Free Astronomy Magazine September-October 2015

SEPTEMBER-OCTOBER 2015 SPACE CHRONICLES enon, lasting only a few tens of thou- sands of years, compared to a typi- cal stellar lifetime of several billion years. The lifetime of a planetary nebula as a fraction of a star's life is about the same as the life of a soap bubble compared to the age of the child who blows it. Planetary nebulae are created by the ejected and expanding gas of dying stars. Although they are bril- liant and intriguing objects in the initial stages of formation, these bubbles fade away as their constit- uent gas moves away and the cen- tral stars grow dimmer. For a planetary nebula to form, the aging star must have a mass less than about eight times that of the Sun. Stars that are heavier than this limit will end their lives in dramatic fashion as supernova explosions. As these less massive stars grow old they start to lose their outer layers of gas to stellar winds. After most of these outer layers have dissi- pated, the remaining hot stellar core starts to emit ultraviolet radia- tion which then ionises the surrounding gas. This ionisation causes the expanding shell of ghostly gas to begin to glow in bright colours. After the planetary neb- ula has faded away, the leftover stellar remnant will burn for another billion years before con- suming all its remaining The ghost of a dying star by ESO N icknamed the Southern Owl Nebula, this shimmering orb is a planetary nebula with a diameter of almost four light-years. Its informal name relates to its vi- sual cousin in the northern hemi- sphere, the Owl Nebula. ESO 378-1, which is also catalogued as PN K 1- 22 and PN G283.6+25.3, is located in the constellation of Hydra, the Fe- male Water Snake. (The ESO in the name of this object refers to a cata- logue of objects compiled in the 1970s and 80s from careful inspec- tion of new photographs taken with the ESO 1-metre Schmidt tele- scope at La Silla.) Like all planetary nebulae, ESO 378- 1 is a relatively short-lived phenom- T his video sequence starts from a wide field of the Milky Way and closes in on a rather empty patch of sky in the huge constellation of Hydra. A strange blue disc becomes visible — the planetary nebula ESO 378-1. The final very detailed view comes from ESO’s Very Large Telescope at the Paranal Observatory in Chile. [ESO/Digitized Sky Survey 2/N. Risinger]