When left alone disks galaxies can rearrange their stars and gas (as a response to instabilities).This process (called secular evolution) is often seen as spiral disks and galactic bars.

• 当分离后，有盘的星系可能会重整它们的恒星和气体 (作为对不稳定状的一种回应)，这种过程 (称为世代演化) 经常在螺旋星系和棒旋星系中观察到。