Free Astronomy Magazine July-August 2020

27 JULY-AUGUST 2020 GALAXIES young Milky Way. As is easy to imagine, the merging of the two galaxies was a slow and gradual process, nevertheless capable of triggering a star formation burst which, gradually decreasing, kept on for about four billion years. At the end of that process, the residual gas and dust entered the thin disk of the Milky Way. The cannibalization of Gaia-Enceladus is the most relevant event of its kind still recogniz- able, but not the last for which there re- mains a trace. Other star formation bursts have also been recognized, albeit less in- tense and more remote. However, until a few years ago, it was practically impossible go back to find the cause of those events. In order to do this, it is essential to know at least some fundamen- tal properties (bright- ness, color, position, distance, direction of motion, speed) of nu- merous stars spread across a very signifi- cant fraction of the Milky Way. If the sam- pling is done in a too- narrow region, say in a sphere with a radius of a few hundred A bove and in the video below we see the reconstruction of the dynamics of the Gaia-Ence- ladus event. Note that the current form of the Milky Way is also the result of minor interactions caused by small satellite galaxies. [Gabriel Pérez Díaz/SMM (IAC)] still recognizable through the different dy- namic and physical properties that the two sets of original stars show. Many studies have indeed highlighted that our galaxy is home to two distinct sets of stars, having the same age but different metallicity. The set of stars containing fewer metals (in as- tronomy, all of the elements heavier than hydrogen and helium) were carried by Gaia- Enceladus and are characterized by a chaotic motion. In the billions of years fol- lowing the galactic merger, Gaia-Enceladus stars contributed to building up the halo of the current Milky Way. The dynamically-ti- dier set of stars is the original set of the