Following LIGO's treasure maps

Astronomers around the world are looking for visible sources of gravitational waves. On the morning of September 16, 2015, an email appeared in 63 inboxes scattered around the globe. The message contained a map of the cosmos and some instructions, and everyone who received it knew the most important thing was to keep it secret. It wasn't until five months later that the world found out what the owners of those inboxes knew: that two days earlier, on September 14, the Laser Interferometer Gravita...