Gravitational Waves

What are Gravitational Waves?

Gravitational waves are distortions or 'ripples' in the fabric of space-time caused by some of the most violent and energetic processes in the Universe. Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity. Einstein's mathematics showed that massive accelerating objects (such as neutron stars or black holes orbiting each other) would disrupt space-time in such a way that 'waves' of distorted space would radiate from the source. Furthermore, these ripples would travel at the speed of light through the Universe, carrying with them information about their cataclysmic origins, as well as invaluable clues to the nature of gravity itself.


The strongest gravitational waves are produced by catastrophic events such as colliding black holes, the collapse of stellar cores (supernovae), coalescing neutron stars or white dwarf stars, the slightly wobbly rotation of neutron stars that are not perfect spheres, and the remnants of gravitational radiation created by the birth of the Universe itself.

Though gravitational waves were predicted to exist in 1916, actual proof of their existence wouldn't arrive until 1974, 20 years after Einstein's death. In that year, two astronomers working at the Arecibo Radio Observatory in Puerto Rico discovered a binary pulsar--two extremely dense and heavy stars in orbit around each other. This was exactly the type of system that, according to general relativity, should radiate gravitational waves. Knowing that this discovery could be used to finally test Einstein's audacious prediction, astronomers began measuring how the period of the stars' orbits changed over time. After eight years of observations, it was determined that the stars were getting closer to each other at precisely the rate predicted by general relativity. This system has now been monitored for over 40 years and the observed changes in the orbit agree so well with general relativity, there is no doubt that it is emitting gravitational waves.

Why Detect Them?

The gravitational waves that are detectible by LIGO will be caused by some of the most energetic events in the Universe—colliding black holes, exploding stars, and even the birth of the Universe itself. Detecting and analyzing the information carried by gravitational waves will allow us to observe the Universe in a way never before possible. This will open up a new window of study on the Universe, giving us a deeper understanding of these cataclysmic events, and usher in brand new cutting-edge studies in physics, astronomy, and astrophysics.

Historically, scientists have relied primarily on observations with electromagnetic radiation (visible light, x-rays, radio waves, microwaves, etc.) to learn about and understand objects and phenomena in the Universe. (In recent years, subatomic particles called neutrinos have also been used to study aspects of the heavens.) Each of these sources of information provides scientists with a different and complementary view of the Universe, with exciting new discoveries occurring as each new 'window' has been discovered, introduced, and utilized.

Gravitational waves are not electromagnetic radiation. They are a completely different phenomena, carrying information about cosmic objects and events that is not carried by electromagnetic radiation. Colliding black holes, for example, emit little or no electromagnetic radiation, but the gravitational waves they emit will cause them to "shine brightly" like beacons on an utterly dark cosmic sea. More importantly, since gravitational waves don't interact with matter (unlike electromagnetic radiation), they travel through the Universe completely unimpeded giving us a crystal clear view of the gravitational-wave Universe. They will carry information about their origins that is free of the distortion or alteration suffered by electromagnetic radiation as it travels through millions of light years of intergalactic space. With this completely new way of examining astrophysical objects and phenomena, gravitational waves will truly open a new window on the Universe, providing astronomers and other scientists with their first glimpses of previously unseen and unseeable wonders, and greatly adding to our understanding of the nature of space and time itself.