Sunrise reveals sun's magnetic building blocks

Scientists from the Max Planck Institute for Solar System Research (MPS) in Germany have now for the first time uncovered and characterised 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. 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 (see Figure 1). 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.