On August 17, 2017, the US LIGO and European Virgo gravitational wave detectors made a monumental discovery, of the inspiral and coalescence of a pair of neutron stars. The collision of neutron stars created massive fireworks that is still visible to the best telescopes. Two seconds after LIGO's discovery, Fermi Gamma-ray Space Telescope and the International Gamma-Ray Astrophysics Laboratory, both observed short gamma-ray bursts from the same source. LIGOVirgo detection triggered an observational campaign by some 70 telescopes all over the world, leading to the identification of the host galaxy, followed by detection of the counterpart in infrared, UV, X-rays and radio in the following hours and weeks. These observations are already pro viding us with clues to some of the long-standing problems in astrophysics while raising new ones that require a closer examination of merger events. In this talk, I will describe gravitational waves, how LIGO made the discovery, what we have learned from LIGO’s discoveries so far and what we can expect to learn in the future. It is particularly exciting to come back to an institution some 40 years later where a similar talk helped me choose between engineering and physics.
