First M87 Event Horizon Telescope Results. VII. Polarization of the Ring (2105.01169v1)

Abstract: In 2017 April, the Event Horizon Telescope (EHT) observed the near-horizon region around the supermassive black hole at the core of the M87 galaxy. These 1.3 mm wavelength observations revealed a compact asymmetric ring-like source morphology. This structure originates from synchrotron emission produced by relativistic plasma located in the immediate vicinity of the black hole. Here we present the corresponding linear-polarimetric EHT images of the center of M87. We find that only a part of the ring is significantly polarized. The resolved fractional linear polarization has a maximum located in the southwest part of the ring, where it rises to the level of about 15%. The polarization position angles are arranged in a nearly azimuthal pattern. We perform quantitative measurements of relevant polarimetric properties of the compact emission and find evidence for the temporal evolution of the polarized source structure over one week of EHT observations. The details of the polarimetric data reduction and calibration methodology are provided. We carry out the data analysis using multiple independent imaging and modeling techniques, each of which is validated against a suite of synthetic data sets. The gross polarimetric structure and its apparent evolution with time are insensitive to the method used to reconstruct the image. These polarimetric images carry information about the structure of the magnetic fields responsible for the synchrotron emission. Their physical interpretation is discussed in an accompanying publication.

• The paper reports polarimetric imaging of M87's ring, revealing up to 15% linear polarization in the southwest segment.
• The study applies rigorous imaging and cross-validation techniques to ensure robust calibration of the polarimetric data.
• The findings suggest highly organized magnetic fields near the event horizon, informing models of accretion and jet launching.

Overview of the Event Horizon Telescope's Polarimetric Imaging of M87

In this paper, the Event Horizon Telescope (EHT) collaboration reports their comprehensive polarimetric analysis of the supermassive black hole at the center of the M87 galaxy. The observations at a wavelength of 1.3 mm, conducted in April 2017, revealed a distinctive ring-like morphology around the black hole, attributed to synchrotron emission. This research extends previous analysis by introducing polarimetric imaging, which offers new insights into the magnetic field structure near the event horizon.

Key Findings and Methodology

The EHT presents linear polarization measurements indicating that only parts of the detected emission ring are significantly polarized, with the highest polarization fraction reaching approximately 15% in the southwest segment of the ring. The electric vector position angle (EVPA) of the polarized emission displays a nearly azimuthal arrangement. These findings suggest highly organized magnetic fields in the vicinity of the black hole, shedding light on models of accretion and relativistic jet-launching mechanisms.

The polarimetric data underwent extensive reduction and calibration through multiple independent imaging and modeling techniques, each cross-validated against synthetic data sets. Despite methodological differences, the global polarimetric structure remained consistent, underscoring the robustness of the order and configuration of the magnetic fields inferred from these observations.

Implications and Future Prospects

The polarimetric imaging by EHT not only provides empirical data to constrain theoretical models of magnetic field interactions around supermassive black holes but also challenges existing models of relativistic dynamics in these extreme environments. This paper sets the groundwork for further investigations into the jet-launching processes and presents an opportunity to refine magnetohydrodynamic simulations of such astrophysical systems.

Future research leveraging the EHT network's capabilities, particularly with the enhanced array configurations and concurrent high-frequency observations, could yield more intricate details regarding the magnetic field dynamics and jet physics. Additionally, the potential for resolving intrinsic variability and Faraday rotation effects in the source could lead to a more profound understanding of the fundamental processes at play in active galactic nuclei.

This paper represents a rigorous step in the continuum of observational astrophysics research aimed at disentangling the complexities of magnetic fields in relativity-dominated regimes. As the EHT collaboration continues to refine both their techniques and theoretical models, further revelations about the inner workings of black holes are anticipated, thereby enhancing our understanding of these enigmatic cosmic phenomena.