Gravitational wave astronomy: observing the dark side of the Universe

Two decades ago the construction of kilometer-scale gravitational wave detectors had started and the sensitivity has continuously been improved. Now these instruments are being upgraded to the second generation, which in a few years’ time will allow the first direct detection of gravitational waves and analysis of some astrophysical processes with gravitational waves. Routine gravitational wave astronomy though, will require the supreme sensitivity of third generation instruments, like the Einstein Telescope, an underground gravitational wave observatory, designed in a pan-European effort.