Free Astronomy Magazine November-December 2016

SPACE CHRONICLES Davide Massari, co-author of the study, from INAF, Italy, and the Uni- versity of Gröningen, Netherlands. Its unusual properties make Terzan 5 the ideal candidate for a living fossil from the early days of the Milky Way. Current theories on galaxy forma- keep existing embedded within the galaxy,” explains Francesco Ferraro from the University of Bologna, Italy, and lead author of the study. “Such galactic fossils allow astronomers to reconstruct an important piece of the history of our Milky Way.” While the properties of Terzan 5 are uncommon for a globular cluster, they are very similar to the stellar population which can be found in the galactic bulge, the tightly packed central region of the Milky Way. These similarities could make Terzan 5 a fossilised relic of galaxy formation, representing one of the earliest building blocks of the Milky Way. This assumption is strength- ened by the original mass of Terzan 5 necessary to create two stellar populations: a mass similar to the huge clumps which are assumed to have formed the bulge during galaxy assembly around 12 billion years ago. Somehow Terzan 5 has managed to survive being disrupted for billions of years, and has been preserved as a remnant of the dis- tant past of the Milky Way. “Some characteristics of Terzan 5 re- semble those detected in the giant clumps we see in star-forming gal- axies at high-redshift, suggesting that similar assembling processes occurred in the local and in the dis- tant Universe at the epoch of gal- axy formation,“ continues Ferraro. Hence, this discovery paves the way for a better and more complete un- derstanding of galaxy assembly. “Terzan 5 could represent an in- triguing link between the local and the distant Universe, a surviv- ing witness of the Galactic bulge as- sembly process,” concludes Ferraro while commenting on the impor- tance of the discovery. The research presents a possible route for astron- omers to unravel the mysteries of galaxy formation, and offers an un- rivaled view into the complicated history of the Milky Way. n tion assume that vast clumps of gas and stars interacted to form the pri- mordial bulge of the Milky Way, merging and dissolving in the pro- cess. “We think that some remnants of these gaseous clumps could re- main relatively undisrupted and P eering through the thick dust clouds of the galactic bulge an international team of astronomers has revealed the unusual mix of stars in the stellar cluster known as Terzan 5. The new results indicate that Terzan 5 is in fact one of the bulge's primordial building blocks, most likely the relic of the very ear- ly days of the Milky Way. [NASA/ESA/Hubble/F. Ferraro]