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Originally posted by yuklop
Our galaxy - the Milky Way probably had its spirals made by the LMC and SMC satellite galaxies. They create a non even tidal force on our galaxy. If the galaxy started off Elliptical or speroidal then it would have been elongated. However all the matter in our galaxy is gravitationally bound so cannot escape. This causes the elongated shape to rotate with the satellite galaxy around the centre of the elliptical one with matter colse to the edge being pulled round more thus winding the galaxy up into a spiral shape.
What you're describing is birth of star where radiation pressure stops gravity from collecting more matter/mass to star.
Originally posted by zsandmann
This matter becomes massive enough that it fires up like a giant reactor. A galaxy is created. Now the heat being released coupled with incoming debris creates friction which creates spin.
Originally posted by yuklop
Why do galaxies form discs.... its to do with interactions and conservation of angular momentum.