Free Astronomy Magazine March-April 2015

MARCH-APRIL 2015 SPACE CHRONICLES T his zoom video sequence goes from a wide view of the southern Milky Way deep into the constellation of Puppis close to the site of the Vela supernova remnant. The final view shows a new close-up view of the cometary globule CG4. It glows menacingly, like the gaping mouth of a gigantic celestial creature, in this new image from ESO’s Very Large Telescope. What looks huge and bright in this image is actually a faint nebula and not easy to observe. The exact na- ture of CG4 remains a mystery. [ESO/J.Perez/Digitized Sky Survey 2/N. Risinger] The head part of CG4 is a thick cloud of gas and dust, which is only visible because it is illuminated by the light from nearby stars. The radiation emitted by these stars is gradually destroying the head of the globule and eroding away the tiny particles that scatter the starlight. However, the dusty cloud of CG4 still contains enough gas to make several Sun- sized stars and indeed, CG4 is actively forming new stars, perhaps triggered as radiation from the stars powering the Gum Nebula reached CG4. Why CG4 and other cometary glob- ules have their distinct form is still a matter of debate among astrono- mers and two theories have develop- ed. Cometary globules, and therefore also CG4, could originally have been spherical nebulae, which were dis- rupted and acquired their new, un- usual form because of the effects of a nearby supernova explosion. Other astronomers suggest, that cometary globules are shaped by stellar winds and ionising radiation from hot, mas- sive OB stars. These effects could first lead to the bizarrely (but appropri- ately!) named formations known as elephant trunks and then even- tually cometary globules. To find out more, astronomers need to find out the mass, density, tempe- rature, and velocities of the material in the globules. These can be deter- mined by the measurements of mo- lecular spectral lines which are most easily accessible at millimetre wave- lengths — wavelengths at which telescopes like the Atacama Large Millimeter/submillimeter Array op- erate. This picture comes from the ESO Cosmic Gems programme, an out- reach initiative to produce images of interesting, intriguing or visually at- tractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observa- tions. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive. n