More than a year after detecting the first confirmed gravitational waves, researchers were busy at the Laser Interferometer Gravitational-wave Observatory (LIGO) in Livingston, La., upgrading the massive instrument. Building on lessons learned during that historic first run, they expect the improved detector will find more gravitational waves during the second observing run, which began Nov. 30.

LIGO detects gravitational waves by splitting a powerful infrared laser beam in two, then sending the beams at right angles through tunnels to mirrors 2.5 miles away. The beams are recombined upon return. A gravitational wave will warp space and briefly change the relative distance between the mirrors and photo detector situated near the LIGO control room. The difference is astonishingly small, just 1/10,000 of a proton’s diameter, but it can be detected if the mirrors are isolated from all external sources of vibration.

Discover photo editor Ernie Mastroianni visited the facility in November as physicists and engineers were calibrating equipment.