Free Astronomy Magazine March-April 2015

SPACE CHRONICLES T his small extract from the VISTA VVV survey of the central parts of the Milky Way (previuos page and above) shows the famous Trifid Ne- bula to the right of centre. It appears as faint and ghostly at these infrared wavelengths when compared to the familiar view at visible wavelengths. This transparency has brought its own benefits - many previously hidden background objects can now be seen clearly. Among these are two newly discovered Cepheid variable stars, the first ever spotted on the far side of the galaxy near its central plane. The positions of the faint Cepheids are marked on this annotated version. [ESO/VVV consortium/D. Minniti] where it glows brightly in both the pink emission from ionised hydro- gen and the blue haze of scattered light from hot young stars. Huge clouds of light-absorbing dust are also prominent. But the view in the VISTA infrared picture is very dif- ferent. The nebula is just a ghost of its usual visible-light self. The dust clouds are far less prominent and the bright glow from the hydrogen clouds is barely visible at all. The three-part structure is almost invisi- ble. In the new image, as if to com- pensate for the fading of the ne- bula, a spectacular new panorama comes into view. The thick dust clouds in the disc of our galaxy that absorb visible light allow through scope at ESO’s Paranal Observatory in Chile is mapping the central re- gions of the Milky Way in infrared light to search for new and hidden objects. This VVV survey (standing for VISTA Variables in the Via Lac- tea) is also returning to the same parts of the sky again and again to spot objects that vary in brightness as time passes. A tiny fraction of this huge VVV dataset has been used to create this striking new picture of a famous object, the star formation region Messier 20, usually called the Trifid Nebula, because of the ghostly dark lanes that divide it into three parts when seen through a telescope. The familiar pictures of the Trifid show it in visible light,