When people talk about sunspots and the solar cycle and stuff like that, they often mention magnetic field lines poking through the surface of the sun. I'm pretty sure I get why the magnetic field lines would be twisted up by the non-uniform rotation of the sun, and why they would poke out of the surface. What I totally *do not* get, is how the heck a magnetic field line *breaks*. This seems to me that it would mean that magnetic field lines are physical things... or rather that they are "made of something", like some kind of material. I just don't have any sort of idea of how a magnetic field line could be broken based on my understanding of what a field line is. Is this something that I will learn about in E&M courses?