The phrase "gravitational tug" refers to the force of attraction that an object with mass has on another object. It is like a pull that makes objects move towards each other in space. Full definition
A stronger gravitational tug means that something very dense is beneath the surface; a weaker tug indicates something lighter and less dense. (latimes.com)
The first method detects planets by the subtle gravitational tug they give to their host stars. (keckobservatory.org)
Such wobbles are caused by the back - and - forth gravitational tugs of planets circling around them. (discovermagazine.com)