In the rather excellent We Are Legion (We Are Bob) - Dennis E. Taylor (Goodreads), Bob jokingly says, "Hey, with IPv8, we should be able to address every galaxy in the universe." Given Bob's situation at the time, one would expect him to be able to work that out pretty quickly. But how right was he?
The European Space Agency (ESA) estimates that there are between 10^11 and 10^12 galaxies in the universe. Since we're comparing numbers of stars to numbers of addresses on the internet, we should convert our number to a power of two. We're also stress-testing the internet protocol with this post, so we'll pick the upper bound of the ESA's estimation.
10^12 = 2^39.8631 ~= 2^40 galaxies in our universe.
The ESA continues with the estimate that there are also between 10^11 and 10^12 stars in our galaxy. We will then assume that our galaxy is pretty average—that is that all other galaxies contain the same-ish number of stars.
10^12 x 10^12 = 10^24 stars in our universe
Again, we convert that number to a power of two.
10^24 = 2^79.7263 ~= 2^80 stars in our universe
Since IPv6 allocates 2^128 addresses, Bob won't even need to write the RFC for IPv8!