Justas a whirlpoolhasmultiplepeaksandtroughs, a densitywavein a galaxyhasmultipleregionsofhighdensity— thebrightspirals— separatedbyregionsoflowerdensity.
About 5 billionyearsfromnow, theMilkyWaywillstarttomergewiththeAndromedaGalaxy, throwingoffthebalanceofangularmomentumandcreatinganeggshape— thebirthof a newerainourgalaxy's history.