1998/09/17 by K. Y. Lo, Zhi-Qiang Shen, Z. -Q. Shen +4 · 2 citations
Engineering · Physics and Astronomy · #Accretion (finance) #Active galactic nucleus #Advection #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Black hole (networking) #Galactic Center #Galaxy #Heat Transfer Mechanisms #Milky Way #Observable #Optics #Physics #Quantum mechanics #RADIUS #Sagittarius #Sagittarius A* #Scattering #Schwarzschild radius #Supermassive black hole #Very Long Baseline Array #astro-ph
paper · pdf · doi:10.1086/311726
15 pages including 2 ps figures and 1 table, to appear in ApJ Letters
arxiv created 1998/09/17 · openalex publication_date 1998/11/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Recent proper motion studies of stars at the very center of the Galaxy strongly suggest that Sagittarius A*, the compact nonthermal radio source at the Galactic center, is a 2.5 × 10 6 M ☉ black hole. By means of near-simultaneous multiwavelength Very Long Baseline Array measurements, we determine for the first time the intrinsic size and shape of Sgr A* to be 72 R sc (⋆) by less than 20 R sc (⋆), with the major axis oriented essentially north-south, where R sc (⋆) (≡ 7.5 × 10 11 cm) is the Schwarzschild radius for a 2.5 × 10 6 M ☉ black hole. Contrary to previous expectation that the intrinsic structure of Sgr A* is observable only at λ≤1 mm, we can discern the intrinsic source size at λ=7 mm because (1) the scattering size along the minor axis is half that along the major axis and (2) the near-simultaneous multiwavelength mapping of Sgr A* with the same interferometer makes it possible to extrapolate precisely the minor axis scattering angle at λ=7 mm. The intrinsic size and shape place direct constraints on the various emission models for Sgr A*. In particular, the advection-dominated accretion flow model may have to incorporate a radio jet in order to account for the structure of Sgr A*.