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

Journal Article · Tue Jan 10 04:00:00 EST 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/744/2/124· OSTI ID:22004267

Cheyu, Chen

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{sub shock}{proportional_to}n{sub 0}{sup -3/4} v{sub 0}{sup 1/2} B{sub 0}{sup 1/2}{chi}{sub i0}{sup -1}. 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{sub AD} {approx} L{sub shock}/v{sub drift} {approx} 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.

• OSTI ID: 22004267
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 744; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
AMBIPOLAR DIFFUSION
COMPUTERIZED SIMULATION
ION COLLISIONS
IONIZATION
MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETOHYDRODYNAMICS
SHOCK WAVES
STAR EVOLUTION
STARS
TIME DEPENDENCE