Those of us who are waiting for an alert for a Kilonova triggered by the merger of two neutron stars might have noticed that recently there was a longer pause in gravitational wave alerts. This was caused by one of the LIGO detectors going offline for repairs after a small but crucial part failed : a TOASTR .
We know quite a bit about this because the LIGO observatories maintain logs that are public (I do hope this is intentional…), and these logs list all sorts of problems/repairs/engineering investigations. Anything from wild animals seen on the site to power failures.
See for example:
https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=73576
So what is a TOASTR? Short for “Turbo Optical Anti-Symmetric Transient Rejector”, you can think of it as a high speed optical circuit-breaker: if sensors detect that there is something going wrong with the powerful laser beam that is at the core of LIGO, TOASTR is supposed to literary spring into action to redirect the beam to a “beam dump” that can absorb the energy circulating in the system which otherwise would probably be sufficient to laser-cut stuff. Nomen est omen.
So what happened? After a TOASTR had failed to actuate on one occasion, it was decided to replace it with a spare. When testing the spare before installing it, the TOASTR under test broke apart unexpectedly, the mishap was even filmed with an iPhone used as an improvised high-speed camera. The problem with this kind of repairs is that they require some of the vacuum systems that are at the heart of LIGO to be vented, and after the repair the system has to be evacuated again which is no trivial task because the vacuum is spectacular in its perfection.
But now the two LIGO observatories are again operational in tandem and together with the VIRGO detector in Italy ready to detect and localize in the sky any Binary Neutron Star Merger event that nature might decide to throw at us. Fingers crossed…