Although the extreme conditions specific to astrophysical and geophysical environments cannot all be reproduced in the laboratory, the magnetic field observed shows remarkable similarities with magnetic fields observed in the cosmos. The findings represent a significant advance in the understanding of the mechanisms at work in the formation of natural magnetic fields. They are published in Physical Review Letters dated 26 January 2007.
Most of the astrophysical objects which surround us (planets, stars and galaxies) have a magnetic field, whose origin is poorly understood. Such magnetic fields can play a major role in the evolution of various structures throughout the Universe. The Earth's magnetic field, which is very probably caused by the movement of liquid iron in the core, not only makes compass needles point north, but also protects us from the harmful effects of cosmic rays and the solar wind.
As early as 1919, Larmor put forward the hypothesis that the Sun's magnetic field is generated by a "dynamo" effect, in other words by the movement of a fluid that conducts electricity. Because of their highly chaotic (turbulent) nature, the analysis of geophysical and astrophysical flows is beyond the current capacities of numerical simulations, and, until now, has thwarted all attempts at a theoretical approach. It is only through experimental work that it is possible to reproduce the dynamo phenomenon with parameters that are similar to those that occur naturally. Following experiments carried out in 2000 by teams in Riga and Karlsruhe, the challenge facing the physicists was to show that the fully turbulent motion of a conducting liquid could spontaneously generate a magnetic field.
1 Von Karman (the physicist after whom the flow that was created was named), Sodium (the liquid used in the experiments)
2 Department of condensed state physics at CEA, team led by François Daviaud
3 Physics laboratory of the Ecole normale supérieure at Lyon, (CNRS, ENS Lyon), team led by Jean-François Pinton
4 Laboratory for statistical physics at the Ecole normale supérieure, (CNRS, ENS Paris, Universités Paris VI and Paris VII), team led by Stephan Fauve5 The VKS experiment was carried out at CEA/Cadarache, at the Department of nuclear technology, Office of nuclear energy
Since 1998, the VKS collaboration has been studying a highly turbulent flow produced by the movement of two turbines revolving in opposite directions in a cylinder filled with liquid sodium5. Liquid sodium is an excellent conductor of electricity, while having a density similar to that of water, unlike many other metals which are much denser. In September 2006, the VKS2 experiment showed that, when the turbines revolve faster than a critical speed (1020 rpm), the flow spontaneously generates a magnetic field. This is the first time that such results have been observed in a highly turbulent medium.
The result proves that fluid dynamos continue to operate in the presence of strong turbulence of the kinds that occur under natural conditions. The achievement of the dynamo experiment under laboratory conditions opens up many new prospects. In particular, it will make it possible to study the energy balance involved in the production of a magnetic field as well as its dynamics. It may therefore be possible to understand the origin of the pseudoperiodic oscillations in the solar cycle or the irregular reversals of the Earth's magnetic field.
Monica McCarthy | EurekAlert!
Study offers new theoretical approach to describing non-equilibrium phase transitions
27.04.2017 | DOE/Argonne National Laboratory
SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
27.04.2017 | Life Sciences
27.04.2017 | Physics and Astronomy
27.04.2017 | Earth Sciences