Star's song captured by scientists
Published 08/11/2010 | 09:57
Scientists have captured the 'song' of a distant star as part of new research that is providing insights into what lies beneath its surface.
Astrophysicists from the University of Birmingham and scientists working with Nasa have measured the changes in the brightness of light coming from the star KIC 11026764, which has been nicknamed Gemma and is about twice the size of the sun.
They found the star, which is 3,100 trillion miles away from the Earth, vibrates rather like a musical instrument due to so called "starquakes" that resonate from the surface to the core.
Using a technique called astroseismology they were able to detect the flickers of light caused by these starquakes and reconstruct the sound produced by the star.
The harmonic hum, which sounds a little like wind blowing over a microphone, has revealed new information about the internal structure of the star, explained Dr Bill Chaplin, an asteroseismologist at Birmingham University who took part in the research.
He said these vibrations could help astronomers learn more about the age, size and composition of other stars.
He said: "Essentially stars resonate like a huge musical instrument. Stars make sounds naturally but we can't hear this as it is has to travel through space.
"Like a musical instrument, stars are not uniformly solid all the way to their core, so the sound gets trapped inside the outer layers and oscillates around inside.
"This makes the star vibrate causing it to expand and contract. We can detect this visually because the star gets brighter and dimmer and so we can reconstruct the sounds produced from these vibrations."
The new research comes just six months after scientists at Sheffield University recorded eerie musical harmonies emitted from the surface of the sun.
Dr Chaplin worked with an international team of scientists using data captured by Nasa's Kepler space telescope, which is searching for planets orbiting stars in our galaxy.
The Kepler spacecraft searchers for tiny fluctuations in the light coming from thousands of stars in its field of view in the hope of detecting small dips in brightness caused by planets orbiting around them.
The scientists found that they could also use the telescope to pick up other changes in brightness caused by starquakes.
In the same way as a cello produces a deeper note than a violin, the larger a star is the lower the frequency at which it vibrates, allowing scientists to calculate the size of a star.
They can also determine information about what the star is made of and what its internal structure may be from the way the sound waves move through the star – sound waves pass through dense helium cores more quickly than through hydrogen, changing the tone heard at the surface. The vibrations then affect the light given off by the star.
Using their measurements they calculated that Gemma is more than 5.94 billion years old, around a billion years older than our own sun.
It has grown to be twice the size of the sun and will continue to grow as it transforms into a red giant, which are massive stars that are coming to the end of their life.
The scientists also found that Gemma has a core made up predominantly of helium which is surrounded by a thin shell where the hydrogen fusion reaction that powers the star takes place.
"We are just about to enter a new area in stellar astrophysics," said Thomas Kallinger, lead author on a study of red giant stars and postdoctoral fellow at the Universities of British Columbia and Vienna.
"Kepler provides us with data of such good quality that they will change our view of how stars work in detail."