And the fix, it turns out, is not some exotic new sensor, but a thermal camera you could genuinely buy off the shelf. LIGO detects gravitational waves, ripples in spacetime thrown off by colliding black holes and neutron stars, by watching for impossibly tiny changes in distance along its four kilometre arms. The trouble is, even LIGO's mirrors, among the purest optical components ever manufactured, absorb a sliver of that light. Only afterward did they realise that surface temperature readings, combined with a good thermal model, could reveal the internal distortion on their own. Source : New technique enables LIGO to peer farther into the distant universe