Events at Physics

<< Summer 2023 Fall 2023 Spring 2024 >>
Subscribe your calendar or receive email announcements of events

Events on Thursday, October 5th, 2023

Astronomy Colloquium
On the Comparison of AGN with GRMHD Simulations: Sgr A* and M87
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
Speaker: Richard Anantua, University of Texas at San Antonio
Abstract: With the advent of the sub-mm imaging of two distinct black hole shadows in 2019 and 2022 by the Event Horizon Telescope, we are now in position to infer the physical properties of such systems using phenomenological models. Models of magnetized plasma in the jet (or outflow)/accretion flow/black hole (JAB) system Sagittarius A* based on turbulent heating and deviations from the equipartition of particle and magnetic energies are input into a High Accuracy Relativistic Magnetohydrodynamics (HARM) simulation. Spectra, movies and light curves simulating hourly timescales show that these models aggregate into four quasi-stationary types: 1.) thin, asymmetric photon ring with best fit spectrum; 2.) coronal boundary layer with thin photon ring and steep spectrum; 3.) thick photon ring with flat spectrum; and 4.) extended outflow with low frequency spectral knee. For M87, a self-similar, stationary, axisymmetric jet model based on a force-free flow in a HARM jet simulation is used to generate Stokes maps at Very Long Baseline Array (VLBA, 43 GHz) and Event Horizon Telescope (EHT, 230 GHz) scales. The model varies plasma content from ionic (e-p) to pair (e-e+). Emission at the observed frequency is assumed to be synchrotron radiation from electrons and positrons, whose pressure is set to be constant fractions of the local magnetic pressure. The cleanest observational signature in the Stokes maps is the vanishing of circular polarization for increasing positron content. Positrons are also incorporated into the general relativistic ray tracer IPOLE to display positron effects on general relativistic magnetohydrodynamic simulations, showing stark differences in polarization signatures between standard and normal evolution (SANE) and magnetically arrested disk (MAD) accretion modes due to Faraday effects. The inclusion of electrons, positrons and protons in our radiative transfer pipeline thus provides a powerful probe of the composition of JAB systems
Host: Ke Zhang
Add this event to your calendar