There's powerful wizardry at work here...

Well, my vortex disappeared after the game crashed. But it was cool to have it, especially when the character walked into it.

I haven't remote-fed any of my mons though, and I only have one left in a gym that was still standing last I checked.
Also, sometimes the vortex appears when I'm catching pokemon. But this is the first time it spawned in the world view.