N-Body Problem II by mbostock

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<style>

body {
  background: #000;
}

</style>
<canvas width="960" height="960"></canvas>
<script src="//d3js.org/d3.v4.0.0-alpha.33.min.js"></script>
<script>

var canvas = document.querySelector("canvas"),
    context = canvas.getContext("2d"),
    width = canvas.width,
    height = canvas.height;

var n = 400,
    pi = Math.PI,
    tau = 2 * pi;

var nodes = d3.range(n).map(function() {
  var r = Math.random() * width / 3,
      a = Math.random() * tau,
      x = width / 2 + r * Math.cos(a),
      y = height / 2 + r * Math.sin(a);
  return {
    x: x,
    y: y,
    vx: (height / 2 - y) * 0.006,
    vy: (x - width / 2) * 0.006
  };
});

var force = d3.forceSimulation(nodes)
    .drag(0)
    .alphaDecay(0)
    .force("charge", d3.forceManyBody().strength(0.02))
    .force("center", d3.forceCenter(width / 2, height / 2))
    .on("tick", ticked);

var stroke = d3.scaleLinear()
    .domain([0, 10])
    .range(["magenta", "yellow"]);

function ticked() {
  context.clearRect(0, 0, width, height);
  context.lineWidth = 4;
  context.lineCap = "square";

  for (var i = 0, node, vx, vy; i < n; ++i) {
    node = nodes[i];
    context.beginPath();
    context.moveTo(node.x, node.y);
    context.lineTo(node.x + node.vx * 3, node.y + node.vy * 3);
    context.strokeStyle = stroke(node.vx * node.vx + node.vy * node.vy);
    context.stroke();
  }
}

</script>