Inspiral Signal

(A Processing program showing the gravitational wave signal of colliding black holes)

Kat Grover


The applet below plays the gravitational wave signal produced from two black holes spiraling into each other. Set the masses of the black holes using the sliders and then click play to watch and listen. (This will take a moment to load. There will be a pop-up dialog asking you for the permission required for Java to play sound, please answer with 'Allow'.)

This applet has been built with Processing and makes use of the G4P (GUI for Processing) library.

You can't actually hear gravitational waves, they are small stretches and squashes of space (see Stretch And Squash) not vibrations of the air like sound. However the frequency of the gravitational waves from an inspiral like this happen to be at the same frequency as human hearing.

This means it is possible to represent the gravitational wave as a sound wave and a picture of a wave on the screen. The inspiral of compact objects (black holes and neutron stars) produces a distinctive chirp gravitational wave signal like the one you can hear with the applet. If a chirp signal is found in the data from a gravitational wave detector then we known that it must come from such an inspiral. As you can hear, changing the masses of the two black holes causes a small change in the form of the chirp signal. By studying the form of the signal and matching it to models it is possible to discover the physical properties of the source of the waves.

To create these sounds and images an idealized system has been used, allowing us to see the essence of the physics. The simplifications mean point like particles are moving according to Newton's laws. They then emit gravitational waves which cost energy. This loss of energy means the orbit will get smaller, causing a spiral inwards. For more information see Gravitational Waves: Volume 1 Theory and Experiments by Michele Maggiore.