Astrophysicists from ELTE also took part in the 15-year international research work in which, by observing the periodically flashing pulses of massive stars, they noticed that gravitational waves stretch and compress space and time following a characteristic pattern. During the research, they monitored the Universe with giant radio telescopes, so that light can be shed on the operation of huge black holes colliding in the middle of distant galaxies, and they can even discover several sources of low-frequency gravitational waves.