At the end of August 2018, the Advanced LIGO and Advanced Virgo detectors finished their second observation run. As well as further binary black hole mergers, for the first time, a binary neutron star merger was observed. This event was immediately associated with a short gamma ray burst, and with subsequent observations across the electromagnetic spectrum, opened up the field of multi-messenger.

In this colloquium, I will provide an overview of the two observation runs, and discuss the implications of the current detections for alternative theories of gravity and neutron star equation-of-state models.

APC