Their results, obtained at the LULI in Paris, were published in the prestigious journal Nature Physics on Monday.
To investigate how X-rays can be emitted from a comet, a team of scientists from 15 research institutes performed experiments at the Laboratoire pour L'Utilisation des Lasers Intenses (LULI) in Paris where they replicated the interaction of the Solar-wind with a comet. The results of their experiment were analogous to many astrophysical systems, including the interaction of a comet with the solar wind.
In order to learn more about this mystery, the international group created a model system by firing laser beams onto a plastic foil. This caused the foil to explode which led to the expulsion of a stream of ions and electrons which formed a high speed flow of ionized gas like the Solar wind. The ionized gas, or plasma, then impacted onto a solid sphere placed nearly a centimeter away from the plastic foil. As the sphere represented a comet, the group could mimic what happens when a real comet passes through the Solar system and this generated some really interesting results. Notably, it was discovered that electrons are heated to about a million degrees in the upstream plasma by plasma turbulence. The team further concluded that these hot electrons are responsible for emitting X-rays, but they they only do so in the presence of a magnetic field.
CLF's Professor Bob Bingham led the STFC team involved in the project and said:
“These experimental results are important as they provide direct laboratory evidence that objects moving through magnetized plasmas can be sites of electron acceleration- a very general situation in astrophysics that takes place not only in comets, but also in planetary magnetospheres, such as our own Earth, or even in supernova remnants, where the ejected material moves across the interstellar gas. The experiments also confirm theoretical models developed by the team."
Throughout this impressive project the CLF team played a significant role; coming up with the scientific model for the interaction of the solar wind with the comet. This included conceiving the theoretical model for the generation of plasma turbulence, the acceleration of electrons by the turbulence and the X-ray emission from the accelerated electrons. Working in collaboration with scientists from the University of Oxford, the CLF team ran numerical simulations and were also responsible for the production of the laser target.
Other members of the CLF team involved included Chris Spindloe, Scitech Precision CSO and CLF Target Fabrication Program Leader and plasma physicist Dr Raoul Trines, who said the highlight of the project was reproducing a force of Nature;
“As a theorist I find it amazing that it is possible to sensibly replicate astrophysical phenomena in the laboratory, to test our physical understanding of what Nature gets up to," explains Raoul.
Chris Spindloe also added "It is always satisfying to see the results of the complex target manufacture that we carry out. Even more so when we are able to, through the CLF spin out Scitech Precision Ltd, enable high quality experiments across the world. The opportunity to work and collaborate with such an excellent team to achieve ground breaking results I know is one of the main reasons that the Target Fabrication team put so much time, effort and pride into the micro-engineered targets that are used in these experiments."
Figure 1 – Explaining the interaction of a comet with the solar wind and the generation of a suprathermal electron population.
The research was supported by EPSRC, STFC, AWE plc and the European Research Council.
The full publication is available to view in Nature Physics.
A news article covering this piece of research was featured in phys.org
For further information about the research, please contact Alexandra Rigby (Alexandra.rigby@physics.ox.ac.uk)
