Hi, I’m Marley, the astronomer here at the Space Centre. This month we are taking a look at some spooky things in space. The one thing that people always mention to me as being scary is the sound of a pretty terrifying object: a black hole.
In 2022, NASA revisited data collected from the black hole at the centre of the Perseus galaxy cluster. Sound waves that astronomers previously detected in 2003 were made audible for the first time. You can take a listen here. But how did scientists get noise from a black hole, when sound does not exist in space?
To start, sound waves need to have a medium to travel through. Since most of space is a vacuum, it is true that in most of space, there is no medium for sound waves to travel through. But when you are in a galaxy cluster like the Perseus galaxy cluster, there is a lot of gas for sound waves to pass through. In the case of the Perseus galaxy cluster, pressure waves coming from the black hole causes ripples in the gas. These ripples could be translated into notes, but not any that humans could hear. Scientists scaled the soundwave signals 57 to 58 octaves above their actual pitch so that we could hear them. The process of translating data into sound is called sonification, and it is becoming more popular as a way to share astronomical data. Think of it as though the scientists are acting like cosmic DJ’s! They are remixing the sound wave signals to give us a soundtrack of the universe.
All sonification involves taking observational data from telescopes and translating it into frequencies that can be heard by the human ear. However, the techniques used will change based on the object, the data available, and what scientists are trying to express. There is the example above, where actual sounds were pitched up so that we can hear them, but this example of the Milky Way works completely differently. Here, the sounds represent position and brightness of sources. Instead of looking at the image and noticing the position and brightness of stars, you hear them instead.
Data sonification is gaining in popularity, but it is not new. A famous sonification example is the sound of two black holes colliding, or the ‘chirp’ from the first gravitational wave detection from LIGO. The first sustained sonification program was started by experts at the Chandra X-Ray Center and System Sounds as a way to reconnect members of the blind and low vision community with astronomical data. In 2020, the COVID-19 pandemic impacted the 3D modeling/printing projects going on at the time, and a new way was needed to share astronomical data. What started off as a tool for outreach has now expanded into an entirely new way for scientists to understand their data.
Check out the activities below to learn more about data sonification, and other sounds we hear in space!
Sounds of the Milky Way
In the example I provided of the Milky Way, the data are from the x-ray, optical, and infrared parts of the electromagnetic spectrum. Here you have the opportunity to listen to them all separately.
Ask yourself: Why might scientists combine data? Why might they want to leave it separate?
Sagittarius A* (EHT Image)
Here, you can listen to the black hole at the centre of our galaxy. In this example of sonification, changes of volume and higher frequencies of sound both represent aspects of the image.
Compare it to this sonification of the galactic centre of the Milky Way.
Ask yourself: What is each sonification trying to express?
Sounds on Mars
Data sonification is representing data as a sound, but did you know we have actually heard sounds on another planet?
On Mars, the Perseverance rover is carrying two microphones, which has let scientists to record the sounds of Mars directly for the very first time. With a very different atmosphere than we have on Earth, the sounds on Mars are very different. Check out the sounds of Mars here.
Ask yourself: What planet would you like to hear the sounds from? What do you think they would sound like?