And by gigantic, I mean it's bigger than our Galaxy.
It is beyond the scale of the scale of the scale that we consider big. Just the hole in the center of it is 16k light years across. That's 10,000,000,000,000,000, or ten quadrillion miles. QUADRILLION.
SOMEONE WRITE A SONG ABOUT THIS FUCKIN' THING. (inb4 'its almost as your mom')
The scientists say the green is gas interacting with energy from a supermassive blackhole or something, but they be lyin' bitches, so what do YOU think it is?
I reckon it's either the Tyranid main fleet, or Necron fuckery