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Colloquium

Event Horizon Telescope: Earth-sized mm-VLBI array to image supermassive black holes

2019-04-05
  • Speaker : Dr. Jae-Young Kim (MPIfR) and Ilje Cho (UST, KASI)
  • Date : 2019-04-17 16:00 ~ 17:00
  • Location : JYS 331-2
  • Host : Dr. Taehyun Jung
Immediate vicinity of a supermassive black hole (SMBH) is an important place to test general relativity in strong gravity regime. Also, this is a place where mass accretion and jet formation actively occurs at the centers of active galaxies. Theoretical studies predict presence of bright ring-like emission encircling an accreting SMBH with a diameter of about 5 Schwarzschild radii, and a flux depression at the center (i.e., BH shadow). Direct imaging of the BH shadow is accordingly of great importance in modern astrophysics. However, the angular sizes of the horizon-scale structures are desperately small (e.g., ~40-50 microarcseconds (uas) diameter for the nearest best candidates). This poses serious challenges to observe them directly. Event Horizon Telescope (EHT) is a global network of sensitive radio telescopes operating at 230 GHz (1.3 mm), providing ultra-high angular resolution of 20 uas by cutting-edge very long baseline interferometry techniques. With this resolution, EHT aims to directly image the nearest SMBHs; M87 and the galactic center Sgr A* (~40-50 uas diameters). In Spring 2017, the EHT collaboration conducted a global campaign of EHT and multiwavelength observations of M87 and Sgr A*, with addition of the phased ALMA to the 1.3mm VLBI array. On April 10th, the first images of the BH shadow in M87 were published by the EHT collaboration. On behalf of the collaboration, we present main results from the EHT 2017 observations and their astrophysical implications. In addition, we will also focus on particular topics including  (i) how the EHT data processing and imaging have been validated, (ii) what are contributions to the EHT project from Korean side, and (iii) other multiwavelength observations during the EHT campaigns.