Milky Way X-ray activity. X-ray image of the central portion of the Milky Way galaxy, showing X-ray activity. This inner region of the Milky Way lies 26,000 light years from Earth. At its centre lies Sagittarius A-star (Sgr A*), a behemoth black hole containing 4 million times the Sun's mass. Sgr A* regularly produces bright X-ray flares today, but astronomers know it was much more active in the past. Imaged by the X-Ray Telescope (XRT) onboard NASA's Swift spacecraft.