Glossary term: Sagittarius A*

Description: Observations of the motions of stars and gas around the center of the Milky Way provide indirect evidence of a supermassive black hole with a mass around 4.5 million times that of the Sun, and approximately 40 million kilometers across, located about 27,000 light years away from Earth. Sagittarius A* (Sagittarius A-star) is the compact radio source that is associated with the supermassive black hole. It has been observed in a range of wavelengths, most notably in radio. The name Sagittarius is because it is located in the constellation of Sagittarius as observed from Earth; the letter A is because it is the brightest and first extrasolar radio source discovered in the constellation; the asterisk is because in physics atoms in excited states are denoted by *, and Sagittarius A* was an exciting discovery.

In 2022, the Event Horizon Telescope Collaboration released the first ever image of the silhouette ("shadow") of the black hole associated with Sagittarius A*.

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