First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring (1906.11242v1)

Abstract: The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider the physical implications of the asymmetric ring seen in the 2017 EHT data. To this end, we construct a large library of models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by general relativistic ray tracing. We compare the observed visibilities with this library and confirm that the asymmetric ring is consistent with earlier predictions of strong gravitational lensing of synchrotron emission from a hot plasma orbiting near the black hole event horizon. The ring radius and ring asymmetry depend on black hole mass and spin, respectively, and both are therefore expected to be stable when observed in future EHT campaigns. Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity. If the black hole spin and M87's large scale jet are aligned, then the black hole spin vector is pointed away from Earth. Models in our library of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets. At the same time, in those models that produce a sufficiently powerful jet, the latter is powered by extraction of black hole spin energy through mechanisms akin to the Blandford-Znajek process. We briefly consider alternatives to a black hole for the central compact object. Analysis of existing EHT polarization data and data taken simultaneously at other wavelengths will soon enable new tests of the GRMHD models, as will future EHT campaigns at 230 and 345 GHz.

• The paper demonstrates that the asymmetry in M87’s ring is primarily due to strong gravitational lensing from a spinning Kerr black hole.
• It employs GRMHD simulations with synthetic imaging to effectively rule out non-spinning models that fail to power energetic jets.
• The analysis integrates spectrum, radiative efficiency, and X-ray constraints, paving the way for more precise future EHT observations.

Analysis of the Physical Origins of M87's Asymmetric Ring Observed by the EHT

The paper conducted by the Event Horizon Telescope (EHT) Collaboration marks a pivotal evaluation of the asymmetric ring structure observed at the core of the galaxy M87. Through extensive analysis based on data obtained in 2017, this paper presents a comprehensive exploration of the possible physical explanations for this asymmetry, utilizing insights garnered from GRMHD simulations and synthetic imaging via relativistic ray tracing.

Observations and Theoretical Framework

The consistency between the EHT's observations of the ring's asymmetry and the theoretical predictions of strong gravitational lensing effects on synchrotron radiation near a black hole makes a compelling case. The analysis underscores that the ring's radius and asymmetry are directly influenced by critical properties of the black hole itself, notably its mass and spin. These characteristics, integral to the Kerr metric model as predicted by general relativity, suggest the presence of a spinning Kerr black hole at M87's center.

Models that incorporate non-spinning black holes were found inadequate, primarily due to their inability to generate sufficiently energetic jets, highlighting the indispensable role of black hole spin. The EHT's data favored models where the jet is driven by energy extracted from the black hole's spin, akin to mechanisms such as the Blandford-Znajek process. This analysis also cast proposals for non-black hole central entities in a skeptical light, emphasizing the robustness of the black hole hypothesis.

Technical Analysis and Model Constraints

A key aspect of the research involved correlating the observational data with a simulated library of GRMHD models. The inherent turbulence and dynamic nature of these models introduced significant challenges in achieving tight constraints; however, the methodology allowed the rejection of several models inconsistent with observational data. Notably, the analysis showed that models with aligned jet axes and black hole spins pointing away from Earth succeeded in representing the observed asymmetry.

The detailed calculations also involved constraining the physical parameters by leveraging complementary data, including spectrum analysis, radiative efficiency assessments, and X-ray luminosity limitations. This multi-faceted approach led to the exclusion of scenarios where the black hole was non-spinning or exhibits inadequate jet power.

Implications and Future Prospects

While this research substantiates the predominant theories regarding black hole environments, it also highlights areas where improvements in model precision are necessary. Particularly, the nature of the electron distribution within the accretion flow remains an area rich for further research.

Looking forward, future observations by the EHT at higher frequencies and other electromagnetic spectrum data, including polarization studies, promise to refine these insights further. Enhanced resolution could discern finer features of the ring and more accurately measure its breadth, possibly leading to stronger constraints on theoretical models. Additionally, repeat observational campaigns over time could explore potential variability and its implications on several astrophysical processes.

As the understanding of M87's core phenomenon evolves, this paper serves not only as a rigorous affirmation of certain theoretical frameworks but also as a foundational work empowering future explorations into the extreme physics governing black hole dynamics. Through synergy between observational prowess and theoretical insight, the quest for unraveling the complete picture of such enigmatic regions in the universe continues to progress.