First Results of the Event Horizon Telescope

Abstract

On April 10, 2019, the Event Horizon Telescope (EHT) collaboration has revealed the first-ever images of a black hole shadow. This exciting news immediately ran around the world. The EHT links ground-based radio telescopes around the globe to form an Earth-sized computational telescope with an unprecedented high angular resolution using very long baseline interferometry (VLBI) at millimeter wavelengths. The first images they successfully obtained are the visual evidence of a supermassive black hole (SMBH) at the center of a giant elliptical galaxy M87. The final images reveal an asymmetric ring morphology of the central compact radio source with a diameter of 42±3 μas. This strongly suggests that we see gravitationally lensed emission from plasma located very close to the SMBH event horizon. From the measured ring size, we derived a SMBH mass of (6.5±0.7)×10⁹M⦿. The image provides solid evidence for the presence of a BH at the center of M87 and supports the longstanding hypothesis that a SMBH powers an active galactic nucleus. Moreover, it demonstrates that VLBI at millimeter/submillimeter wavelengths offers a powerful method to explore gravity in its most extreme limit and at a previously inaccessible mass scale. An existence of the black hole in the universe, Albert Einstein first predicted it over a century ago with his general theory of relativity, has been finally confirmed by the EHT collaboration. In this volume, we will overview the project, and introduce data processing and imaging. Then, we describe the comparison with the theory and the interpretation of observations to conclude the physics behind. Future direction of the EHT is also briefly outlined.