Now that celebrations are underway for Hubble's 25th anniversary, it's the perfect time to revisit what many consider to be Hubble's most iconic target: the Andromeda Galaxy. In addition to being one of the largest and brightest galaxies in our local group, it's also the closest, lurking just 2.5 million light-years from Earth (in a constellation of the same name).
This new image is the sharpest view yet of Andromeda (otherwise known as Messier 31); it also happens to be the largest image ever assembled using data from Hubble; it's so sharp, in fact, that, despite the distances involved, individual stars can be resolved within a 61,000 light-year cone in Andromeda. NASA likens it to photographing a beach and resolving individual grains of sand (the story is almost as impressive as the one behind Hubble's Ultra Deep Field).
Overall, Andromeda boasts over one trillion stars (more than twice the amount the Milky Way has), all packed within roughly 200,000 light-years of spacetime. Naturally, its nucleus is the most densely-packed part of the galaxy; it also harbors a black hole that weighs more than 30 million Suns combined.
In this particular frame of view, approximately 100 million stars can be seen, most are concentrated in the disk. The image itself combines 7,398 exposures, taken over 411 individual observation periods.
According to NASA,
Explore a zoomable image here.