![]() In 2019, measurements made with the High-resolution Airborne Wideband Camera-Plus (HAWC+) mounted in the SOFIA aircraft revealed that magnetic fields cause the surrounding ring of gas and dust, temperatures of which range from −280 to 17,500 ☏ (99.8 to 9,977.6 K −173.3 to 9,704.4 ☌), to flow into an orbit around Sagittarius A*, keeping black hole emissions low. The telescope's measurement of these black holes tested Einstein's theory of relativity more rigorously than has previously been done, and the results match perfectly. The proper motion of Sgr A* is approximately −2.70 mas per year for the right ascension and −5.6 mas per year for the declination. For comparison, Earth is 150 million kilometres (1.0 astronomical unit 93 million miles) from the Sun, and Mercury is 46 million km (0.31 AU 29 million mi) from the Sun at perihelion. At a distance of 26,000 light-years (8,000 parsecs), this yields a diameter of 51.8 million kilometres (32.2 million miles). Their result gives an overall angular size for the source of 51.8 ☒.3 μas. The radio emission from Sgr A* varies on the order of minutes, complicating the analysis. Radio images are produced from data by aperture synthesis, usually from night long observations of stable sources. The data were collected by eight radio observatories at six geographical sites. This image took five years of calculations to process. This is the second image of a black hole. The image, which is based on radio interferometer data taken in 2017, confirms that the object contains a black hole. ![]() On May 12, 2022, the first image of Sagittarius A* was released by the Event Horizon Telescope Collaboration. Observation and description The diameter of Sagittarius A* is smaller than the orbit of Mercury. The observed radio and infrared energy emanates from gas and dust heated to millions of degrees while falling into the black hole. The black hole itself is not seen, only nearby objects whose behavior is influenced by the black hole. This is the second confirmed image of a black hole, after Messier 87's supermassive black hole in 2019. In May 2022, astronomers released the first image of the accretion disk around the horizon of Sagittarius A*, confirming it to be a black hole, using the Event Horizon Telescope, a world-wide network of radio observatories. Reinhard Genzel and Andrea Ghez were awarded the 2020 Nobel Prize in Physics for their discovery that Sagittarius A* is a supermassive compact object, for which a black hole was the only plausible explanation at the time. The current value of its mass is 4.154 ☐.014 million solar masses. Based on mass and increasingly precise radius limits, astronomers 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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