What changes are being made to VIRGO and LIGO (if any)? Gravitational wave detectors VIRGO and LIGO are currently down for some updates, slated to be completed sometime early next year (they hope). What exactly are they doing? I hadn't heard it was down again after the last set of updates awhile ago. What are they updating now-- is that knowledge public domain?

Source: I went to an astronomy club meeting and it was stated in the presentation.
Currently, LIGO and Virgo are in what's known as a commissioning phase, a scheduled stage where the teams work on improving the sensitivity of the detectors. A big part of this is noise reduction, but there are other technical updates (an evolving plan also mentions increasing the power of the lasers and adding a "squeezed vacuum source"). Virgo in particular is replacing the steel fibers that hold up their mirrors with silica ones. The original silica fibers failed and were replaced with steel ones before last year's detection of GW170817, but now new silica ones are being added.

As of October, the Livingston site has reached low noise levels, while Hanford is still a bit away. Virgo isn't quite there yet. Soon, though, the three detectors should begin a couple of joint engineering runs, testing the hardware updates before O3 (the third, year-long, observing session) begins in February.