Disentangling magnetic fields in stars

The Max Planck Society awards Dr. Rakesh Kumar Yadav with the Otto-Hahn-Medal for his work on the magnetic fields of stars

June 15, 2016

Dr. Rakesh Kumar Yadav, currently engaged at the Harvard Smithsonian Center for Astrophysics in the USA, receives the Otto Hahn Medal for outstanding young scientists. With this prize the Max Planck Society awards young scientists for their excellent scientific achievements. Yadav earned his doctorate at the Max Planck Institute for Solar System Research (MPS) and the Institute for Astrophysics at the Göttingen University. In his thesis, he investigated how magnetic fields are created in fast rotating low-mass stars with the help of computational models. For the first time, Yadav was able to explain the magnetic fields in these stars with the same physical processes as for the generation of the terrestrial magnetic field. Today, the Otto Hahn Medal was awarded by the annual general assembly of the Max Planck Society in Saarbrücken.

Everybody who has ever used a compass to determine the North direction relied on the terrestrial magnetic field. Similar to the bar magnet experiment back in school, the terrestrial magnetic field has a North Pole and a South Pole. In contrary to a solid bar magnet, the magnetic field of the earth’s interior originates from complex movements of electrically conductive liquids. These induce electric currents and thereby also a magnetic field. It appears on the earth’s surface and does not solely serve humans bus also, for example, migratory birds as guidance.

This mechanism is called the dynamo and it is likely the cause for the occurrence of magnetic fields in many objects in our universe. We know from observations that all planets except Venus possess a magnetic field or did so in the past. The magnetic field of the Sun has been known for a long time, and an increasing number of magnetic fields is observed in other stars as well. How do magnetic fields form in planets and stars and how similar are the processes that drive the fields in these widely different celestial bodies? This question was investigated by Yadav in his PhD thesis. “From my early school years I have been fascinated by how science helps us to better understand the world around us. I am delighted that now I am a scientist myself. Every new result that I find using simulating planets and stars in supercomputers gives me more energy to move forward and explore further.” stated the young Otto Hahn Medal laureate.

“The physical process, which led to the generation of the terrestrial magnetic field, have been investigated for a long time”, explained Professor Dr. Ulrich Christensen of the MPS who supervised the PhD thesis of Dr. Yadav. “In his thesis, Dr. Yadav has shown that the same mechanisms that drive the Earth’s dynamo and thereby the terrestrial magnetic field, also cause the magnetic fields in fast rotating low mass stars”, according to Christensen. Therefore, the same processes most likely lead to the generation of magnetic fields in these distinct celestial bodies.

Similar to our Sun, other stars also have dark spots on their surface. Often they are larger and more concentrated towards the poles than the sunspots of our central star. The spots form in regions of the star’s surface, in which the magnetic field is strengthened by convection currents in deeper layers. “With our computations we could model the formation of large star spots in the polar regions of fast rotating low-mass stars with the same processes as in the Earth’s dynamo,” explains Yadav. The formation of spots on the Sun’s surface can be well described by computer simulations, but not by using only the principles of the Earth’s dynamo. To fully explain the observations, further assumptions are required, such as a strong driving magnetic field in the interior of the Sun.

Dr. Rakesh Kumar Yadav studied physics at the Indian Institute of Technology Kanpur in India. He finished his PhD thesis at the MPS and the Institute for Astrophysics at Göttingen University in January 2015 after two years and eight months. Currently Dr. Yadav is a PostDoc fellow at the Harvard-Smithsonian Center for Astrophysics in the USA.

Roughly 7000 young scientists do their research at the 80+ Institutes of the Max Planck Society. The Otto Hahn Medal is awarded annually to young researchers for outstanding scientific achievements, which are usually linked to their PhD thesis. Since 1978, more than 900 young researchers have been awarded with the Medal.

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