Free Astronomy Magazine May-June 2016

SPACE CHRONICLES of an ancient supernova, and the glowing red filaments at the lower left surround an unusual and very hot star. The supernova remnant is SNR G332.4-00.4, also known as RCW 103. It is about 2000 years old. The lower filaments are RCW 104, surrounding the Wolf–Rayet star WR 75. Although these objects bear RCW numbers, detailed later investigations revealed that neither of themwere HII regions. Patches of dark obscuring dust are also visible across the entire cosmic landscape. Astronomers have been studying RCW 106 for some time, al- though it is not the crimson clouds that draw their attention, but rather the mysterious origin of the massive and powerful stars buried within. Al- though they are very bright, these stars cannot be seen in visible-light images such as this one as the sur- rounding dust is too thick, but they make their presence clear in images of the region at longer wavelengths. For less massive stars like the Sun the process that brings them into exis- tence is quite well understood — as clouds of gas are pulled together under gravity, density and tempera- ture increase, and nuclear fusion be- gins — but for the most massive stars buried in regions like RCW106 this ex- planation does not seem to be fully adequate. These stars — known to astronomers as O-type stars — may have masses many dozens of times the mass of the Sun and it is not clear how they manage to gather, and keep to- gether, enough gas to form. O-type The realm of buried giants by ESO I n this huge new image clouds of crimson gas are illuminated by rare, massive stars that have only recent- ly ignited and are still buried deep in thick dust clouds. These scorching- hot, very young stars are only fleeting characters on the cosmic stage and their origins remain mysterious. The vast nebula where these giants were born, along with its rich and fascinat- ing surroundings, are captured here in fine detail by ESO’s VLT Survey Tele- scope (VST) at the Paranal Observa- tory in Chile. RCW 106 is a sprawling cloud of gas and dust located about 12,000 light-years away in the south- ern constellation of Norma (The Car- penter’s Square). The region gets its name from being the 106 th entry in a catalogue of HII regions in the south- ern Milky Way. The catalogue was compiled in 1960 by three astrono- mers from the Mount Stromlo Obser- vatory in Australia whose surnames were Rodgers, Campbell and White- oak, hence the prefix RCW. HII re- gions like RCW 106 are clouds of hydrogen gas that are being ionised by the intense starlight of scorching- hot, young stars, causing them to glow and display weird and wonder- ful shapes. RCW 106 itself is the red cloud above centre in this new image, although much of this huge HII re- gion is hidden by dust and it is much more extensive than the visible part. Many other unrelated objects are also visible in this wide-field VST image. For example, the filaments to the right of the image are the remnants stars likely form from the densest parts of the nebular clouds like RCW 106 and they are notoriously difficult to study. Apart from obscuration by dust, another challenge is the brevity of an O-type star’s life. They burn through their nuclear fuel in mere tens of millions of years, while the lightest stars have lifetimes that span many tens of billions of years. The dif- ficulty of forming a star of this mass,