The Dragon clash
NGC 5907 is a spiral galaxy lying in the Dragon constellation, showing extraordinary large loops and currents of stars in its surrounding halo. According to researchers, it could have been formed through a gigantic collision of galaxies, 8 to 9 billion years ago. Six scientists of the Observatoire de Paris, CNRS, Chinese Academy of Sciences, National Astronomical Observatories of China and Aix-Marseille Universite propose this scenario on the basis of simulations with 200 000 to 6 million particles. These up-to-date calculations, that include gas hydrodynamics, are able to reproduce in a film the formation of NGC5907 and its surrounding gigantic loops of matter. Results appeared on the cover of the online edition of Astronomy and Astrophysics, the 13 February 2012. They provide an important test for cosmological scenarios.