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

A. Jiménez-Rosales*, J. Dexter*, S. M. Ressler, A. Tchekhovskoy, M. Bauböck, Y. Dallilar, P. T. de Zeeuw, A. Drescher, F. Eisenhauer, S. von Fellenberg, F. Gao, R. Genzel, S. Gillessen, M. Habibi, T. Ott, J. Stadler, O. Straub, F. Widmann

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


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 feature. We find that the photon ring is typically a factor of ≃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.

Original languageEnglish (US)
Pages (from-to)4563-4575
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - May 1 2021


  • Accretion
  • Accretion discs
  • Black hole physics
  • MHD
  • Polarization
  • Radiative transfer

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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