On the size of the galactic centre compact radio source: diameter <20 AU
Abstract
The existence of a compact nonthermal radio source at the galactic centre was first suggested by Lynden-Bell and Rees1 as the possible signature of a black hole. Such a source was detected unambiguously by Balick and Brown2.Very long baseline interferometry (VLBI) observations of the structure of this source, hereafter referred to as Sgr A*, have been made for several years3,4. In all previous experiments, the visibility amplitudes, measured over a restricted (U, V) range, could be fitted only to the simplest model of brightness distribution, that is, to a circular gaussian. We have re-observed Sgr A* at λ3.6 cm and λ 1.35 cm with many baselines, using the more sensitive receivers and VLBI recording terminals now available. These observations set an upper limit of 20 AU (3 × l014 cm) to the diameter of Sgr A* at λ 1.35 cm and reveal for the first time an elongated structure at λ 3.6 cm, with the position angle of the long axis almost parallel to the rotation axis of the Galaxy. Sgr A* is unique in our Galaxy, but resembles most closely the compact radio sources at the centre of external galaxies. Observations of the central 4 arc s (0.2 pc) at radio and other wavelengths are best explained by a single massive collapsed object at the galactic centre.
- Publication:
-
Nature
- Pub Date:
- May 1985
- DOI:
- 10.1038/315124a0
- Bibcode:
- 1985Natur.315..124L
- Keywords:
-
- Galactic Nuclei;
- Galactic Structure;
- Milky Way Galaxy;
- Radio Sources (Astronomy);
- Very Long Base Interferometry;
- Brightness Distribution;
- Diameters;
- Normal Density Functions;
- Astrophysics