Sun's magnetic building blocks revealed by Sunrise Mission

Fig. 1 This image taken by the instrument IMaX shows the granulation in the Sun’s photosphere. In the bright regions hot plasma wells to the surface; in the dark regions the cooled plasma sinks down again. In between tiny, bright spots can be seen. The individual granules have a size of several thousand kilometres. The bright points measure approximately 100 kilometres in diameter. Image: MPS

 Scientists from the Max Planck Institute for Solar System Research (MPS) in Germany have now for the first time uncovered and characterized the smallest building blocks of the Sun’s magnetic field. In these tiny regions of only a few hundred kilometres in diameter the strength of the magnetic field exceeds the Earth’s magnetic field strength by a factor of approximately 3,000. Researchers from the MPS, the Kiepenheuer-Institut for Solar Physics and further partner institutions analyzed data gathered last year with the help of the solar observatory Sunrise. Until now, no other solar telescope was able to determine the exact properties of these structures. (Physorg)

These and further first results of the Sunrise mission have now been published in twelve articles by the Sunrise team in a special edition of the Astrophysical Journal Letters (vol. 723, pp. L127-L189).

The Sun is a turbulent place. Hot plasma is constantly in motion, wells up from the hot interior of our star, cools and sinks down again. In the photosphere, the visible surface of the Sun, these bubbling flows create net-like structures a few thousand kilometres in diameter. Underneath the bright, hot regions the plasma bubbles to the surface. In the dark, cooler rims it recedes again. Scientists refer to these patterns as granulation.

Since the kinetic energy of these flows of hot plasma can transform into magnetic energy, the currents within the Sun are closely linked to the star’s magnetic properties. One expression of this magnetic nature are the dark sunspots that can even exceed the Earth in size. However, the Sun’s magnetic field also consists of much smaller structures. Tiny, bright points between the granules are an indicator of these fields. Within the bright points strong magnetic fields squeeze the bubbling plasma outward so that it is possible to look deeper within the Sun’s interior. Due to the higher temperatures there, these bright points appear brighter than their surroundings.

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Fig. 2 The bright points in the Sun’s photosphere indicate strong magnetic fields. Top: This image taken by the instrument IMaX shows the intensity of the bright points and their surroundings. Bottom: The corresponding strength of the magnetic field. In both images the size of Germany is included for comparison. Image: MPS

Even though several solar telescopes are able to visualize these bright points, their physical properties such as the magnetic field strength could not be identified until now.

“Without this knowledge one of the most important requirements for a fundamental understanding of the magnetic processes within the Sun was missing”, explains Prof. Dr. Sami K. Solanki, Managing Director of the MPS. “It was like trying to study an anthill without being able to discern and describe the individual ants”.

Only the solar observatory Sunrise built and operated by an international team headed by the MPS unites the crucial properties: a high spatial resolution of about 100 kilometres and precise instrumentation for measuring physical parameters such as the magnetic field. During the observatory’s flight in June of last year, a balloon filled with helium carried Sunrise up to a height of 37 kilometres into the stratosphere. There, Sunrise had left the largest part of Earth’s atmosphere behind — and thus the perturbing influence of air turbulence. With a main mirror of one meter in diameter, the Sunrise telescope is the largest solar telescope ever to have left the Earth. In addition, unlike earthbound telescopes Sunrise was also able to study the Sun’s ultraviolet (UV) radiation that is essentially absorbed by the Earth’s atmosphere and doesn’t reach the ground. 

More information: Sunrise homepage LINK`http`star.mpae.gwdg.de/Sunrise/`color: rgb(14, 50, 102); font-weight: bold; `LINK … .de/Sunrise/