Ara is embedded in the southern Milky Way, where dense interstellar dust clouds hide the distant star clouds. The bright open cluster NGC 6193, embedded in the large emission nebula NGC 6188, is visible on dark, clear nights.
NGC 6188 is an interstellar carnival of young blue stars, hot red gas, and cool dark dust. Dark shapes with bright edges winging their way through dusty NGC 6188 are tens of light-years long. Located 4300 light years away, NGC 6188 is home to the Ara OB1 association, a group of bright young stars that spans a full square degree of the southern sky. Its nucleus forms the open cluster NGC 6193, embedded in an area cloaked by thick gas clouds and obscuring lanes of dust. Its stars are so bright that some of their light reflects off the interstellar dust, forming a diffuse blue glow.
The massive young stars of the Ara OB1 association sculpt the fantastic shapes and illuminate the nebular with stellar winds and intense ultraviolet radiation. The hottest stars of the cluster are two closely spaced O-type giants HD 150135 and HD 150136. HD 150136 is a remarkable binary system comprised of a massive O3 and O6 V type stars which are nearly in contact with each other. Colliding stellar winds from the pair may be responsible for the prodigious X-ray emission emitted from this bright stellar system.
NGC 6193, and the surrounding emission nebula NGC 6188 lie along the edge of an immense molecular cloud and an expanding bubble of hydrogen gas, spanning some 300 light years across. Ultraviolet radiation from the O-type giant stars of NGC 6193 is presently eroding the eastern edge of the molecular cloud, and may be triggering further star formation in other regions inside it.
NGC 6193 formed about three million years ago from the surrounding gas, and appears unusually rich in close binary stars. A likely evolutionary scenario of this region begins with the formation of the older cluster NGC 6167, which is currently at the center of the expanding gas bubble. Powerful winds blasted from the first supernovae in this cluster produced the expanding bubble of neutral hydrogen gas. The expanding shell subsequently plowed into the surrounding interstellar medium, triggering the formation of the Ara OB1 association, and of NGC 6193 along the edge of the bubble, some 1 to 3 million years ago.