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In 1999 a violent outburst at V4641 Sgr was thought to have revealed the location of the closest known black hole to Earth, but later investigation increased its estimated distance by a factor of 15. The complex radio source Sagittarius A is also in Sagittarius, near its western boundary with Ophiuchus. Astronomers believe that one of its components, known as Sagittarius A*, is associated with a supermassive black hole at the center of the galaxy, with a mass of 2.6 million solar masses. Although not visible to the eye, Sagittarius A* is located off the top of the spout of the Teapot asterism. The Sagittarius Dwarf Elliptical Galaxy is located just outside the Milky Way.