A composite image. Left image of a computer simulation of two black holes surrounded by space and stars. Center image of the Livingston, Louisiana LIGO detector site from above. Right image of the power recycling optic 2 at LIGO.

Exploring Space-Time With LIGO

First opened in 1999, LIGO was the first to detect ripples in space-time.

Have you ever looked up at the night sky and wondered about the mysteries hidden in those distant specks of light?

Turns out, it's a violent universe out there — massive black holes merging, supernovae exploding and neutron stars colliding. And when these events play out, space itself moves.

two converging black holes
The collision of two black holes — an event detected for the first time ever by the Laser Interferometer Gravitational-Wave Observatory, or LIGO — is seen in this still from a computer simulation.

Credit: Simulating eXtreme Spacetimes (SXS) project

From theory to evidence 

Ripples in space-time, known as gravitational waves, were first predicted by Albert Einstein in 1916. But they wouldn't be confirmed until 2015, when the U.S. National Science Foundation's Laser Interferometer Gravitational-Wave Observatory (LIGO) detected the waves created by the collision of black holes 1.3 million light-years from Earth. 

This groundbreaking work earned physicists Rainer Weiss, Barry Barish and Kip Thorne the 2017 Nobel Prize in physics.

Gravitational waves cause space to stretch and squeeze, which can be measured through LIGO's detection beams. The waves are 1,000 times smaller than the diameter of a proton, so the detectors must be extremely sensitive. LIGO's detectors consist of L-shaped vacuum tubes, each 4 kilometers long — just under 2.5 miles.

An interferometer detects the interference between waves (i.e., light, radio or sound). When similar types of waves are in sync, it creates a larger signal that the interferometer can detect. The more out of sync the waves are, the less of the signal is detectable.

To the future and beyond 

Since this first milestone, LIGO's new enhancements have turned the detection of once elusive gravitational waves into a weekly occurrence, opening a new window to the universe. 

The observatory has also detected a mysterious object that could be the heaviest neutron star or the lightest black hole ever discovered, and in 2017, alongside the European Virgo detector, recorded the collision of two neutron stars.

Technician inspects one of LIGOÕs core optics
Before sealing up the chamber and pumping the vacuum system down, an optics technician inspects one of LIGO's core optics (mirrors) by illuminating its surface with light at a glancing angle.

Credit: Matt Heintze/Caltech/MIT/LIGO Lab