On Aug. 14, 2019, a gravitational wave -- a massive ripple through the fabric of space-time -- washed over the Earth. The signal was one of the strongest ever seen by the gravitational wave scientists at the Laser Interferometer Gravitational-wave Observatory and Italy's Virgo observatory. After an alert was sent out moments after detection, teams of astronomers across the world turned their telescopes to the point in space that the wave emanated from. But their searches came up empty. No light, no X-rays, no infrared, no gamma rays. On Tuesday, researchers from the LIGO and Virgo collaborations detail their full...