Rotation in Event Horizon Telescope Movies

Nicholas S. Conroy, Michi Bauböck, Vedant Dhruv, Daeyoung Lee, Avery E. Broderick, Chi Kwan Chan, Boris Georgiev, Abhishek V. Joshi, Ben Prather, Charles F. Gammie

Research output: Contribution to journalArticlepeer-review


The Event Horizon Telescope (EHT) has produced images of M87* and Sagittarius A*, and will soon produce time sequences of images, or movies. In anticipation of this, we describe a technique to measure the rotation rate, or pattern speed Ωp , from movies using an autocorrelation technique. We validate the technique on Gaussian random field models with a known rotation rate and apply it to a library of synthetic images of Sgr A* based on general relativistic magnetohydrodynamics simulations. We predict that EHT movies will have Ωp ≈ 1° per GMc −3, which is of order 15% of the Keplerian orbital frequency in the emitting region. We can plausibly attribute the slow rotation seen in our models to the pattern speed of inward-propagating spiral shocks. We also find that Ωp depends strongly on inclination. Application of this technique will enable us to compare future EHT movies with the clockwise rotation of Sgr A* seen in near-infrared flares by GRAVITY. Pattern speed analysis of future EHT observations of M87* and Sgr A* may also provide novel constraints on black hole inclination and spin, as well as an independent measurement of black hole mass.

Original languageEnglish (US)
Article number46
JournalAstrophysical Journal
Issue number1
StatePublished - Jul 1 2023

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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