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[천문학콜로키움]2019.11.26 (화) 손봉원 박사, 조일제 연구원

행사 및 세미나 게시물 : 상세, 작성자, 작성일, 조회수, 첨부파일 정보를 제공
작성자 학과세미나 작성일 2019/11/19 조회수 317
날짜 2019-11-26 시간 16:30 ~ 18:00 장소 제 2 과학관 425호
첨부파일 첨부파일없음

1)

제목 First M87 Event Horizon Telescope Results - The Shadow of the Supermassive Black Hole

일시 : 2019년 11월 26일 화요일 오후 4시 30분 ~ 6시
장소 : 경북대학교 제2과학관 425호
연사 : 손봉원 박사님, 한국천문연구원

요약문 I will briefly report the motivation and the recent results of Event Horizon Telescope Project.

When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope (EHT), a global very long baseline interferometry (VLBI) array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42 +/-3 micro-arcsec, which is circular and encompasses a central depression in brightness with a flux ratio > 10 : 1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M = (6.5+/-0.7) x 10^9 M_{Sun}. Our radio-wave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.


2)

제목 : The black hole shadow imaging with the Event Horizon Telescope

일시 : 2019년 11월 26일 화요일 오후 4시 30분 ~ 6시

장소 : 경북대학교 제2과학관 425호

연사 : 조일제 연구원 (UST, 한국천문연구원)

요약문 : Event Horizon Telescope (EHT) is a global very long baseline interferometry (VLBI) network of sensitive radio telescopes operating at 230 GHz (1.3 mm). This provides ultra-high angular resolution of 20 micro-arcseconds, aiming to directly image the nearest super massive black holes (SMBHs); M87 and the galactic center Sgr A* (~40-50 micro-arcseconds diameters). In April 10th, the first imaging results of black hole shadow of M87 were released. This has a great importance as the first observational probe of the black hole shadow which has been theoretically predicted as a ring-like emission affected by the general relativistic effect under a strong gravitational field of SMBH. To robustly ensure the results, the EHT Collaboration has been developing newer interferometric imaging techniques (e.g., eht-imaging-library, SMILI, dynamical imaging), as well as using an established method (CLEAN). With these, the EHT Collaboration has designed various strategies for convincing imaging results. In this talk, I review the VLBI imaging techniques and how the robustness of black hole shadow images have been validated so that the results can be ensured against well known uncertainties or biases in the interferometric imaging.

행사 및 세미나 게시물 : 다음글 제목, 현재글 제목, 이전글 제목 정보를 제공, 제목을 누르면 게시물의 상세페이지로 이동
다음글 : 다음 게시물이 없습니다
현재글 : [천문학콜로키움]2019.11.26 (화) 손봉원 박사, 조.. 학과세미나 2019/11/19
이전글 : [천문학콜로키움]2019.11.12 (화) 정애리 교수.. 학과세미나 2019/11/06