Stars make a bigger mess in old galaxies, and scientists just figured out why 

 More evolved galaxies demonstrate a greater range of stellar motions compared to the orderly, circular orbits of stars like our sun in the Milky Way. 

https://cdn.mos.cms.futurecdn.net/R5kiJEwDvbPhhKaiPnZ4eV.jpg

https://www.space.com/why-stars-make-bigger-messes-old-galaxies