Nakamura, Masanori

Greenland Telescope (GLT) Project --- A Direct Confirmation of Black Hole with Sub-millimeter VLBI

Author list: J. C. Algaba, K. Asada, B. Chen, M.-T. Chen, J. Han, P. H. P. Ho, S.-N. Hsieh, T. Huang, M. Inoue, P. Koch, C.-Y. Kuo, P. Martin-Cocher, S. Matsushita, Z. Meyer-Zhao, H. Nishioka, G. Nystrom, N. Pradel, P. Raffin, H.-Y. Shen (ASIAA), and the Greenland Telescope Project Team (CfA, MIT Haystack Observatory, and NRAO)

Direct observation of black holes has not yet been achieved. If we are able to do so, we will access for the first time matter and electromagnetic fields under the extremely strong gravity, which could test Einstein’s theory of general relativity. The GLT project is deploying a new sub-millimeter (sub-mm) VLBI station in Greenland. Our primary scientific goal is to image a shadow of the supermassive black hole (SMBH) of six billion solar mases in M87 at the center of the Virgo cluster of galaxies. The expected SMBH shadow size of 40-50 μas requires superbly high angular resolution, suggesting that the sub-mm VLBI would be the only way to obtain the shadow image. The Summit station in Greenland enables us to establish baselines longer than 8,000 km with ALMA in Chile and SMA in Hawaii as well as providing a unique u-v coverage for imaging M87. Our VLBI network will achieve a superior angular resolution of about 20 μas at 350 GHz, corresponding to ~ 2.5 R_s of the SMBH in M87. We have been monitoring the atmospheric opacity at 230 GHz since Aug. 2011; we have confirmed the value on site during the winter season is comparable to the ALMA site thanks to high altitude of 3,200 m and low temperature of -50°. We will report current status and future plan of the GLT project towards our expected first light on 2015 - 2016.