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Queen’s scientists unlock another mystery of the Sun

Scientists at Queen’s University Belfast are part of an international research team which has made an exciting new discovery of how magnetic waves can help to heat the Sun.

The Sun is the source of energy that sustains life on Earth but there are still many mysteries around how it works and why its outer layer is over 10 million degrees while its solar surface - the region we see in the sky - is just 6,000. 

For decades researchers have been developing new instruments to capture the dynamics of the plasma – the gas which makes up the solar atmosphere. They have been able to show that magnetic fields play an important role in transporting energy to the corona but questions remain around how this happens.

Now, an international team involving a scientist from the School of Mathematics and Physics at Queen’s University Belfast has shed further light on the problem through the discovery of elusive Alfvén waves, in an Earth-sized magnetic pore in the solar photosphere.

The team, led by Dr Marco Stangalini from the Italian Space Agency, included Dr Chris Nelson, a Post-Doctoral Research Fellow from the Astrophysics Research Centre at Queen’s. The experts used state-of-the-art observations and numerical simulations to track the rotation of the magnetic field itself in the pore and identify Alfvén waves as the driver.

Originally theorised in 1947 and named after their discoverer Professor Hannes Alfvén, signatures of these purely magnetic waves have been widely sought by solar physicists due to their ability to transport energy and information over very large distances, especially across large temperature and density gradients which act as walls to other ‘acoustic’ waves.

Dr Chris Nelson from Queen’s explains the key findings: “Our research team was able to confirm for the first time the existence of direct signatures of rotational Alfvén waves in a solar pore by tracking the motion of the magnetic field itself. We were also able to identify anti-symmetric components, where the magnetic field in different parts of the flux tube rotates in different directions, which may prove to be pivotal in the removal of vast amounts of energy from the solar photosphere into the corona.”

The research brought together a range of different and complementary expertise. Dr Nelson’s expertise in the analysis of complex multi-dimensional datasets and signal analysis was crucial in obtaining results from the state-of-the-art observational data.

In addition to these observations, supporting numerical simulations were carried out by researchers from Queen Mary University of London to provide new insights into how these peculiar and important magnetic waves are formed in the Sun. The experts found that these waves should form across a range of structures in the solar atmosphere as a natural response to certain movements in the solar photosphere and the results of this study have been published in Nature Astronomy.

Commenting on the research, Dr Nelson said: “The detection of torsional oscillations in the visible imprints of the magnetic field itself is a wonderful result. The research environment and training received from Queen’s has allowed me to contribute to this project in a meaningful and extensive way, and will allow me to develop my career further in the future. This work opens up a range of future researches that can really test our understanding of how frequent and important Alfvén waves are in the solar atmosphere. I look forward to making further progress over the next few years.”

Professor Mathioudakis, who is the Head of Astrophysics Research at Queen’s, said: “The generation, transport and dissipation of energy in the solar atmosphere is one of the most challenging problems of modern physics. This discovery of magnetic waves in the photosphere of a solar pore makes a vital contribution for its solution.”

The direct discovery of these waves in the solar photosphere, at the top of the energy reservoir of the Sun, is just the first step towards finally understanding and exploiting the capabilities of these magnetic waves.

There will soon be many more opportunities to research the relevance of Alfvén waves, through unprecedented opportunities offered by the next generation of instruments such as the Solar Orbiter satellite, the 4-m aperture ground-based Daniel K. Inouye Solar Telescope (DKIST), and the future European Solar Telescope (EST).

DKIST will begin collecting science data this year, with Queen’s University leading the UK involvement through the development of brand-new detector technology.