First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole (1906.11243v1)

Abstract: 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 micro-as 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/Dc2 = 3.8+/- 0.4 micro-as. 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) 10^9 Msun. 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.

• The paper presents a novel EHT analysis that images M87’s black hole shadow and measures a crescent diameter of 42 ± 3 μas.
• It employs dual sampling algorithms and GRMHD model calibration to robustly estimate the surrounding emission parameters.
• The study confirms a Kerr black hole with a mass of (6.5 ± 0.2stat ± 0.7sys) × 10^9 M⊙, reinforcing predictions of general relativity.

Analysis of M87's Central Black Hole via EHT Data

The investigation of supermassive black holes (SMBHs) has reached a new milestone with the Event Horizon Telescope (EHT) observations of the elliptical galaxy M87, situated in the Virgo Cluster. This paper, published in The Astrophysical Journal Letters, provides a comprehensive analysis of the SMBH at the center of M87, leveraging data obtained from the EHT during the 2017 observational campaign. The paper is a pivotal effort in understanding the properties and implications of black hole shadows and their surrounding emission structures.

Methodology and Measurement Techniques

The research employs an advanced methodology involving geometric crescent models, also referred to as asymmetric rings with interior brightness depressions. The approach features two independent sampling algorithms that scrutinize distinct representations of visibility data captured by the EHT. Through a meticulous calibration process using general relativistic magnetohydrodynamic (GRMHD) models, the paper extracted physical parameters of the black hole's emission region. Furthermore, the work entailed fitting GRMHD-generated images directly to the data, ensuring robustness in the derived black hole parameters.

Observational Results and Analytical Consistency

Remarkable consistency was observed across various analytical methods and data sets. It was found that over 50% of the total flux at arcsecond scales originates near the event horizon, with emission notably suppressed in the region interior to the photon ring— a signature of a black hole shadow. The consistent measurement of a crescent diameter of 42 ± 3 μas, along with a fractional width constrained to be less than 0.5, substantiates the existence of M87's black hole shadow.

The paper also determined an angular gravitational radius GM/Dc = 3.8 ± 0.4 μas based on the association between the crescent feature and the emission circumventing the black hole shadow. Incorporating an estimated distance of 16.8 -0.7Mpc, the mass of the black hole was calculated to be M = (6.5 ± 0.2stat 0.7sys) × 10^9 M_e. This mass estimation, derived from lensed near-horizon emission, corroborates the presence of a central Kerr black hole, a key prediction of general relativity.

Implications and Future Directions

This research presents significant implications for theoretical and practical black hole physics. The successful imaging and analysis of M87's black hole shadow confirm predictions of general relativity, particularly the nature of the Kerr metric describing rotating black holes. Moreover, this work lays the groundwork for future research into the dynamic properties and environment of SMBHs, advancing the precision of black hole mass and distance estimates.

The potential for future developments in high angular resolution and interferometric techniques is notable. The methodology could be extended to other galaxies with prominent SMBHs, possibly uncovering variations in black hole properties related to spin, inclination, or mass accretion processes. The considerable alignment among different data interpretation models highlights the robustness of the methods used, signaling confidence in applying these techniques to more complex scenarios or resolving even finer details of black hole environments.

In conclusion, the paper not only affirms the predictions of Einstein's theory of relativity concerning black hole shadows but also marks a significant progression in our ability to directly image and interpret astrophysical phenomena in extreme gravitational fields. As the EHT and similar observational endeavors advance, they will invariably enhance both our theoretical frameworks and observational capabilities, fostering a deeper understanding of the universe's most enigmatic objects.