Wave Physics with LIGO data

Learn about sources from their signals

Sources and signals

Key ideas:

  • Sources with high frequency motion prouduce high frequency signals
  • Musical instruments display the connection between signal frequency and source properties
  • In astronomy, we learn about the sources (stars and black holes!) by studying their signals (light and gravitational waves!)

Sound Waves

Lower pitch sounds have longer wavelengths. Musical instruments are designed to resonate with the pitches they produce, meaning that music from an instrument has wavelengths that match the length of the instrument. This is why larger instruments have lower sounds. You can often hear something similar in animals: larger animals tend to make lower pitch sounds.

Low Frequency

Long Wavelength

High Frequency

Short Wavelength

Low Frequency

High Frequency

Long wavelength sound: large source

Short wavelength sound: small source

Long wavelegnth sound: large source

Short wavelength sound: small source

Low Pitch

High Pitch

Long wavelength sound: large source

Short wavelength sound: small source


The colors we see in visible light correspond to different frequencies of electromagentic waves. Rainbows sort light from the lowest frequency we can see (red) to the highest frequencies we can see (blue or violet).

Light from "thermal radiation" reveals the temerature of the source. The frequency of the light tells us about the motion of the electrons in the source: the hotter the source, the faster the electrons are moving, and so the higher the frequency of light that's emitted.

Low Frequency: Red Light

High Frequency: Blue Light

Cooler stars make red light

Hotter stars make blue Light

Gravitational Waves

Gravitational-wave detectors like LIGO and Virgo can record signals from mergers of black holes. The frequency of the gravitational-wave signal corresponds to the frequency of the black hole orbit, just before merger. In their final moments, larger black holes orbit at lower frequencies, and smaller black holes orbit at higher frequencies. Because of this, we can measure the mass of black holes by the frequencies of their gravitational-wave signals.

By playing a graviational-wave signal through a speaker, we can even hear it - so that just like instruments, a higher pitch tells us to expect a smaller source!

Larger black holes
merge at lower frequencies

Longer wavelength

Lower Frequency

Smaller black holes
merge at higher frequencies

Shorter wavelength

Higher frequency

Got the idea?

Try it!

Contact: gwosc@igwn.org

Image / Audio sources