate equations to evolve the decoupled field-parallel velocity, plasma energy density, and plasma mass density. Our hybrid scheme is explicit and easily added to the framework of standard-volume GRMHD codes. We present a variety of tests of our method, implemented in the GRMHD code KORAL, and we show first results from a 3D hybrid GRMHD+GRFFE simulation of a magnetically arrested disc (MAD) around a spinning black hole. Our hybrid MAD simulation closely matches the average properties of a standard GRMHD MAD simulation with the same initial conditions in low magnetization regions, but it achieves a magnetization $σ\approx10^6$ in the evacuated jet funnel. We present simulated horizon-scale images of both simulations at 230 GHz with the black hole mass and accretion rate matched to M87*. Images from the hybrid simulation are less affected by the choice of magnetization cutoff $σ_{\rm cut}$ imposed in radiative transfer than images from the standard GRMHD simulation. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2404_01471 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Hybrid GRMHD and Force-Free Simulations of Black Hole Accretion Chael, Andrew High Energy Astrophysical Phenomena We present a new approach for stably evolving general relativistic magnetohydrodynamic (GRMHD) simulations in regions where the magnetization $σ=b^2/ρc^2$ becomes large. GRMHD codes typically struggle to evolve plasma above $σ\approx100$ in simulations of black hole accretion. To ensure stability, GRMHD codes will inject mass density artificially to the simulation as necessary to keep the magnetization below a ceiling value $σ_{\rm max}$. We propose an alternative approach where the simulation transitions to solving the equations of general relativistic force-free electrodynamics (GRFFE) above a magnetization $σ_{\rm trans}$. We augment the GRFFE equations in the highly magnetized region with approximate equations to evolve the decoupled field-parallel velocity, plasma energy density, and plasma mass density. Our hybrid scheme is explicit and easily added to the framework of standard-volume GRMHD codes. We present a variety of tests of our method, implemented in the GRMHD code KORAL, and we show first results from a 3D hybrid GRMHD+GRFFE simulation of a magnetically arrested disc (MAD) around a spinning black hole. Our hybrid MAD simulation closely matches the average properties of a standard GRMHD MAD simulation with the same initial conditions in low magnetization regions, but it achieves a magnetization $σ\approx10^6$ in the evacuated jet funnel. We present simulated horizon-scale images of both simulations at 230 GHz with the black hole mass and accretion rate matched to M87*. Images from the hybrid simulation are less affected by the choice of magnetization cutoff $σ_{\rm cut}$ imposed in radiative transfer than images from the standard GRMHD simulation. |
| title | Hybrid GRMHD and Force-Free Simulations of Black Hole Accretion |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2404.01471 |