Bug in vis.network:

When there are nodes with small mass they are pulled relatively stronger to the centre of gravity.
The central force should be proportional to the mass of the node.

In this example node 1 is heavier than node 3 with its satellites. However node 3 with its satellites gets pulled to the centre of gravity.

var nodes = new vis.DataSet([
{ id: 1, label: "Node 1", size: 20, mass: 2},
{ id: 2, label: "Node 2", size: 20, mass: 1},
{ id: 3, label: "Node 3", size: 20, mass: 1},

{ id: 4, shape: "dot", size: 5, mass: 0.1},
{ id: 5, shape: "dot", size: 5, mass: 0.1},
{ id: 6, shape: "dot", size: 5, mass: 0.1},
{ id: 7, shape: "dot", size: 5, mass: 0.1},
]);
var edges = new vis.DataSet([
{ from: 1, to: 2 },
{ from: 2, to: 3 },

{ from: 3, to: 4},
{ from: 3, to: 5 },
{ from: 3, to: 6 },
{ from: 3, to: 7 }
]);