Variability in GRMHD Simulations of Sgr A∗: Implications for EHT Closure Phase Observations

Lia Medeiros, Chi Kwan Chan, Feryal Özel, Dimitrios Psaltis, Junhan Kim, Daniel P. Marrone, Aleksander Sadowski

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


Closure phases along different baseline triangles carry a large amount of information regarding the structures of the images of black holes in interferometric observations with the Event Horizon Telescope. We use long time span, high cadence, GRMHD+radiative transfer models of Sgr A∗ to investigate the expected variability of closure phases in such observations. We find that, in general, closure phases along small baseline triangles show little variability, except in the cases when one of the triangle vertices crosses one of the small regions of low visibility amplitude. The closure phase variability increases with the size of the baseline triangle, as larger baselines probe the small-scale structures of the images, which are highly variable. On average, the funnel-dominated MAD models show less closure phase variability than the disk-dominated SANE models, even in the large baseline triangles, because the images from the latter are more sensitive to the turbulence in the accretion flow. Our results suggest that image reconstruction techniques need to explicitly take into account the closure phase variability, especially if the quality and quantity of data allow for a detailed characterization of the nature of variability. This also implies that, if image reconstruction techniques that rely on the assumption of a static image are utilized, regions of the u-v space that show a high level of variability will need to be identified and excised.

Original languageEnglish (US)
Article number35
JournalAstrophysical Journal
Issue number1
StatePublished - Jul 20 2017


  • Galaxy: center
  • accretion accretion disks
  • black hole physics
  • radiative transfer

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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