“He who would search for pearls must dive below.” -John Dryden
If you want to know what types of stars are found all throughout a galaxy, looking at our own simply won't do: too much of it is obscured by the plane and our position within it. But there's an even more impressive galaxy -- Andromeda -- just 2.5 million light years away. And thanks to the power of the Hubble Space Telescope, we've not only resolved individual stars within it, we've resolved over a hundred million of them.
But when we look towards the center versus at the outskirts of the disk, or even into the halo, we find something very, very different: older, redder, fainter and less-evolved stars. Even more spectacularly: beyond them, a rich slew of distant galaxies, visible out to distances exceeding a billion light years.
Interesting to note the visibility of other galaxies through Andromeda in the closeup photo, lower right of photo, reddish appearance.