A size of ~1AU 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 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 7mm wavelength) reported that Sgr A* is ~2astronomical 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 3.5mm, demonstrating that its size is ~1AU. When combined with the lower limit on its mass, the lower limit on the mass density is 6.5 × 1021Msolarpc-3 (where Msolar 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~wavelength1.09) explicitly rules out explanations other than those emission models with stratified structure, which predict a smaller emitting region observed at a shorter radio wavelength.
- Publication:
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Nature
- Pub Date:
- November 2005
- DOI:
- 10.1038/nature04205
- arXiv:
- arXiv:astro-ph/0512515
- Bibcode:
- 2005Natur.438...62S
- Keywords:
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- Astrophysics
- E-Print:
- 18 pages, 4 figures