In 2015, humanity heard the cosmos for the first time. Not seen, but heard: through the faint ripples in spacetime caused by the merger of two black holes 1.3 billion light-years away. These were gravitational waves – predicted by Einstein in 1916 but thought elusive.
The discovery was made by the Laser Interferometer Gravitational-Wave Observatory (LIGO) project. Two giant detectors in the United States, each with 4-kilometer-long arms, measured changes in wavelength smaller than one-thousandth the diameter of a proton. It’s like measuring the distance to the nearest star with an accuracy of a hair’s breadth.
As the black holes (with masses of 29 and 36 suns) began orbiting each other, they emitted energy in the form of gravitational waves. In the final fraction of a second, they merged, creating a ripple that reached Earth on September 14, 2015, at 09:51 UTC. The signal lasted 0.2 seconds, but it changed astronomy forever.
Until then, we studied the universe only through electromagnetic radiation: light, radio waves, and X-rays. Gravitational waves are a new sensation. It’s as if someone who’s been blind all their life suddenly sees the world. We can now “hear” events invisible to telescopes: neutron star mergers, the birth of black holes, even possible traces of the Big Bang.
In 2017, LIGO and the European Virgo detector detected the collision of two neutron stars. 1.7 seconds later, the Fermi space telescope detected a gamma-ray burst. This was the first multi-channel observation, and it confirmed that heavy elements (gold, platinum) are born precisely in such collisions.
