星系自转曲线（Galaxy rotation curve）可以绘制成以恒星或气体的轨道速度为y轴，相对于至核心距离为x轴的图表。 恒星围绕星系核心公转的速度在从星系核新开始的一个大范围的距离内是均速，而且它们的速度比在自由牛顿位能预期的旋转更为快速。

星系自转问题是被观察到的转动速度，和可观测到的螺旋星系质量，以牛顿动力学预测的星系盘部分的速度之间所造成的矛盾。目前认为这一矛盾现象可以经由暗物质和晕的存在与延伸入星系中而予以解决。

The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre. It is typically rendered graphically as a plot.

The rotational/orbital speeds of galaxies/stars do not follow the rules found in other orbital systems such as stars/planets and planets/moons that have most of their mass at the centre. Stars revolve around their galaxy's centre at equal or increasing speed over a large range of distances. Instead, the orbital velocity of planets in solar systems and moons orbiting planets decline with distance. In the latter cases, this reflects the mass distributions within those systems. The mass estimations for galaxies based on the light they emit are far too low to explain the velocity observations.