Free Astronomy Magazine May-June 2015

MAY-JUNE 2015 SPACE CHRONICLES A grand extra vaganza of new stars by ESO T his dramatic landscape in the southern constellation of Ara (The Altar) is a treasure trove of celestial objects. Star clusters, emission nebulae and active star- forming regions are just some of the riches observed in this region lying some 4000 light-years from Earth. This beautiful new image is the most detailed view of this part of the sky so far, and was taken using the VLT Survey Telescope at ESO’s Paranal Observatory in Chile. At the centre of the image is the open star cluster NGC 6193, contain- ing around thirty bright stars and for- ming the heart of the Ara OB1 as- sociation. The two brightest stars are very hot giant stars. Together, they provide the main source of illumina- tion for the nearby emission nebula, the Rim Nebula, or NGC 6188, which is visible to the right of the cluster. A stellar association is a large group- ing of loosely bound stars that have not yet completely drifted away from their initial formation site. OB associations consist largely of very young blue–white stars, which are about 100 000 times brighter than the Sun and between 10 and 50 times more massive. The Rim Nebula is the prominent wall of dark and bright clouds marking the boundary between an active star- forming region within the molecular cloud, known as RCW 108, and the rest of the association. The area around RCW 108 is made up of most- ly hydrogen — the primary ingre- T his image, taken by OmegaCAM on the VLT Survey Telescope at Para- nal Observatory, shows a section of the Ara OB1 stellar association. In the centre of the image is the young open cluster NGC 6193, and to the right is the emission nebula NGC 6188, illuminated by the ionising radiation emitted by the brightest nearby stars. [ESO] dient in star formation. Such areas are also known as H II regions. The ultraviolet radiation and intense stellar wind from the stars of NGC 6193 seem to be driving the next gen- eration of star formation in the sur- rounding clouds of gas and dust. As cloud fragments collapse they heat up and eventually form new stars. As the cloud creates new stars, it is simultaneously being eroded by the winds and radiation emitted by pre- vious stars, and by violent superno- va explosions. In this way, such star- forming H II regions tend to have a lifespan of just a few million years. Star formation is a very inefficient process, with only around 10% of the available material contributing to the process — the rest is blown off into space. The Rim Nebula also shows signs of being in the early phase of “pillar formation”, mean- ing that in the future it could end up looking similar to other well-known star-forming regions, such as the Eagle Nebula (Messier 16, contain- ing the famous Pillars of Creation) and the Cone Nebula (part of NGC 2264). This single spectacular image was actually created from more than 500 individual pictures taken through four different colour filters with the VLT Survey Telescope. The total exposure time was more than 56 hours. It is the most detailed view of this region yet achieved. n