The distance between our Solar System and Sagittarius A*, the 4-million-solar-mass black hole at the center of our Milky Way Galaxy, is approximately 25,800 light-years, about 1,900 light-years closer than previous estimate, according to an analysis of data from the Japanese VLBI (Very Long Baseline Interferometer) project VERA (VLBI Exploration of Radio Astrometry).
Position and velocity map of the Milky Way Galaxy; arrows show position and velocity data for 224 objects used to model the Galaxy; the solid black lines show the positions of the Galaxy’s spiral arms; the colors indicate groups of objects belonging the same arm. Image credit: NAOJ.
“Because Earth is located inside the Milky Way, we can’t step back and see what our Galaxy looks like from the outside,” said Dr. Tomoya Hirota, an astronomer from the Mizusawa VLBI Observatory at the National Astronomical Observatory of Japan and the Department of Astronomical Sciences at SOKENDAI, and his colleagues from the VERA Collaboration.
“Astrometry, accurate measurement of the positions and motions of objects, is a vital tool to understand the overall structure of the Galaxy and our place in it.”
“VERA was initiated by National Astronomical Observatory of Japan in the 2000s,” they added.
“The project was designed to dedicate for the VLBI astrometry observations to reveal 3D velocity and spatial structures in the Milky Way.”
“It involved four 20-m radio telescopes in Japan: at Mizusawa, Iriki, Ogasawara, and Ishigaki-jima stations.”
Using data from the first VERA astrometry catalog, the astronomers modeled the structure of the Milky Way to estimate the fundamental parameters such as the distance toward the Galactic center and the velocity of the Sun around it.
“Our results suggest that the center of the Galaxy, and the supermassive black hole which resides there, is located 25,800 light-years from Earth,” they said.
“This is closer than the official value of 27,700 light-years adopted by the International Astronomical Union in 1985.”
“The velocity component of the map indicates that the Sun is traveling at 227 km/s as it orbits around the Galactic center. This is faster than the official value of 220 km/s.”
The VERA researchers now plan to observe more objects, particularly ones close to Sagittarius A*, to better characterizes the structure and motion of the Milky Way.
“As part of these efforts VERA will participate in EAVN (East Asian VLBI Network) comprised of radio telescope located in Japan, South Korea, and China,” they said.
“By increasing the number of telescopes and the maximum separation between telescopes, EAVN can achieve even higher accuracy.”
The VERA catalog was published recently in the Publications of the Astronomical Society of Japan.
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Tomoya Hirota et al. (VERA Collaboration). 2020. The First VERA Astrometry Catalog. Publications of the Astronomical Society of Japan 72 (4): 50; doi: 10.1093/pasj/psaa018
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