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A size of ~1 AU for the radio source Sgr A* at the centre of the Milky Way

Shen, Zhi-Qiang and Lo, K. Y. and Liang, M. C. and Ho, Paul T. P. and Zhao, J.-H. (2005) A size of ~1 AU for the radio source Sgr A* at the centre of the Milky Way. Nature, 438 (7064). pp. 62-64. ISSN 0028-0836.

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Although it is widely accepted that most galaxies have supermassive black holes at their centres, concrete proof has proved elusive. Sagittarius A* (Sgr A*), an extremely compact radio source at the centre of our Galaxy, is the best candidate for proof, because it is the closest. Previous very-long-baseline interferometry observations (at 7 mm wavelength) reported that Sgr A* is ~2 astronomical units (au) in size, but this is still larger than the 'shadow' (a remarkably dim inner region encircled by a bright ring) that should arise from general relativistic effects near the event horizon of the black hole. Moreover, the measured size is wavelength dependent. Here we report a radio image of Sgr A* at a wavelength of 3.5 mm, demonstrating that its size is ~1 au. When combined with the lower limit on its mass11, the lower limit on the mass density is 6.5 × 10^21 M_⊙ pc^-3 (where M_⊙ is the solar mass), which provides strong evidence that Sgr A* is a supermassive black hole. The power-law relationship between wavelength and intrinsic size (size proportional to wavelength^1.09) explicitly rules out explanations other than those emission models with stratified structure, which predict a smaller emitting region observed at a shorter radio wavelength.

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Liang, M. C.0000-0002-5294-9344
Additional Information:© 2005 Nature Publishing Group. Received 1 July; accepted 31 August 2005. The Very Large Array and the Very Long Baseline Array are operated by the National Radio Astronomy Observatory, which is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities Inc. Z.-Q.S. acknowledges support from the One-Hundred-Talent programme of the Chinese Academy of Sciences.
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Chinese Academy of Sciences One-Hundred-Talent programmeUNSPECIFIED
Issue or Number:7064
Record Number:CaltechAUTHORS:20150330-090926147
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Official Citation:Shen, Z.-Q., Lo, K. Y., Liang, M. C., Ho, P. T. P., & Zhao, J. H. (2005). A size of [sim]1[thinsp]au for the radio source Sgr A[ast] at the centre of the Milky Way. [10.1038/nature04205]. Nature, 438(7064), 62-64.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56202
Deposited By: Jason Perez
Deposited On:30 Mar 2015 23:58
Last Modified:09 Mar 2020 13:19

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