Herbig Haro objects


Herbig-Haro objects are small nebulous patches that form when a outflowing jet from a T-Tauri or Herbig AeBe star collides with the slow moving interstellar medium (ISM). For this reason they are associated with starforming regions and young stellar objects (YSO's) and are aligned with the star along its rotational axis (perpendicular to the accretion disk of the star). Temperatures in HH objects range from 8000 to 12000 K and density ranges from 2000 to 20000 particles per cm^3. Most of them can be found within 0.5 parsecs from its parent star. Each working surface or HH object in the jet has 2 shocks. The jet decelerates in a mach disk and the ISM accelerates in a bow shock. Heat is created through this proces (radiative cooling) and the object can be seen as a type of emission nebula.
The ionized jets that form these objects can only be found when a accretion disk is present. Advection and convection of material in the disk create a poloidal magnetic field and the infalling material gets flung along this field in the direction of the rotational axis of the star. A field inside the jet further collimates the outflow. The jet can accelerate due to the density gradient and the poloidal magnetic field. The jets are important for planetary formation because they remove excess angular momentum, thus stabilizing the rapidly spinning star and its accretion disk.

Herbig Haro objects

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