OptionalcallbacksCentring pull toward the canvas centre, applied only to isolated (degree-0) nodes so they don't fly off; connected nodes use d3GravityStrengthConnected.
Centring pull for connected nodes. Kept low by default so link + charge forces find their own equilibrium; raise it to stop a sparsely-linked graph from drifting apart.
Remarks
These may be scalled based on the amount of node and canvas size