Whether an entire galaxy becomes a disk is a timing issue: spiral galaxies emerge from gas that becomes rotationally supported before patches of the gas contract into stars.

• 至于整个星系变成一个圆盘则是时机问题：螺旋星系的出现，是因为在每一小团气体因收缩而形成恒星前，整团气体已经成为旋转性支撑。