Faster Earth, closer to the black hole in the new galaxy map

Earth has just become 7 km / s faster and about 2,000 light years closer to the supermassive black hole at the center of the Milky Way. But don’t worry, this doesn’t mean our planet is plunging towards the black hole. Instead the changes are the result of a better model of the Milky Way based on new observation data, including a catalog of objects observed over 15 years by the Japanese radio astronomy project VERA.

VERA (VLBI Exploration of Radio Astrometry, from the way “VLBI” stands for Very Long Baseline Interferometry) began in 2000 to map three-dimensional velocity and space structures in the Milky Way. VERA uses a technique known as interferometry to combine data from radio telescopes scattered across the Japanese archipelago to achieve the same resolution as a 2300 km diameter telescope. The measurement accuracy obtained with this resolution, 10 micro-seconds of arc, is in theory sharp enough to resolve a US penny placed on the surface of the Moon.

Since the Earth is inside the Milky Way, we cannot step back and see what the Galaxy looks like from the outside. Astrometry, accurate measurement of the positions and movements of objects, is a fundamental tool for understanding the overall structure of the Galaxy and our place in it. This year, the first VERA astrometric catalog was released containing data for 99 objects.

Based on the VERA Astrometry Catalog and recent observations by other groups, the astronomers constructed a map of position and velocity. From this map they calculated the center of the Galaxy, the point around which everything revolves. The map suggests that the center of the Galaxy and the supermassive black hole that resides there are 25,800 light-years from Earth. This is closer than the official value of 27700 light years adopted by the International Astronomical Union in 1985. The velocity component of the map indicates that the Earth is traveling at 227 km / s as it orbits the Galactic Center. This is faster than the official value of 220 km / s.

Now VERA hopes to observe more objects, particularly those near the central supermassive black hole, to better characterize the structure and motion of the Galaxy. As part of these efforts, VERA will participate in the East Asian VLBI Network (EAVN) consisting of radio telescopes located in Japan, South Korea and China. By increasing the number of telescopes and the maximum distance between telescopes, EAVN can achieve even greater accuracy.

“The First VERA Astrometry Catalog” by VERA Collaboration et al. appeared in the publications of the Astronomical Society of Japan in August 2020.

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