An international team of astronomers has identified for the first time a thick stellar disc in the Andromeda Galaxy, a large spiral galaxy closest to our own Milky Way.
The discovery of the thick disk is the main result of 5 years of research that will help astronomers better understand the processes involved in the formation and evolution of large spiral galaxies like our own. This was reported by a research team consisting of an astronomer at the University of California in Los Angeles, Michael Rich and colleagues from Europe and Australia.
Using the Keck Telescope in Hawaii, the astronomers analyzed the velocities of individual bright stars in the Andromeda galaxy and were able to observe a group of stars in the thick disk - clearly distinguishable from already known to the thin disk of the galaxy - and assessed how these stars differ from stars with thin disk height , width and chemical composition.
Approximately 70% of the stars of Andromeda kept on a thin stellar disk of the galaxy. This disc structure contains the spiral arms of the marked regions of active star formation, and it surrounds a central bulge of old stars in the center of the galaxy.
"From observations of our own Milky Way and other nearby spirals, we know that these galaxies typically possess two stellar discs, as ’thin’ and ’thick’ - said Michelle Collins of the University of Cambridge’s Institute of Astronomy, who led the analysis. Thick disc is formed of stars, which are usually much older than those in the thin disk, allowing you to make a perfect study of galactic evolution.
"The classical thin stellar discs that we typically see in Hubble images are the result of actions, ranging from the accumulation of gas by the end of galaxy formation, whereas thick discs are produced in a much earlier phase of the galaxy’s life, making them ideal for devices that looking for processes of evolution of the galaxy "- said Collins.
The process of formation of thick disks are not yet fully understood. First the best way to understand this structure was to study the thick disk represented in our own Milky Way. However, most of the thick disk of our galaxy, obscured and hidden from view. The discovery of a similar thick disc in Andromeda presents a much clearer view of spiral structure. Astronomers can determine the properties of the disc across the galaxy and will search for traces of events related to his education.
"Our initial study of this component already suggests that it is probably much older than the thin disk, and has a different chemical composition" - said Rich, who was the chief investigator in the Keck Observatory. "In the future, more detailed observations should enable us to understand the formation of the Andromeda disk system, with the potential to apply this understanding to the formation of spiral galaxies throughout the universe."
"This is one of the amazing results of many observations of the movements and the chemical composition of stars in the Andromeda Galaxy’’ - said Scott Chapman of the Institute of Astronomy at Cambridge." Finding this thick disc has allowed us to obtain a unique and grand views of the Andromeda system of education and certainly helped our understanding of this complex process. "