The star S0-2 orbits very close to the black hole at the centre of the Milky Way. More than a decade's worth of data from the Keck telescope in Hawaii has allowed Andrea Ghez of the University of California, Los Angeles, and her colleagues to produce a model of this star's orbit around the black hole that is by far the most accurate to date.
Using measurements of S0-2's movement back and forth along a straight line between it and Earth, and also of its movements from side to side, the researchers estimate that the black hole, if stationary, has a mass of between 4 million and 5 million times that of the Sun, and is 8–8.9 kiloparsecs from Earth.
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Astronomy: That's the weigh to do it. Nature 456, 678 (2008). https://doi.org/10.1038/456678b
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DOI: https://doi.org/10.1038/456678b
