Gravitomagnetic time delay

According to general relativity, a massive spinning body endowed with angular momentum S will alter the space-time fabric around it in such a way that several effects on moving test particles and propagating electromagnetic waves occur. In particular, the direction of motion with respect to the sense of rotation of the central body is relevant because co-and counter-propagating waves carry a "gravitomagnetic" time delay ΔtGM which could be, in principle, be measured if S is known.

Source: Wikipedia — Gravitomagnetic time delay (CC BY-SA 4.0)