They may look like diamonds in the sky, but what do twinkling stars sound like? Astronomers have developed a new way to understand what causes starlight to flicker – and you can listen to it.
Rather than the visible twinkling we can see from Earth, which is caused by our planet’s atmosphere, this song reveals the flickering caused by movements within stars’ cores.
The findings, published in the journal Nature Astronomy, may help us learn more about what’s happening inside massive stars (stars that over 1.2 times larger than our Sun). This includes how stars and galaxies form and evolve, as well as how the elements we depend on – like oxygen – are created.
The twinkling of large stars is caused by gas waves rippling on their surfaces. Gas waves originate in the nuclear reactors sitting in the centres of massive stars.
These places, known as ‘convection zones’, are turbulent and chaotic as gases collide and push heat outwards. These processes produce waves which cause starlight to alternately brighten and fade, producing the twinkling effect.
The team of scientists at Northwestern University in the US turned these waves into audio waves to create the sound of twinkling stars.
“This study provides an out of the box method to search for stars’ signatures that are largely masked and are invisible even to more powerful telescopes and to the human eye,” sonification astronomer Wanda Díaz-Merced, who was not involved in the study, told BBC Science Focus. “I congratulate the team!”
So how did they do it? They started by creating the first ever 3D simulations of the energy that ripples from a massive star’s core to its outer surface. These simulations revealed how astronomers expect twinkling waves to appear if viewed through a powerful telescope.
“Motions in the cores of stars launch waves like those on the ocean,” said Northwestern’s Evan Anders, who led the study. “When the waves arrive at the star’s surface, they make it twinkle in a way that astronomers may be able to observe.”
Anders and his team then developed these simulations into computer models, and then used these models to calculate how much twinkling is caused by different frequencies and intensities of the waves.
They converted these calculations into an audio track to illustrate the movement of the waves.
The resulting track, however, is a human ‘translation’ of the song. Because the twinkling waves are outside the range of human hearing, the researchers increased the frequencies of the waves to make them audible.
A musical form allowed the scientists to combine two processes that operate on very different timescales. The initial turbulence of the gases colliding which takes a matter of weeks, and the waves themselves which reverberate for hundreds of thousands of years.
Their inspiration came from the idea that musical sounds are initially generated by an instrument, but then the sound waves they produce reverberate around a room.
When made into an audio track, the sound shifts from a clear sound to something more eery, which represents the movement of the waves from the core out to the surface.
The team reversed the simulation to demonstrate the effect the other way – feeding ‘human’ songs into the computer model to see what would happen to the sound waves if passed through the core of a star and outwards.
Their aptly chosen songs – Twinkle Twinkle Little Star and orchestral suite The Planets by composer Gustav Holst – became beautiful and haunting in the process.
“Stars get a little brighter or a little dimmer depending on various things happening dynamically inside the star,” Anders said.
“The twinkling that these waves cause is extremely subtle, and our eyes are not sensitive enough to see it. But powerful future telescopes may be able to detect it.”
The work will help to direct these future telescopes to the inner regions of stars where heavier elements are forged.
This may help to explain a yet unresolved mystery. While the convection waves partially explain the stars’ flickering, they are not travelling at the frequencies or intensities to match the astronomers’ observations. The simulations developed by the Northwestern scientists is a big step – but we still have a lot to learn about what is going on deep inside massive stars.
About our expert:
Wanda Díaz-Merced is the leading expert in the sonification of astrophysical data. She completed her PhD in computer science at the University of Glasgow and has completed research at the NASA Spaceflight Centre. Her research has been published in the journal Monthly Notices of the Royal Astronomical Society and Proceedings of the International Astronomical Union.
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