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

Abstract

Although it is widely accepted that most galaxies have supermassive black holes (SMBHs) at their centers^{1-3}, concrete proof has proved elusive. Sagittarius A* (Sgr A*)^4, an extremely compact radio source at the center of our Galaxy, is the best candidate for proof^{5-7}, because it is the closest. Previous Very Long Baseline Interferometry (VLBI) observations (at 7mm) have detected that Sgr A* is ~2 astronomical unit (AU) in size^8, but this is still larger than the "shadow" (a remarkably dim inner region encircled by a bright ring) arising from general relativistic effects near the event horizon^9. Moreover, the measured size is wavelength dependent^{10}. Here we report a radio image of Sgr A* at a wavelength of 3.5mm, demonstrating that its size is \~1 AU. When combined with the lower limit on its mass^{11}, the lower limit on the mass density is 6.5x10^{21} Msun pc^{-3}, which provides the most stringent evidence to date that Sgr A* is an SMBH. The power-law relationship between wavelength and intrinsic size (The size is 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.

18 pages, 4 figures

References in corpus (16)

• Closest Star Seen Orbiting the Supermassive Black Hole at the Centre of the Milky Way
• Viewing the Shadow of the Black Hole at the Galactic Center
• Stellar Orbits Around the Galactic Center Black Hole
• Nonthermal Electrons in Radiatively Inefficient Accretion Flow Models of Sagittarius A*
• Near-infrared flares from accreting gas around the supermassive black hole at the Galactic Centre
• The Supermassive Black Hole at the Galactic Center
• Dynamical Constraints On Alternatives To Massive Black Holes In Galactic Nuclei
• Detection of the Intrinsic Size of Sagittarius A* through Closure Amplitude Imaging (includes Online Supporting Material)
• The simultaneous spectrum of Sgr A* from 20cm to 1mm and the nature of the mm-excess
• A supermassive boson star at the galactic center?
• Hybrid Thermal-Nonthermal Synchrotron Emission from Hot Accretion Flows
• Intrinsic Size OF Sgr A*: 72 Schwarzschild Radii
• Structure of Sagittarius A* at 86 GHz using VLBI Closure Quantities
• The jet model for Sgr A*: radio and X-ray spectrum
• 7 mm lambda VLBA Observations of Sagittarius A*
• The Position, Motion, and Mass of Sgr A*

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