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"Siphoning" of a star: reconstitution by laser

​The extreme physical phenomena observed in two-star systems, qualified as "magnetic cataclysmic variables", have been successfully reproduced in a laboratory by an international project team. In these systems, a "white dwarf", an extremely dense star, sucks in the matter from a nearby second companion star, which then emits high energy radiation when it hits the surface of the dense star. To perform this spectacular astrophysics experiment, the scientists made use of the powerful Orion Laser Facility in the UK to evaporate a millimetre size target and produce a hot plasma flow equivalent to those that occur at the poles of a white dwarf. The project team, which combined the skills of the CEA, the Ecole polytechnique, CNRS, the Observatoire de Paris the Université Paris Diderot and the Université Pierre and Marie Curies, has published its results in Nature Communications on Monday 13 June.

Published on 14 June 2016

​White dwarfs are very high-density stars that often have a very strong magnetic field; they can sometimes absorb the matter from nearby companion stars.  This matter is then concentrated and captured by the white dwarf, channelled in a very narrow region above its magnetic pole, thus forming accretion columns with dimensions typically from 100 to 1000 kilometres. These areas are far too small to be observed directly using telescopes. To study the physical phenomena that occur around the magnetic pole of the white dwarf, the researchers needed to reproduce them in a laboratory.

To this end, for a few nanoseconds, they concentrated all the energy from the Orion laser on a surface of a few square millimetres. They were then able to produce a hot plasma flow moving at a velocity of 200 km/s. When this plasma flow struck a steel obstacle, it mimicked the same phenomena that occur at the surface of white dwarfs. By employing a second laser beam, they were able to use X-rays to probe the dynamic of the accretion column. This experiment, the first of its kind anywhere in the world, made it possible to produce a laboratory model of an astrophysical object.

Better understanding of white dwarfs and their dynamics is crucial for astrophysicists and cosmologists because they are considered as the possible progenitors of thermonuclear supernovae, celestial bodies used to measure the expansion of the Universe.  Experiments of this kind could be boosted in the near future by a far more powerful LMJ laser.

About high-power lasers

Orion is a laser facility based in the United Kingdom, managed by the Atomic Weapons Establishment (AWE). It combines 10 long-pulse beams (nanosecond scale, 10-9 s) and two ultra-short beams (less than picoseconds, 10-12 s). This type of experiment, which first began a few years ago at the Luli200 facility (Laboratoire pour l'utilisation des lasers intenses) at the École Polytechnique, could soon benefit from much more powerful LMJ and Petal lasers. The LMJ-Petal facility (in the Gironde region) is coordinated by the CEA and will combine the 176 beams from the laser Megajoule with the Petal petawatt beam.​

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