AMBIPOLAR DIFFUSION IN ACTION: TRANSIENT C SHOCK STRUCTURE AND PRESTELLAR CORE FORMATION

作者：Chen Che Yu^*; Ostriker Eve C

来源：Astrophysical Journal, 2012, 744(2): 124.

DOI：10.1088/0004-637X/744/2/124

• ISM: magnetic fields
• magnetohydrodynamics (MHD)
• shock waves
• stars: formation

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 uses numerical integration to obtain a fitting formula for the shock thickness mediated by ambipolar diffusion, L-shock proportional to n(0)(-3/4)upsilon B-1/2(0)0(1/2)chi(-1)(i0). 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) similar to L-shock/upsilon(drift) similar to 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.

• 出版日期2012-1-10