Free Astronomy Magazine November-December 2016

SPACE CHRONICLES change in bright- ness and how lumi- nous they are. Lon- ger periods mean brighter stars. This period-luminosity relationship can be used to deduce the distance of a star from its period of variation and its ap- parent brightness.) Un f o r t u n a t e l y, these excellent dis- t an c e - i nd i c a t o r stars are frequently outshone by youn- ger, brighter stars and in some re- gions they are hid- den by dust. Therefore, locating RR Lyrae stars right in the extremely crowded heart of the Milky Way was not possible until the public VVV sur- vey was carried out using infrared light. Even so, the team described the task of locating the RR Lyrae stars in amongst the crowded throng of brighter stars as “daunting”. Their hard work was rewarded, how- ever, with the identification of a doz- en RR Lyrae stars. Their discovery in- dicate that remnants of ancient glob- ular clusters are scattered within the centre of the Milky Way’s bulge. T his visible light wide-field view shows the rich star clouds in the constel- lation of Sagittarius (the Archer) in the di- rection of the centre of our Milky Way galaxy. The entire im- age is filled with vast numbers of stars — but far more remain hidden behind clouds of dust and are only revealed in infrared images. This view was created from photographs in red and blue light and forming part of the Digitized Sky Survey 2. The field of view is approximately 3.5 de- grees x 3.6 degrees. [ESO and Digitized Sky Survey 2. Ack- nowledgment: Davide De Martin and S. Gui- sard ( www.eso.org/ ~sguisard)] Rodrigo Contreras Ramos elabo- rates: “This discovery of RR Lyrae Stars in the centre of the Milky Way has important implications for the formation of galactic nuclei. The evidence supports the scenario in which the nuclear bulge was origi- nally made out of a few globular clusters that merged.” The theory that galactic nuclear bulges form through the merging of globular clusters is contested by the com- peting hypothesis that these bulges are actually due to the rapid accre- tion of gas. The unearthing of these RR Lyrae stars — almost always found in glob- ular clusters — is very strong evi- dence that part of the Milky Way's nuclear bulge did in fact form through merging. By extension, all other similar galactic bulges may have formed the same way. Not only are these stars powerful evidence for an important theory of galactic evolution, they are also likely to be over 10 billion years old — the dim, but dogged survivors of perhaps the oldest and most mas- sive star cluster within the Milky Way. T he video, based on observations made in the infrared with the VISTA infrared survey telescope shows the central region of the Milky Way galaxy. Several variable stars within the field of views are marked with circles. They can also be identified as they brighten and fade in regular inter- vals. At the end the video zooms on one of the newly discovered RR Lyrae stars (marked with a red circle), which are too faint to be seen clearly in the large field of view. [ESO/VVV Survey/D. Minniti] n