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Characterizing Power Spectra of GRMHD Simulations using the Taylor Frozen Hypothesis

Presentation #117.13 in the session Time-Domain Astrophysics.

Published onJul 01, 2023
Characterizing Power Spectra of GRMHD Simulations using the Taylor Frozen Hypothesis

The Event Horizon Telescope (EHT) recently published the first resolved images of the Galactic Center black hole (Sagittarius A*, Sgr A*). Comparisons between EHT observations and current state-of-the-art general relativistic magnetohydrodynamic (GRMHD) simulations indicate that the simulations may be more variable than the data, demonstrating the remarkable constraining power of EHT observations. Given the EHT observations, our goal is to characterize the spatial power spectrum of fluctuations of MHD turbulence in various high-resolution, long-time span GRMHD simulations. We explore the utility of the Taylor frozen hypothesis for this purpose which allows us to convert temporal power spectra into spatial power spectra, given a few assumptions. We carefully test the validity of this approximation for GRMHD simulations. Using outputs from the simulation code, KORAL, we explore models with strong and ordered magnetic fields (MAD, magnetically arrested disks) and weak and disordered magnetic fields (SANE, Standard and Normal Evolution) of varying black hole spin (prograde and retrograde). Large libraries of GRMHD simulations often are computationally expensive, time intensive and make several assumptions about plasma physics. Analytic accretion models can be used to explore a broader range of parameters instead; however, comparing the smooth flows produced by these models to the complex flow morphologies seen in the simulations is challenging. We explore the feasibility of creating a parametric model for variability. Using physically motivated power spectra from the simulations, we perturb analytic accretion flows and perform radiative transfer simulations through the perturbed flows. This method provides a fundamentally new approach to efficiently creating large libraries of images probing different turbulence realizations while allowing for a more expansive parameter space.

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