About 1.3 billion years ago, two black holes came into catastrophic collision with one another at half the speed of light morphing into a singular black hole.

100 years ago, Einstein predicted that massive objects would create gravitational waves, but was skeptical that any measurement could be observed.

On September 14^th, 2015, scientists at LIGO (Laser Interferometer Gravitational-Wave Observatory) heard a chirp.

Last Thursday, those same scientists at LIGO announced that, yes, Einstein was right. The chirp was the sound of the gravitational waves produced by those black holes.

Under Einstein’s theory of relativity, the concept of time and three dimensional space are interwoven into a fourth dimensional fabric. To best understand this, imagine spacetime as a trampoline, then imagine a massive stellar object like a black hole as a bowling ball on the trampoline, and having other objects roll towards it. Time and space are warped from the mass of the black hole by its gravitational force. When, for example, another black hole is drawn in by the gravitational force of another they collide, sending gravitational waves that ripple through the curvature of spacetime.

These gravitational waves have extremely violent and powerful origins, but once they travel through interstellar space to reach us here on Earth the waves are, luckily for us, much smaller--millions of times smaller (check out Neil deGrasse Tyson’s video below of what happens if you get too close to a blackhole).

The gravitational waves that LIGO detected are so weak the amount of spacetime movement they generate is one thousand times smaller than an atomic nucleus. So how do scientists detect such miniscule gravitational waves? They use an interferometer.

An interferometer is a tool of investigation that combines two or more sources of light to create a measurable interference point. Interferometers are used because of their ability to make microscopic measurements. Two interferometers were used to capture the sound of the merging black holes, one in Washington state and the other in Louisiana. The interferometers used at LIGO are 2.5-mile-long tubes placed perpendicular to each other in an L-shape. Inside these tubes are laser beams reflecting off of mirrors placed at the intersection and ends of the tubes. When gravitational waves hit earth they distort the length of the tubes causing a misalignment of the laser beams inside the tubes that can then be measured and analyzed.

Gravitational waves that are detected are then translated into sound waves which are in the audible range for humans, creating what we hear as the chirp!

What is most exciting about this discovery is the new understanding of the universe. Gravitational-wave astronomy is unique because before all we knew of the universe came from astronomy made observations with telescopes and light particles. Observing the universe exclusively through light becomes challenging because light can be distorted through matter; gravitational waves, however, travel unobstructed through the very fabric of the universe.

Another possibility open to scientists is being able to explore the beginning stages of the universe. Only observing the universe through light gets tricky once scientists want to look at the beginnings of the universe because space was so dense and hot during the big bang that light was very opaque. Since gravitational waves can pass through the universe unhindered, scientists can observe these early gravitational waves so get an otherwise invisible look at the beginnings of the universe.

LIGO has made a fantastic discovery for the world of astronomy; where scientists only had the ability to see, they can now hear.

Check out the audio clip below to hear the galactic chirps.