Wow, that is interesting. I bet on the rare occurrence that stars collide at high velocity going opposite directions it is quite spectacular!
NGC 4550 is the Galaxy. Vera Rubin is the astronomer who discovered this double rotation. There was a fellow who predicted such a possibility beforehand. When Rubin contacted him he was somewhat embarrassed because he thought his paper was a silly conjecture. Imagine his surprise and delight that Rubin had actually found one.