Relative depolarization of the black hole photon ring in GRMHD models of Sgr A* and M87*

Abstract

Using general relativistic magnetohydrodynamic simulations of accreting black holes, we show that a suitable subtraction of the linear polarization per pixel from total intensity images can enhance the photon ring features. We find that the photon ring is typically a factor of $\simeq 2$ less polarized than the rest of the image. This is due to a combination of plasma and general relativistic effects, as well as magnetic turbulence. When there are no other persistently depolarized image features, adding the subtracted residuals over time results in a sharp image of the photon ring. We show that the method works well for sample, viable GRMHD models of Sgr A* and M87*, where measurements of the photon ring properties would provide new measurements of black hole mass and spin, and potentially allow for tests of the "no-hair" theorem of general relativity.

13 pages, 12 figures, accepted for publication in MNRAS

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• Polarimetric signatures of hot spots in black hole accretion flows
• Polarimetric signatures of the photon ring of a black hole that is pierced by a cosmic axion string
• Polarized image of an equatorial emitting ring around a 4D Gauss-Bonnet black hole
• Polarization images of accretion flow around supermassive black holes: imprints of toroidal field structure
• Birefringence Tomography for Axion Cloud
• Probing Plasma Physics with Spectral Index Maps of Accreting Black Holes on Event Horizon Scales
• Survey of Non-thermal Electron around Supermassive Black Holes through Polarization Flips
• Photon ring polarimetry with next-generation black hole imaging I. M87*
• Prospects for ray-tracing light intensity and polarization in models of accreting compact objects using a GPU
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• Photon Ring Symmetries in Simulated Linear Polarization Images of Messier 87*
• Orbit design for mitigating interstellar scattering effects in Earth-space VLBI observations of Sgr A*