The blue ring was formed after the galaxy on the left passed through the galaxy on the right. Just as a pebble thrown into a pond creates an outwardly moving circular wave, or ripples, an outwardly propagating ring of higher density was generated at the point of impact of the two galaxies. As this excess density collided with outer material that was moving inwards due to the gravitational pull of the two galaxies, shocks and dense gas were produced, stimulating star formation.
I wonder why the effects of the passage were so unequally distributed.
And it's just as well that Doc Smith didn't know about this, or the beautiful intro for the Lensman series, which has galaxies that pass through each other creating planets, might not have happened.
Link thanks to atomicat
Ten things you don't know about black holes
Actually, I knew a couple of them, but....
Matter falling into a black hole would rarely if ever just fall straight in and disappear. If it has a little bit of sideways motion it’ll go around the black hole. As more matter falls in, all this junk can pile up around the hole. Because of the way rotating objects behave, this matter will create a disk of material whirling madly around the hole, and because the gravity of the hole changes so rapidly with distance, matter close in will be orbiting much faster than stuff farther out. This matter literally rubs together, generating heat through friction. This stuff can get really hot, like millions of degrees hot. Matter that hot glows with intense brightness… which means that near the black hole, this matter can be seriously luminous.
I'd heard of accretion disks, but I didn't know how they work.
I wish there were someone writing science fiction based on current astronomy. Afaik, Poul Anderson used to do that sort of thing, but no one else has specialized in it since.
And I miss Kelly Freas' work. That ring of blue white stars is pure Freas.