The black hole in the binary star GS 2000+25 has a mass of about 8 M?. What is its radius in kilometers? The black hole at the center of the Milky Way has a mass of 4.2 × 106 M?. What is its radius in solar radii? The black hole at the center of the giant elliptical galaxy M87 has a mass of 2.7 × 109 M?. What is its radius in Astronomical Units? For comparison, what is the radius of Neptune's orbit?