Notes:
A Spiral Galaxy
In this image we can clearly see two distinct populations of stars within this typical spiral galaxy, the bluer stars and the redder stars (colour contrast has of course been increased). The bluer stars are hotter, high mass stars, which live relatively short lives and so must be young, recently formed in the spiral arms of the galaxy. The redder stars are cooler, low mass stars, which live long lives and these are typically found in the centre of the galaxy, around its nucleus. Therefore there is little star formation going on in the centre of the galaxy, but lots of ongoing formation in the spiral arms.
Furthermore, another interesting scientific paradigm demonstrated by this image is that of the gravitational effect of the spiral galaxy’s companion galaxy here pulling the stars of the spiral galaxy in towards itself.