I’ve been saving this one for a few months, specifically for my Halloween post! This was such an interesting story, it was hard for me to pass it up before.  There are ghosts in these distant galaxies! Look at the images above, and see the ghostly green figures.  They are ionized Oxygen, helium, nitrogen, sulphur, and neon that has absorbed high energy radiation and slowly re-emitted it over thousands of years.  The photoionized gas clouds in the images are tens of thousands of light years outside their host galaxies, so where did this high energy radiation come from? The answer, is...