Ambipolar diffusion in action: Transient c shock structure and prestellar core formation

Che Yu Chen, Eve C. Ostriker

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


We analyze the properties of steady and time-dependent Cshocks under conditions prevailing in giant molecular clouds. For steady Cshocks, 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 αn0 -3/4 v 0 1/2 B 0 1/2χi0 -1. Our formula also agrees with an analytic estimate based on ion-neutral momentum exchange. Using time-dependent numerical simulations, we show that Cshocks 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 ∼ Lshock/v drift ∼ 0.1-1Myr. 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 Cshocks.

Original languageEnglish (US)
Article number124
JournalAstrophysical Journal
Issue number2
StatePublished - Jan 10 2012
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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


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