宇宙科学談話会

ISAS Space Science Colloquium & Space Science Seminar

FY2022

ENGLISH

Imaging of the Supermassive Black Hole in Our Galaxy, Sgr A* with the Event Horizon Telescope

KOFUJI Yutaro(小藤 由太郎)
Department of Astronomy, School of Science, the University of Tokyo/National Astronomical Observatory of Japan(NAOJ)

The first event horizon scale image of the supermassive black hole in our Galaxy, Sgr A* was captured by the Event Horizon Telescope(EHT) Collaboration. EHT is the Very Long Baseline Interferometry (VLBI) that links radio dishes around the world to create an Earth-sized telescope virtually. High-resolution observations of EHT enable us to see the vicinity of the black hole. The obtained image of the black hole shadow is consistent with the prediction of general relativity.
The observations were done in 2017 April at a wavelength of 1.3mm. In the imaging process, we used 4 imaging methods, CLEAN, regularized maximum likelihood (RML) methods, and a Bayesian posterior sampling method. The main challenges of Sgr A* imaging are the rapid time variation and interstellar scattering, and the mitigation processes for these effects are developed. Each imaging method has imaging parameters including these mitigation processes and we performed the parameter survey using ~200 thousand parameter combinations. From these parameters, we choose ~10 thousand "Top Set" parameters that can distinguish different morphologies. The Sgr A* images reconstructed with "Top Set" parameters are clustered into 4 morphologies, 3 ring clusters that have different brightness distributions and a small number of non-ring images. Based on the multiple tests, we conclude that Sgr A* is highly likely to have ~50 micro-arcsecond ring structure. The comparison between the reconstructed images and the theoretical simulations shows that reconstructed images are consistent with the shadow of the Kerr black hole which weighs ~4 million solar masses.

A 2F Conf. room(1236) / 研究管理棟2階会議場(1236号室)、Via Zoom / Zoom 開催

ENGLISH

TMT science cases and the project status

AOKI Wako(青木 和光)
National Astronomical Observatory of Japan(NAOJ)

The Thirty Meter Telescope (TMT) project is an international collaboration of five countries to construct an optical/infrared extremely large telescope. It will achieve more than three times higher resolving power and 100 times higher sensitivity for point sources than the current large telescopes. This will significantly enhance studies of extrasolar planets to enable direct imaging of earth-like planets and determining compositions of their atmospheres that might include signatures of life. TMT will also explore the light from first stars in distant galaxies and determine elements produced by explosions studied by multi-messenger astronomy. The project expects collaborations with space sciences and Solar System missions in 2030s and beyond. The TMT project has been engaging community in Hawaii to have understanding for astronomy and the telescope, having remarkable progress in dialogues in the community. Founding a new management organization involving native Hawaiians was recently approved by Hawaii state legislature. Following the recommendations in the Decadal Survey, NSF will start reviewing process for the US-ELT project including TMT. The status and prospect of the project are presented in this seminar.

A 2F Conf. room(1236) / 研究管理棟2階会議場(1236号室)、Via Zoom / Zoom 開催

ENGLISH

Eruptions from Young Solar-like Stars and Impact of Habitable Environments of Rocky Exoplanets

Vladimir Airapetian
NASA Goddard Space Flight Center and American University

Is life unique to Earth or a common phenomenon in the Solar System and the Universe? This fundamental question is one of the greatest puzzles of modern science. Earth's evident long-term habitability makes it a key data point for understanding the formation of habitable worlds in the Universe. To address this fundamental question, we need to know how the basic requirements for life as we know it such as liquid water, organic compounds and persistent external energy fluxes promoted the emergence and complexification of biological systems on early Earth and how they were impacted by planetary and solar properties. The early Solar System was a chaotic place, likely subject to frequent large impacts as well as the violently changing space weather (energetic ionizing radiation flux from the solar corona, wind and transient events) from the infant (< 100 Myr) and toddler (400-600 Myr) Sun. Understanding the conditions that allowed for the emergence of life on early Earth, and whether other inner planets in our Solar System possibly also supported habitable conditions early in their histories is a promising way to address these questions. Thus, the knowledge of the heliospheric environments surrounding the early Venus, Earth and Mars is critical for evaluation of the basic requirements for life as we know it including liquid water and organic compounds. Here, I will describe recent observations of young solar-like stars and the Sun as inputs for our 3D MHD models of the corona, the wind and transient events (flares, coronal mass ejections and solar energetic particle events) and discuss their impact on atmospheric erosion and chemistry of early Earth. I will use these constrained energy fluxes to describe our recent atmospheric chemistry models impacted by energetic particles from the young solar-like stars and formation and precipitation of biologically relevant molecules on rocky exoplanets. I will then highlight our results of laboratory experiments of proton irradiation of mildly reduced gas mixtures and their implications to the climate, prebiotic chemistry and the rise of habitability in exoplanetary systems.

A 2F Conf. room(1236) / 研究管理棟2階会議場(1236号室)、Via Zoom / Zoom 開催