Free Astronomy Magazine November-December 2016

SPACE CHRONICLES iable stars, and the brightness of each RR Lyrae star fluctuates regu- larly. By observing the length of each cycle of brightening and dimming in an RR Lyrae, and also measuring the star’s brightness, astronomers can calculate its distance. (RR Lyrae stars, like some other regular variables such as Cepheids, show a simple re- lationship between how quickly they VISTA finds remains of archaic globular star cluster by ESO A team led by Dante Minniti (Universidad Andrés Bello, Santiago, Chile) and Rodrigo Contreras Ramos (Instituto Milenio de Astrofísica, Santiago, Chile) used observations from the VISTA infra- red survey telescope, as part of the Variables in the Via Lactea (VVV) ESO public survey, to carefully search the central part of the Milky Way. By observing infrared light, which is less affected by cosmic dust than visible light, and exploiting the excellent conditions at ESO’s Paranal Observatory, the team was able to get a clearer view of this region than ever before. They found a dozen ancient RR Lyrae stars at the heart of the Milky Way that were previously unknown. Our Milky Way has a densely populated centre — a feature common to many galaxies, but unique in that it is close enough to study in depth. This discovery of RR Lyrae stars provides compelling evidence that helps astronomers de- cide between two main competing theories for how nuclear bulges form (the nuclear stellar bulge is the compact component in the inner- most regions of the Milky Way, and other galaxies, extending to a size of about 400 light-years). RR Lyrae stars are typically found in dense globular clusters. They are var- T his image, captured with the VISTA infrared survey telescope, as part of the Variables in the Via Lactea (VVV) ESO public survey, shows the central part of the Milky Way. While normally hidden behind obscuring dust, the infrared capabil- ities of VISTA allow to study the stars close to the galactic centre. Within this field of view astronomers detected several ancient stars, of a type known as RR Lyrae. As RR Lyrae stars typically reside in ancient stellar populations over 10 billion years old, this discovery suggests that the bulging centre of the Milky Way likely grew through the merging of primordial star clusters. [ESO/VVV Survey/D. Minniti]