Centaurus A not only has a terrifying name, it's our nearest "giant galaxy," only 13 million light years away. Its superluminous central area comes from a supermassive black hole, and it's already swallowing a neighboring spiral galaxy. How long before it comes and pwns us?
Okay, probably not any time soon. But I still think we should build a security fence or something around our galaxy — maybe out of antimatter. I saw in Angels And Demons that it's easy to make lots of antimatter, and if you can put it in a suitcase, you ought to be able to build a wall out of it. [European Southern Observatory]