Comment by maxnoe

We know this because

- In the beginning, for the first couple of events, only because they have way higher energies than anything in the solar system could produce - By now, with enough data collected, their origin correlates very well with the milky way - we are close to identifying several far away galaxies as well

This is the significance. Contrary to some statements published today, IceCube was not primarily built to study Neutrinos, it was built to study the universe using Neutrinos.

That's why we care where they are coming from, we want to learn about the astrophysical objects that produce them.