Introduction to LIGO & Gravitational Waves

Sources of Gravitational Waves


3D visualization of gravitational waves produced by 2 orbiting black holes. [Image: Henze, NASA]

3D Visualization of Gravitational Waves Produced by 2 Black Holes
In general, any acceleration that is not spherically or cylindrically symmetric will produce a gravitational wave.  Consider a star that goes supernova.  This explosion will produce gravitational waves if the mass is not ejected in a spherically symmetric way, although the center of mass may be in the same position before and after the explosion.  Another example is a spinning star. A perfectly spherical star will not produce a gravitational wave, but a lumpy star will.

The gravitational waves that modern detectors are sensitive to would be in the audible frequency range if they were sound waves.  In that sense, these detectors can be thought of as ‘gravitational wave radios.’  Just like radio waves cannot be heard without a radio to detect the radio waves and decode the music signal to send to the speakers, gravitational waves cannot be heard without a detector to distinguish the gravitational wave and send that signal to speakers.  All of the physics that went into the production of a gravitational wave is then encoded in this ‘music’ for physicists to decode.  In the following descriptions of gravitational waves, the ‘sound’ they make will often be described to illustrate the properties of the expected signal.  

Listen to an example signal of two neutron stars merging.

Listen to the same signal mixed in with noise. Noise in the LIGO detectors are mostly caused by vibrations from the local environment.

There are four main sources of gravitational waves caused by different kinds of motion and changing distributions of mass - continuous, inspiral, burst, and stochastic.

» Next:  Continuous Gravitational Waves