Science Buddies: "Ask an Expert"

I have science homework to complete in the next hour, if it's not done i fail class, can someone please help me answer the following question which is worth 3 marks.
' What is a Galaxy comprised of? What forces keep a Galaxy rotating? What must happen to this force if it to hold larger mass objects in orbit? '
THANKYOU

Hello. This forum is to help students with science fair projects. There are other, more appropriate forums for homework help. Good luck!