Of course, a “magma galaxy” doesn’t make much sense if taken literally. Space is pretty cold. Magma is pretty hot. Also, magma only exists under a planet’s crust. So it would solidify pretty fast and not really be magma in any sense of the word. It’s a good thing that this is abstract art and not, like, supposed to be a literal representation of something that could exist! You can say that this galaxy is actually made up of some other form of matter with properties similar to magma, but nothing that we’ve discovered yet. That way, comparing it to magma is a good way to get across how it behaves. Maybe it’s dense neutronium-infused ions. Perhaps it’s tau electrons interacting with photonic matter. Maybe it’s the nineteenth flavor of neutrinos.
Y’know, whatever sciencey words you want. Feel free to make stuff up for your friends when you show it to them. As long as it’s sufficiently advanced sounding buzzwords chained together, I’ll totally endorse it. Bonus points if you add in words implying radiation or momentum. After all, we’ve clearly got some glowy stuff going on here, and all kinds of motion on a massive scale in multiple directions. So you can make a case for your explanation regardless of what it is. What kind of spacecraft could explore this? How would it border “regular” space and what would that border look like, and what would crossing it feel like? Here’s a close-up:
You can buy this multicolored volcanic galactic piece in multiple sizes, canvas or metal prints, phone cases, tapestries, whatever. Go wild. I promise it will not drip molten fluid onto your floor unless you superheat it yourself, which I guess you can have fun with if you want. Here it is in full: