The magnetic geometry of pulsed astrophysical jets

Hypersonic, highly collimated, mass outflows (jets) are a ubiquitous phenomena in astrophysics. While the character of the jets differ, many exhibit some form of quasi-periodic clumping indicating the jet source is episodic or pulsed. The presence of pulsed jets in so many astrophysical contexts suggests a common formation mechanism. Such a process seems to have been found in magnetocentrifugal launching, the combination of magnetic and centrifugal forces that occurs when a magnetized gaseous accretion disk orbits a central gravitating source. Observations of strong magnetic fields in jets are, however, rare or indirect. Thus, the presence and effects of magnetic fields in young stellar object (YSO) jets remains an unresolved issue of the highest importance. In this Letter we focus on what should be expected for the structure of the fields in pulsed YSO jets. We show that combining velocity variability with an initial field configuration consistent with collimated, magnetocentrifugally launched jets leads to a clear set of predictions concerning the geometry and relative strength of the magnetic field components in evolving YSO (and perhaps other) jets.