As I’ve mentioned more than once here on the blog, spiral galaxies have a number of components: a flat disk with spiral arms, a central bulge of old stars, a halo surrounding them of old stars, and a bigger halo of dark matter (the invisible stuff that we know exists due to its gravity, which influences the galaxy inside it).
Spirals come in many sizes, too. The Milky Way, our home galaxy, is 100,000 or so light years across. There’s not a clean cutoff; it’s not like there’s a sign that says "end of galaxy" 50,000 light years from the center. Some stars have been detected farther out, but the disk kinda fades into the halo out there.
Many spirals are smaller, half the size of ours. The Large Magellanic Cloud, a satellite companion to the Milky Way, is about 30,000 light years across, and is vaguely spiral.
The Milky Way is big for a galaxy… but there are some that are bigger. A lot bigger.
Like, a whole lot bigger. Seriously, reading this paper about them had me muttering “holy crap” over and again.
These galaxies are called super spirals, and a survey of 53 of them shows they ...