The Formation of Stellar Groups in Dense Cores of Molecular Clouds

Recent studies of nearby molecular clouds (Rho Ophiucus, Orion and Taurus) show that stars are preferentially forming in clusters within the dense gas cores of these complexes. This ``cluster mode" of star formation is a departure from the conventional line of thinking that argued a single core produced a single star. Observations of the molecular gas also suggest that on the relevant scales, magnetic effects are as significant as gravitational and thermal effects and thus discussion of the conditions and processes responsible for the formation of star clusters cannot ignore this important fact. We present here the results of an investigation into the effects of star formation and ambipolar diffusion on the stability of a molecular core composed initially of a uniform, magnetized gas and a pre-existing stellar population. The two components (gas and stars) are treated as fluids that are coupled through gravity and a prescribed mass transfer, or star formation rate (SFR). Our model assumes a SFR that depends on a critical density of molecular gas (rho_c ) such that for densities rho_g > rho_c , SFR ~ rho_g -rho_c and for rho_g <= rho_c , SFR =0. The gas fluid is assumed to be ``hot" compared to the stellar fluid: the gas has thermal, nonthermal, as well as mean field support while the stars retain only the thermal support of the gas that they condense out of. A linear stability analysis can identify the processes which are responsible for driving the system out of equilibrium and thus, instigating a burst of star formation. We have obtained both analytical (in the limit of small SFR and ambipolar diffusion) as well as full numerical solutions to the linear problem. We will discuss the results, which illustrate the individual as well as combined effects of ambipolar diffusion and mass transfer to the growth of instabilities in the two phase fluid.