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An international team of astronomers, including Saskia Hekker of the University of Amsterdam (UvA), has discovered waves in a star that reach all the way to the core of the star.

Illustration of waves in a star or 'star vibrations' Copyright: Pieter Degroote, K.U. Leuven, Belgium

An international team of astronomers, including Saskia Hekker of the University of Amsterdam (UvA), has discovered waves in a star that reach all the way to the core of the star. The discovery was made thanks to precise measurements with the Kepler space telescope. The research results were published on 17 March in the online edition of the 'Science Express'.

Astronomers already knew that there were waves which pass through stars, like sound waves on earth, but until now waves could only be observed in the outer layers of a star. These waves reach several hundred thousand kilometers deep, until they are reflected at a certain point because the material of the star is so dense that the waves cannot penetrate it. Now, the team unexpectedly observed waves that reach the centre of the star. It is these type of waves (stellar pulsations) that are studied within the field of asteroseismology. Asteroseismology uses star vibrations to form a detailed picture of the interiors of stars.

Red Giants

The special waves were discovered in a red giant. Red giants are stars have come to the end of their life. Our own sun will reach that stage in approximately five billion years. By that time the Sun will be 10 times larger than it is at present, and about 50 times as bright. At the same time the colour will shift from a yellow hue to a red hue, hence the name red giant.

Accurate measurements

‘This discovery will tell us how stars age internally, and therefore what will happens to our sun in the future,’ said Hekker, a postdoc at the Astronomical Institute Anton Pannekoek of the UvA. Hekker is one of many young researchers who have been given the chance to work with data from NASA's Kepler space mission. She was the driving force behind the team of researchers that analysed data on red giants. The vibrations (oscillations) manifest themselves on the surface of the star as sites where the temperature varies slightly in a more or less fixed period. This causes slight variations in the total brightness of the star, and these variations can now be accurately measured with the Kepler telescope. Co-author Joris de Ridder of the University of Leuven, explains: ‘The instrument must be extremely sensitive to see such waves against a background of noise. It must also be long enough to watch these oscillations. Such a star does not vibrate with just one frequency, but with different frequencies simultaneously, which are very close to each other. To be able to differentiate the frequencies of these waves from each other, they must be observed for an extended period of time. Thanks to Kepler, we can meet both these conditions.’

The team is part of KASC, the Kepler Asteroseismic Science Consortium, which comprises more than 440 astronomers who specialise in exploring the interior of stars.

Publication details

P. G. Beck, T. R. Bedding, B. Mosser, D. Stello, R. A. Garcia, T. Kallinger, S. Hekker, Y. Elsworth, S. Frandsen, F. Carrier, J. De Ridder, C. Aerts, T. R. White, D. Huber, M.A. Dupret, J. Montalbán, A. Miglio, A. Noels, W. J. Chaplin, H. Kjeldsen, J. Christensen-Dalsgaard, R. L. Gilliland, T. M. Brown, S. D. Kawaler, S. Mathur, and J. M. Jenkins: ‘Kepler-Detected Gravity-Mode Period Spacings in a Red Giant Star’, in: Science Express, 17 March 2011.