Based on mass and increasingly precise radius limits, astronomers have concluded that Sagittarius A* must be the Milky Way's central supermassive black hole. The observations of several stars orbiting Sagittarius A*, particularly star S2, have been used to determine the mass and upper limits on the radius of the object. Brown, who understood that the strongest radio emission from the center of the galaxy appeared to be due to a compact nonthermal radio object. The asterisk was assigned in 1982 by Robert L. The asterisk * is a later addition and was added because its discovery was considered "exciting", in parallel with the nomenclature for excited state atoms which are denoted with an asterisk (for example, the excited state of helium would be He*). They arranged these sources by constellation and then assigned capital letters in order of brightness within each constellation, with A denoting the brightest radio source within the constellation. Kraus, Hsien-Ching Ko, and Sean Matt listed the radio sources they identified with the Ohio State University radio telescope at 250 MHz.
The name Sagittarius A* follows from historical reasons.
The object is a bright and very compact astronomical radio source. It is located near the border of the constellations Sagittarius and Scorpius, about 5.6° south of the ecliptic, visually close to the Butterfly Cluster (M6) and Lambda Scorpii. Sagittarius A* ( / ˈ eɪ s t ɑːr/ AY star), abbreviated Sgr A* ( / ˈ s æ dʒ ˈ eɪ s t ɑːr/ SAJ AY star ), is the supermassive black hole at the Galactic Center of the Milky Way. Sagittarius A* imaged by the Event Horizon Telescope in 2017, released in 2022
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