Astrophysics behind the First Images of a Black Hole

Hung-Yi Pu^1,2*

¹Department of Physics, National Taiwan Normal University, Taipei, Taiwan
²Academia Sinica Institute of Astronomy and Astrophysics, Taipei, Taiwan

* Presenter:Hung-Yi Pu, email:hypu@ntnu.edu.tw

Black holes, bizarre spacetime structures, are astrophysical objects which exhibit several unique features in the Universe. Predicted by Einstein's general theory of relativity, a black hole can cast shadows by capturing photons emitted by the surrounding hot but dilute gas, resulting in a lensed image of photon orbits. The Event Horizon Telescope (EHT), a Earth-size virtual telescope, is a global very-long-baseline interferometry (VLBI) network for synchronizing radio observations from telescope facilities all over the world. With unprecedented angular resolution and sensitivity at 1.3 mm (230 GHz), in 2017, EHT performed observations for the compact and jetted radio source at the core of the elliptical galaxy M87 for four different days, which made it possible to resolve and reconstruct event horizon scale images of the supermassive black hole candidate. After years of data analysis of the 2017 observation, on April 10th 2019, EHT collaboration reported the first images of a black hole: the observed ring-like structure is consistent with the shadow features expected from a spinning Kerr black hole with 6.5 billion solar mass, and the asymmetric ring implies that the black hole spin vector is pointed away from Earth, provided that the black hole spin and M87's large scale jet are aligned. The talk will cover how these interpretations are obtained, and introduce related astrophysics, including black hole accretion, jet and shadow.

Keywords: black hole , M87, Event Horizon Telescope, accretion, jet