Numerical and experimental study of magnetized accretion phenomena in young stars

Newly formed stars accrete mass from the circumstellar disc via magnetized accretion funnels that connect the inner disc regions to the star. The ensuing impact of this free-falling plasma onto the stellar surface generates a strong shock, whose emission is used as a proxy to determine the accretion rates. Observations show that the X-ray luminosity arising from the shock heated plasma at the base of accretion columns is largelybelow the value expected on the basis of optical/UV observations. As a result, current 2D numerical simulations matching X-ray accretion rates cannot reproduce optical accretion rates. To understand the impact of accretion flows on the stellar surface in the presence of a strong magnetic field we have developed laboratory experiments reproducing crucial aspects of the accretion dynamics in Young Stellar Objects. As a model of accretion columns, we use laser-produced super-Alfvenic magnetically confined jets [,4] to collide them on solid targets. Here we present results from these experiments and from multi-dimensional MHD simulations.\newline $[1] Curran et al. 2011, A{\&}A 526, A104\newline [2] Orlando et al. 2010, A{\&}A 510, A71\newline [3] Albertazzi B., et al., Science 346, 325 (2014)\newline [4] Ciardi A., et al. Phys. Rev. Lett. 110, 025002 (2013)