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Spherical galaxies are more stable Are galaxies stable? Although it is impossible to answer this question in the general case, mathematicians have now shown that spherical galaxies described by what are known as Vlasov-Poisson equations maintain their overall shape and properties, even when they are disturbed. To achieve this result, the researchers developed new tools that should enable them to study the stability of broader classes of galaxy. Inventiones Mathematicae January 2012 52 A universal mechanism that explains the formation of satellites around planets A new model for the formation of satellites, already used successfully to describe the formation of Saturn’s moons, has been tested on other planets in the Solar System. According to the researchers’ calculations, the formation and distribution of the many satellites orbiting gas giants is due to the spreading of their massive planetary rings. In addition, this also explains why planets like Earth and Pluto have only one moon. This general mechanism may also apply to other planetary systems. Science November 2012 Elucidating the mysterious origin of magnetic fields in the universe For the first time, physicists have succeeded in reproducing in the laboratory one of the mechanisms that gave rise to magnetic fields in protogalaxies. The researchers used a laser pulse to generate a shock wave similar to those produced in the universe during the pre-galactic era that preceded the formation of galaxies. They observed that the values of the magnetic fields recorded during the experiment were consistent with those provided by recent astrophysical observations. Their work opens the way to the experimental study of as yet poorly understood astrophysical phenomena. Nature January 2012 online Artist’s impression showing that, on average, there is at least one planet per star in the Milky Way, and that low-mass planets (bluish hue) are more common than gas giant planets (orange hue). One planet for every star in the Milky Way There are probably as many extrasolar planets in our galaxy as there are stars. This is the conclusion of a statistical study based on the observation of millions of stars using the gravitational microlensing method. The study also shows that around two thirds of the stars in the Milky Way host super-Earths, planets similar to ours but with masses five to ten times greater. Numerous Earth-like planets could therefore be discovered in the near future. Nature January 2012 online Did extraterrestrial nitrogen cause the emergence of life on Earth? A study has shown that the reactions that generate molecular nitrogen (N2) in interstellar clouds are far less efficient than previously thought. Using modified simulations of these very low-temperature clouds of gas and dust, researchers have concluded that only 10-20% of the nitrogen was produced there as N2. The rest of the nitrogen remained in the atomic state and probably became bound to the surface of dust particles, where it reacted with hydrogen, forming NH3. This NH3 may then have been transported to Earth by meteorites, providing the nitrogen present in the first prebiotic molecules. Proceedings of the National Academy of Sciences June 2012 online A year at CNRS 2012


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