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arXiv · 1110.1638

Ambipolar Diffusion in Action: Transient C shock Structure and Prestellar Core Formation

Che-Yu Chen·Eve C. Ostriker
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Abstract

We analyze the properties of steady and time-dependent C shocks under conditions prevailing in giant molecular clouds. For steady C shocks, we show that ionization equilibrium holds and use numerical integrations to obtain the shock thickness mediated by ambipolar diffusion as a function of density, inflow velocity, magnetic field, and ionization fraction in the cloud. Our formula also agrees with an analytic estimate based on ion-neutral momentum exchange. Using time-dependent numerical simulations, we show that C shocks have a transient stage when the neutrals are compressed much more strongly than the magnetic field. The transient stage has a duration set by the neutral-ion collision time, t_AD ~ L_shock/v_drift ~ 0.1 - 1 Myr. This transient creates a strong enhancement in the mass-to-magnetic flux ratio. Under favorable conditions, supercritical prestellar cores may form and collapse promptly as a result of magnetic flux loss during the transient stage of C shocks.

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Che-Yu Chen, Eve C. Ostriker. 2011-10-07. Ambipolar Diffusion in Action: Transient C shock Structure and Prestellar Core Formation. https://doi.org/10.1088/0004-637x%2F744%2F2%2F124

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