Professor Bill Chaplin (University of Birmingham) interview: hertz Unlimited project – The songs of our stars

hertz is an innovative research and development project, and the creation of experienced Lead Artist Juliet Robson. It is supported by arts commissioning programme Unlimited, which celebrates the work of disabled artists, with funding from Arts Council England. hertz diversely marries four fields of study: art, astrophysics, mathematics and meteorology. The project aims to allow audiences to discover what noise, trapped inside stars in space, sounds like – and what it looks like in the shape of patterns it creates. Further, hertz aims to translate infrasound, which we cannot hear, into physical sensations people can experience.

Professor Bill Chaplin – of the School of Physics and Astronomy at the University of Birmingham – is collaborating on the project. Here, he describes what drew him to hertz and explains how stars create sound in the first place, and what we can learn from it

Professor Chaplin, why did you first become involved in hertz?

It was through being contacted by Lead Artist Juliet Robson. I was very interested and intrigued by what she had to say. Personally, I have a long-standing interest in collaborations between artists and scientists, which is manifested in collaborations I have had with other artists previously.

I am interested in how artists and scientists can interact professionally and how they can influence each other’s practice. I am particularly interested in hertz in how it might change my views on how I work and how I might articulate that in the future. For example, I might be talking to my wife one evening and she will often preface a question with, ‘Forgive my ignorance, but…’ It usually isn’t ignorance. They are usually questions which make you question your own assumptions on an issue.

What do you hope to achieve through hertz?

Like I have said, I am very keen to see how Juliet and I can influence each other’s practice through collaboration. Also, I am interested to discover new ways to use the astronomical data we have and collect to engage with the public – making it accessible to people who otherwise might not be engaged with science. hertz, I think, is certainly going to provide another way to do that and in a very innovative way. I guess people will come to see and experience hertz for the art, but if members of that audience come away from seeing the work and say, ‘Hey, stars resonate like musical instruments’, that will represent real success.

Sine wave:189-191hz
Star Kepler-36/260hz
Star Kepler-36/190hz


Sound of Kepler-36 a sun star found in the Cygnus constellation which can currently be seen in the northern hemisphere.


Cross section of a sun star, showing an orange section just below the spherical surface.
Cross section of a sun star: sound made by turbulent gas occurs in the orange section.

Professor, describe your background.

I am an astronomer. I study stars and also search for planets orbiting other stars in our galaxy. The technique we use to do that is through natural resonances produced by stars, which make sound within their interiors and which resonate like great, big musical instruments. Because stars are big balls of gas – they are not solid objects – that trapped sound makes stars gently breathe in and out. By measuring that breathing we can learn what stars look like inside and, importantly, it is the only way we can do that. It allows us very accurately to calculate how big stars are and how old they are. That is particularly important when we discover a star surrounded by planets, because we only know the planets as well as we know the star which they orbit.

That is the research I do at the University of Birmingham and have been doing in my career for more than 20 years. The fact that stars resonate was first discovered here in the 1970s at the university when we learnt that our sun breathes in and out – which is why I am based here and doing the work that I do in Birmingham.

However, we had to wait until the 1990s to be able to detect these very gentle oscillations in other sun-like stars, through the advent of new satellites and big telescopes like the NASA Kepler Mission, which we use and is making our ability to study stars in detail a reality.

The Kepler Mission; large telescope in space

What first inspired you to become an astronomer?

It would have been following and being intrigued by the NASA space programme as a kid. If I had followed that interest through logically, I would have become an engineer, but I didn’t – I got sidetracked by the science and completed my PhD in building instrumentation that could enable us to detect clouds around other stars and also measure this oscillation in stars. I then started studying the sun and other stars for the next 10 years until around 2005. Then we realized things were about to happen with how we study stars through new technology. The data we can now glean from other stars helps us understand our own sun. For many years that understanding was only one-way. The sun was like a Rosetta Stone for astronomers, helping them understand other stars.

Kepler-68, solar type star hosting three planets; frequency spectrum with peaks at around 2100 micro hertz.
Why do stars create sound?

A star like our sun makes sound because its outer layers are turbulent through a process called convection, which can be created simply in an oven or by a pan of hot water on a stove. Convection involves parcels of gas moving around and circulating, and as they do that and buffet one another, turbulence happens which produces changes in pressure and sound waves. Even though a star like the sun does not have a solid edge, it does act as a natural cavity to trap that sound and creates resonances like in the body of a musical instrument. Because the sun is a big ball of gas, the compressions and relaxations of the trapped sound waves make the star breathe in and out.

It might sound a stretch to talk glibly about ‘the music of the stars’. ‘Really?’ But the answer is yes, stars really make sound. A star like our sun produces oscillations which are very tiny but which are very rich and create many harmonics we can observe. Other types of stars called Cepheids, which are much bigger than our sun have a different structure and produce huge pulsations in this way, which can change their brightness by as much as 20 per cent. You can actually observe those changes yourself with the naked eye through a telescope, but if you looked at the sun, no chance, the oscillations are too small.

How far away are the stars being used for hertz?

Some of the stars we are going to look at in hertz have first been observed by the NASA Kepler Mission and are more than 100 light years from Earth. Light would take more than 100 years to travel from them here to Earth.

What do you hope audience members will gain from seeing hertz?

A greater appreciation that stars do make sound.

Finally, is there life on other planets?

Yes, I think there is. My personal view is that it would be a very strange universe if we were the only life within it. Whether we discover definitive evidence within our lifetimes, remains to be seen, but, no, I don’t think we are alone.