人馬座A
The center of the Milky Way had long puzzled astronomers, and thick dust obscures the view of it in visible light. During the mid to late 1970s, Townes together with Eric Wollman, John Lacy, Thomas Geballe and Fred Baas studied Sagittarius A, the H II region at the galactic center, at infrared wavelengths. They observed ionized neon gas swirling around the center at such velocities that the mass at the very center must be approximately equal to that of 3 million suns. Such a large mass in such a small space implied that the central object (the radio source Sagittarius A*) contains a supermassive black hole. Sagittarius A* was one of the first black holes detected; subsequently its mass has been more accurately determined to be 4.3 million solar masses.