Dos professors d'Enginyeria Física han publicat un article a Nature junt amb altres investigadors

The steady vision of a starry night is challenged by the unexpected appearance of cosmic beacons, stellar explosions that shed light and matter to space. Among the rich zoo of stellar explosions, classical novae have captivated the interest of astronomers for decades. They are produced in stellar binary systems consisting of two stars, each having the mass of our Sun but separated only by a distance of the order of the Earth-Moon orbit. In such conditions, mass transfer episodes ensue, with streams of matter flowing towards the most compact component of the system: a white dwarf star, an object of planetary size. The piling up of matter on top of the white dwarf turns out to be unstable and a thermonuclear-driven explosion takes place. In the event, 10-5 - 10-4 solar mass of nuclear processed material
are expelled. Astronomers have spectroscopically analyzed the composition of these ejected nova shells, unveiling an inhomogeneous distribution of chemical species whose origin has remained a puzzle for nearly half a century.

Now, an international team of researchers, from UPC-Barcelona (J. Casanova, J. Jose, E. Garcia-Berro), U Pisa (S.N. Shore) and Stony Brook U (A.C. Calder) have for the first time performed 3-D simulations of the mixing processes taking place at the core-envelope interface during classical novae. The simulations, published in Nature in october 2011, show that hydrodynamic (Kelvin-Helmholtz) instabilities are the likely origin of the inhomogeneous distribution of chemical species in the ejecta.

Snapshots of the development of Kelvin–Helmholtz instabilities at t = 151 s (a), 193 s (b), 296 s (c) and 379 s (d), shown in terms of the 12C mass fraction on a logarithmic scale