Ten years ago, we heard the universe whisper for the first time. On September 14, 2015, the Laser Interferometer Gravitational wave Observatory (LIGO) detected ripples in space-time. The signal came from the gravitational waves that had traveled 1.3 billion years to reach Earth, carrying the story of two colliding black holes. This historic moment, predicted by Einstein a century earlier, opened an entirely new way of experiencing the universe.
Today, LIGO has transformed from making a single groundbreaking detection to becoming a discovery machine, routinely spotting black hole collisions roughly every three days. The evolution of LIGO's capabilities has been remarkable. Working alongside international partners Virgo in Italy and KAGRA in Japan, the gravitational wave network has now captured approximately 300 black hole mergers. During their current science run, they've discovered more than 200 candidate black hole mergers which is more than double the number found in their first three runs combined.
This dramatic increase stems from continuous technological improvements that have made LIGO extraordinarily sensitive. The detectors can now measure space-time distortions smaller than 1/10,000th the width of a proton, that’s 700 trillion times smaller than a human hair. These are the most precise measuring instruments humans have ever created.
"Just 10 short years ago, LIGO opened our eyes for the first time to gravitational waves and changed the way humanity sees the cosmos. There's a whole universe to explore through this completely new lens,” - Aamir Ali from the National Science Foundation.
LIGO's improved sensitivity is perfectly demonstrated by the recent gravitational wave discovery GW250114, detected on January 14, 2025. While similar to LIGO's first detection which both involved black holes about 1.3 billion light-years away, this new signal is dramatically clearer thanks to a decade of technological advances.
The detection allowed scientists to perform the most precise test yet of Stephen Hawking's black hole area theorem, which states that the total surface area of black holes cannot decrease. By analysing the gravitational waves, researchers could "hear" the black holes growing as they merged. The initial black holes had a combined surface area roughly the size of Oregon, while the final merged black hole was about the size of the US state of California, not the small town on the coast of the UK!
LIGO is achieving so much more. In August 2017, it, and Virgo witnessed a collision between two neutron stars, known as a kilonova that hurled gold and other heavy elements into space. This event marked the birth of so called "multi-messenger astronomy," as dozens of telescopes around the world simultaneously observed the same event in both gravitational waves and light.
The recent success of LIGO required inventing entirely new technologies, many of which now benefit other fields. Innovations include ultra-stable laser system platforms, near perfect mirror coatings, and "quantum squeezing" techniques that push beyond the normal limits of quantum physics.
Looking ahead, scientists are planning even more ambitious projects. LIGO India will join the global network, while the proposed Cosmic Explorer which has arms 40 kilometres long compared to LIGO's 4 kilometre arms, could detect the universe's earliest black hole mergers.
Source : Ten Years Later, LIGO is a Black-Hole Hunting Machine