Origin of the ring ellipticity in the black hole images of M87*

Abstract

We investigate the origin of the elliptical ring structure observed in the images of the supermassive black hole M87*, aiming to disentangle contributions from gravitational, astrophysical, and imaging effects. Leveraging the enhanced capabilities of the Event Horizon Telescope (EHT) 2018 array, including improved $(u,v)$-coverage from the Greenland Telescope, we measure the ring's ellipticity using five independent imaging methods, obtaining a consistent average value of $\tau =0.08_{-0.02}^{+0.03}$ with a position angle $\xi =50.1_{-7.6}^{+6.2}$ degrees. To interpret this measurement, we compare against General Relativistic Magnetohydrodynamic (GRMHD) simulations spanning a wide range of physical parameters including thermal or non-thermal electron distribution function, spins, and ion-to-electron temperature ratios in both low and high-density regions. We find no statistically significant correlation between spin and ellipticity in GRMHD images. Instead, we identify a correlation between ellipticity and the fraction of non-ring emission, particularly in non-thermal models and models with higher jet emission. These results indicate that the ellipticity measured from the \m87 emission structure is consistent with that expected from simulations of turbulent accretion flows around black holes, where it is dominated by astrophysical effects rather than gravitational ones. Future high-resolution imaging, including space very long baseline interferometry and long-term monitoring, will be essential to isolate gravitational signatures from astrophysical effects.

18 pages, 13 figures

References in corpus (25)

• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
• First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
• First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
• First M87 Event Horizon Telescope Results. II. Array and Instrumentation
• First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
• Black Hole Shadows, Photon Rings, and Lensing Rings
• Kinematics of the jet in M87 on scales of 100 -- 1000 Schwarzschild radii
• Lensing by Kerr Black Holes
• Observing the Inner Shadow of a Black Hole: A Direct View of the Event Horizon
• Imaging the Schwarzschild-radius-scale Structure of M87 with the Event Horizon Telescope using Sparse Modeling
• Key Science Goals for the Next-Generation Event Horizon Telescope
• Super-resolution Full Polarimetric Imaging for Radio Interferometry with Sparse Modeling
• State-of-the-art energetic and morphological modelling of the launching site of the M87 jet
• Simulations of imaging the event horizon of Sagittarius A* from space
• Black Hole Images as Tests of General Relativity: Effects of Spacetime Geometry
• Reference Array and Design Consideration for the next-generation Event Horizon Telescope
• Monitoring the Morphology of M87* in 2009-2017 with the Event Horizon Telescope
• Hybrid Very Long Baseline Interferometry Imaging and Modeling with Themis
• Iharm3D: Vectorized General Relativistic Magnetohydrodynamics
• Variational Image Feature Extraction for the Event Horizon Telescope
• Measuring the Ellipticity of M 87* Images
• Polarimetric Geometric Modeling for mm-VLBI Observations of Black Holes
• Imaging a ring-like structure and the extended jet of M87 at 86 GHz
• Monitoring the Size and Flux Density of Sgr A* during the Active State in 2019 with East Asian VLBI Network

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