Stellar spirals throw up new clues on galactic evolution

An international team of astronomers have identified a thick stellar disc in the Andromeda galaxy, which will help them to understand more about how our own Milky Way and other galaxies evolved. The University of Cambridge-led study involved researchers from the UK, US and Europe, and marks the first time that the "thick disc" in Andromeda, which contains old stars, has been identified. The observation will allow astronomers to analyse an area that formed relatively early in Andromeda's evolution, enabling them to look more closely at how galaxies are assembled. This cannot be easily done in our own galaxy, because the equivalent part of the Milky Way is obscured. Most large galaxies, including the Milky Way, are defined by a spiral structure, in which roughly 70% of all the stars are contained within an area that looks like a huge, flat, stellar disc. This structure contains the spiral arms created by regions where star formation is taking place, surrounding a central bulge of old stars at the core of the galaxy. Studies of the Milky Way and other nearby spiral galaxies have shown that these galaxies actually contain two stellar discs - one of which is thicker than the other.