Frame-dragging
There are effects that come out of the math of the frame dragging theory. Scientists have tested one where if a small spinning object is orbiting a larger spinning object, the smaller object will slowly adjust its spin axis (the imaginary line which an object rotates around) to align with the larger object's spin axis. This is known as the Lense-Thirring effect. They have tested this theory by having a gyroscope (an object that normally keeps its spin axis the same) orbit the Earth, and seeing its spin axis align with the Earth's.