These are characterized by broad, flat rotating disks of stars, gas, and dust; a central bulge of older, redder stars, sometimes with a long cylindrical or rectangular bar of stars as well; and a huge extended halo of older stars.

它们是由恒星、气体和尘埃组成的宽而平的旋转盘；由较老的、较红的恒星组成的中央凸出部分，有时也有长长的圆柱形或长方形的恒星条，还有一个巨大的古老恒星光晕。