Since the first generation of telescopes, 400 years ago, astronomers have been paying close attention to the Sun, which can be observed in a level of detail not possible with any other star. But the Sun is much more than a seemingly simple sphere of plasma; the exact structure within is incredibly complex and dynamic. European researchers are using new techniques to investigate the processes taking place inside the Sun.
Data for an ongoing European project is being collected at the Teide observatory on the Spanish island of Tenerife. The tools of this observatory include the Gregor telescope, with huge mirrors for high-resolution images, and the VTT telescope, which uses spectrography to analyse the incoming light rays. But relatively new methods are also being used to receive information about the inside of the Sun.
The structure of the Sun is made up of various layers, rather like an onion. Core fusion takes place at the centre of the Sun, transforming hydrogen into helium and providing the Sun with its energy. A major difficulty in solar physics is not being able to “see” beyond the outer surface of the Sun.
Oskar von der Lühe is director of the Kiepenheuer-Institut für Sonnenphysik in Freiburg, Germany, and is the coordinator of the Helas project. This research project focusses on understanding the inner workings of the Sun. The project applies a branch of science known as helioseismology, in which pressure wave movements on the Sun's surface are measured.
The Helas scientists have been using the GONG project telescope at the Teide observatory in order to measure movements and vibrations of the Sun as a whole. Pulsations at the surface moving as slowly as a few centimetres per second can be detected with this telescope.
Markus Roth, of the Kiepenheuer-Institut für Sonnenphysik, has been analysing these pulsations, which are pressure waves. Since pressure waves can be interpreted as sound waves, the measurements of the Sun can be translated into a frequency range that can be heard by humans. Every star has its own unique sound, depending on internal structure and age. Measurements taken from a white dwarf, a red giant or our Sun sound therefore all different to each other. In this way, the scientists can “hear” the complicated structure of layers and zones.
With particular help from Pere Pallé, a Helioseismologist of the Instituto de Astrofísica de Canarias, much knowledge has already been gained regarding the inner structure of the Sun. For example, how the inside of the Sun rotates: rotating with varying speeds depending on the depth within the Sun. This difference in the rotating of the layers is known as the solar dynamo. It is believed that the solar dynamo is the source of the magnetic cycle of the Sun - explaining the periodical appearance of sunspots. As part of the Helas project the scientists are investigated specific areas within the Sun to measure their influence on the magnetic cycle.
Knowing how the magnetic cycle works and evolves will be a major step in understanding the effects the Sun has on the Earth, the Earth's climate and of course those living there.