Comparing the GW170104 signal seen by LIGO (in blue and orange) with computer simulations of black hole mergers (in black). The black circles represent the simulated black holes, scaled in proportion to their masses. Black holes can also spin about an axis, and where a simulated black hole was spinning we show the direction of the north pole with a gray arrow. The longer the arrow, the faster the spin. Interestingly, all of the simulations produce results broadly similar to the detected signal, despite their different configurations.