Sagittarius A
Sgr A West looks like a three-arm spiral from the point of view of the Earth. Actually it is made of several dust and gas clouds, which orbit and fall onto Sagittarius A* at velocities as high as 1,000 kilometers per second. The surface layer of these clouds is ionized. The source of ionisation is the population of massive stars that also occupy the central parsec of the galaxy. Over hundred such OB stars have been identified so far.