Hello, Andromeda. We’ve never seen you quite like this before.
This wide view of the spiral galaxy closest to our own is 61,000 light-years long and includes more than 100 million stars. It’s the largest image ever assembled from data from NASA’s Hubble Space Telescope, which has worked in space for 25 years. The image is a mosaic of photographs taken with a visible-light camera, so it shows what Andromeda would look like if you could go see it for yourself. The Panchromatic Hubble Andromeda Treasury (PHAT) project also takes images in near-ultraviolet and near-infrared light for scientists to analyze.
On the left of the image, you can see densely packed stars in Andromeda’s central hub. Toward the right is Andromeda’s outer disk. Groups of blue dots indicate young stars and star clusters, where stars are still forming. Dark spots in the picture are dust structures. The underlying reddish color in the image comes from cooler, older red stars found throughout the galaxy.
Hubble is powerful enough to resolve individual stars in Andromeda, allowing scientists to study a star in its natural context of a galaxy. You can get a starting sense of that if you check out the zoomable version of the Andromeda panorama, released yesterday, here.