Thick disc of older stars discovered in nearby Andromeda galaxy
By ANIWednesday, February 16, 2011
WASHINGTON - Scientists have identified for the first time a thick stellar disc in the Andromeda galaxy, the nearest large spiral galaxy to our own Milky Way.
According to an international team of astronomers, who conducted the study, the finding will lead to better understanding of the processes involved in the formation and evolution of large spiral galaxies like ours.
The team includes UCLA research astronomer Michael Rich and colleagues from Europe and Australia.
Using the Keck Telescope in Hawaii, the astronomers analyzed the velocities of individual bright stars within the Andromeda galaxy and were able to observe a group of stars tracing a thick disc - distinct from those comprising the galaxy’s already-known thin disc - and assessed how these stars differ from thin-disc stars in height, width and chemistry.
Approximately 70 percent of Andromeda’s stars are contained in the galaxy’s thin stellar disc. This disc structure contains the spiral arms traced by regions of active star formation, and it surrounds a central bulge of old stars at the core of the galaxy.
“From observations of our own Milky Way and other nearby spirals, we know that these galaxies typically possess two stellar discs, both a ‘thin’ and a ‘thick’ disc,” said Michelle Collins, a doctoral student at the University of Cambridge’s Institute of Astronomy, who led the study.
The thick disc consists of older stars whose orbits take them along a “thicker” path - one that extends both above and below the galaxy’s thin disc.
“The classical thin stellar discs that we typically see in Hubble imaging result from the accretion of gas towards the end of a galaxy’s formation, whereas thick discs are produced in a much earlier phase of the galaxy’s life, making them ideal tracers of the processes involved in galactic evolution,” Collins said. (ANI)
