First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole

The Event Horizon Telescope Collaboration

Sasada Mahito

The Astrophysical Journal Letters

We present measurements of the properties of the central radio source in M87 using Event Horizon Telescope data obtained during the 2017 campaign. We develop and fit geometric crescent models (asymmetric rings with interior brightness depressions) using two independent sampling algorithms that consider distinct representations of the visibility data. We show that the crescent family of models is statistically preferred over other comparably complex geometric models that we explore. We calibrate the geometric model parameters using general relativistic magnetohydrodynamic (GRMHD) models of the emission region and estimate physical properties of the source. We further fit images generated from GRMHD models directly to the data. We compare the derived emission region and black hole parameters from these analyses with those recovered from reconstructed images. There is a remarkable consistency among all methods and data sets. We find that >50% of the total flux at arcsecond scales comes from near the horizon, and that the emission is dramatically suppressed interior to this region by a factor >10, providing direct evidence of the predicted shadow of a black hole. Across all methods, we measure a crescent diameter of 42 ± 3 μas and constrain its fractional width to be <0.5. Associating the crescent feature with the emission surrounding the black hole shadow, we infer an angular gravitational radius of GM/Dc^2 = 3.8 ± 0.4 μas. Folding in a distance measurement of 16.8^+0.8_-0.7 Mpc gives a black hole mass of M = 6.5 ± 0.2∣_stat ± 0.7∣_sys × 10⁹M⊙. This measurement from lensed emission near the event horizon is consistent with the presence of a central Kerr black hole, as predicted by the general theory of relativity.

black hole physics

galaxies: individual (M87)

gravitation

techniques: high angular resolution

techniques: interferometric

eng

The American Astronomical Society

© 2019. The American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

[ISSN] 2041-8205

[ISSN] 2041-8213

[DOI] 10.3847/2041-8213/ab1141

[DOI] https://doi.org/10.3847/2041-8213/ab1141