On the formation and properties of fluid shocks and collisionless shock waves in astrophysical plasmas

Antoine Bret, Asaf Pe’er

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


When two plasmas collide, their interaction can be mediated by collisionless plasma instabilities or binary collisions between particles of each shell. By comparing the maximum growth rate of the collisionless instabilities with the collision frequency between particles of the shells, we determine the critical density separating the collisionless formation from the collisional formation of the resulting shock waves. This critical density is also the density beyond which the shock downstream is field free, as plasma instabilities do not have time to develop electromagnetic patterns. We further determine the conditions on the shells initial density and velocity for the downstream to be collisional. If these quantities fulfil the determined conditions, the collisionality of the downstream also prevents the shock from accelerating particles or generating strong magnetic fields. We compare the speed of sound with the relative speed of collision between the two shells, thus determining the portion of the parameter space where strong shock formation is possible for both classical and degenerate plasmas. Finally, we discuss the observational consequences in several astrophysical settings.

Original languageEnglish
Article number905840311
JournalJournal of Plasma Physics
Issue number3
StatePublished - 1 Jun 2018
Externally publishedYes

Bibliographical note

Publisher Copyright:
© Cambridge University Press 2018.


  • Astrophysical plasmas
  • Plasma instabilities
  • Space plasma physics


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