Free Astronomy Magazine November-December 2015

Cosmic recycling by ESO D eeply immersed in this huge stellar nursery are three clus- ters of hot young stars — only a few million years old — which glow brightly in ultraviolet light. It is the light from these stars that causes the nebula’s gas clouds to glow. The radiation strips electrons from atoms — a process known as ionisation — and when they recombine they re- lease energy in the form of light. Each chemical element emits light in characteristic colours and the large clouds of hydrogen in the nebula are the cause of its rich red glow. Gum 56 — also known as IC 4628 or by its nickname, the Prawn Nebula — is named after the Australian astronomer Colin Stanley Gum, who, in 1955, published a catalogue of H II regions. H II regions such as Gum 56 are huge, low density clouds con- taining a large amount of ionised hydrogen. A large portion of the ionisation in Gum 56 is done by two O-type stars, which are hot blue– white stars, also known as blue gi- ants because of their colour (note that these stars fall outside the field of view of this particular image and do not appear in the picture). This type of star is rare in the Uni- verse as the very large mass of blue giants means that they do not live for long. After only roughly a mil- lion years these stars will collapse in on themselves and end their lives as supernovae, as will many of the other massive stars within the neb- ula. Besides the many newborn stars nestled in the nebula, this large re- gion is still filled with enough dust and gas to create an even newer generation of stars. The regions of the nebula giving birth to new stars are visible in the image as dense clouds. The material forming these new stars includes the remains of the most massive stars from an older generation that have already ended their lives and ejected their material in vio- lent supernova explo- sions. Thus the cycle of stellar life and death continues. Given the two very un usual blue giants in this area and the prominence of the nebula at infrared and radio wavelengths, it is perhaps surprising that this region has been comparatively little studied as yet by professional astrono- mers. Gum 56 has a diame- ter of around 250 light- years, but despite its huge size it has also often been overlooked by visual ob- servers due to its faintness, and because most of the light it emits is at wave- lengths not visible to the human eye. The nebula is at a distance of about 6000 light-years from Earth. In the sky it can be found in the constella- tion Scorpius (The Scorpion) where it has a projected size which is four times the size of the full Moon. This image, which only cap- tures a part of the nebula, was taken with the 2.2- metre MPG/ESO telescope using the Wide Field Imager (WFI) camera as part of the ESO Cosmic Gems pro- gramme. The programme makes use of telescope time that cannot be used for science observations to pro- duce images of interesting, intriguing or visually attrac- tive objects. All data col- lected may also be suitable for scientific purposes, and are made available to as- tronomers through ESO’s science archive. T he rich patchwork of gas clouds in this new image make up part of a huge stellar nurs- ery nicknamed the Prawn Nebula (also known as Gum 56 and IC 4628). Taken using the MPG/ ESO 2.2-metre telescope at the La Silla Obser- vatory in Chile, this may well be one of the best pictures ever taken of this object. It shows clumps of hot new-born stars nestled in among the clouds that make up the nebula. [ESO] T his video sequence starts with a view of the rich central parts of the Milky Way and then closes in on a spectacular region of star forma- tion known as the Prawn Nebula (also known as Gum 56 and IC 4628) in the constellation of Scorpius (The Scorpion). The final close up view is a very sharp image taken using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observa- tory in Chile. [ESO/Nick Risinger (skysurvey.org)] n