Free Astronomy Magazine September-October 2019

20 SEPTEMBER-OCTOBER 2019 SPACE CHRONICLES by IAC The early days of the Milky Way revealed by Gaia E arly days of the Milky Way, artist impression. [Gabriel Pérez Díaz, SMM (IAC)] T he universe 13 billion years ago was very different from the universe we know today. It is understood that stars were forming at a very rapid rate, forming the first dwarf galaxies, whose mergers gave rise to the more massive present-day galaxies, including our own. However, the exact chain of the events which produced the Milky Way was not known until now. Exact measurements of position, brightness and distance for around a million stars of our galaxy within 6,500 light-years of the Sun, ob- tained with the Gaia space tele- scope, have allowed a team from the IAC to reveal some of its early stages. “We have analyzed, and compared with theoretical models, the distri- bution of colours and magnitudes (brightnesses) of the stars in the Milky Way, splitting them into sev- eral components, the so-called stel- lar halo (a spherical structure which surrounds spiral galaxies) and the thick disc (stars forming the disc of our Galaxy, but occupying a certain height range)” , explains Carme Gal- lart, a researcher at the IAC and the