HST image of HH34
Machine-gun-like blast of "bullets" of dense gas ejected from HH34 protostar at speeds of one-half million miles per hour, 1,500 light-years away near the Orion Nebula. (HST image, J.Hester, Arizona State University, 1995)

Object associated with High Velocity Molecular Gas (HVMG) near Young Stellar Objects (YSO) in star forming regions have been described in many different ways :

Image of HH34S Optical Jet
Another image of HH34 in the forbidden [SII] emission line, has a striking resemblance to quasar jets (Calar Alto, Mundt, 1989).

Associated with Young Stellar Objects (YSO) are High Velocity Molecular Gas (HVMG), Herbig-Haro (HH) objects and optical jets. The molecular gas outflows velocities are typically 5 to 20 km/s, but the optical jets and their associated Herbig-Haro objects have radial velocities up to 450 km/s with opening angles as narrow as one degree. The very high speed gas associated with the optical jets are what drive the High Velocity Molecular Gas.

The optical jet associated with the Herbig-Haro object HH34S is about 30 arcseconds long, but it terminates over a hundred arcseconds further downstream in a bow shock which resembles quasar lobes. Bow shocks and bright knots are usually associated with the end of YSO jets. Many knots shows up, (letters A through L in above figure), their outward motion has been detected in recent HST images which suggests episodic bursts from the protostar.

Image of 3C 273 Radio+Optical Jet
Radio and optical image of jet from quasar 3C 273, very similar to optical jet of HH 34S. (Bahcall et al., 1995)

Nearly all jets aren't straight but show changes in direction or wiggles, indicating that the protostar is wobbling, perhaps from the gravitational influence of a nearby stellar companion or planetary system. This effect is plainly visible in the helical twist of the jet from quasar 3C 273. (this helical morphology is also visible in the star SS 433)

Movie of HH30 Jet Motions

HH 30 Jet Evolution

Movie of HH 30 jet motions over the span of a year reveals that the bright knots are 'spurts' from episodic bursts from the protostar (obscured by a dark band of dust between the two largest streaks). (C.Burrows, K.Stapelfeldt, A. Watson, 1995)

HST Image of HH47
HH 47 : Large scale view of bowshocks created when jets plow out a cavity in the interstellar medium about 1,500 light years away in the constellation vela near the Gum Nebula. (J. Morse/STScI, and NASA, 1995).

There is remarkable resemblence to quasar Cygnus-A especially of the arrowhead bowshock of HH 1/2. There are nearly 300 identified Herbig-Haro objects, many more are expected to be discovered in nearby stellar nurseries. Although they have been known since the early 1950's it is only recently with the advent of infrared astronomy and the discovery of young stellar objects that their true nature has been recognized.

Rodriguez et al. (1994) have determined that about a third of these objects are detected in the radio continuum, the optical jet of the source in the HH 111 region is well aligned with a one-sided radio jet. (see also Cernicharo and Reipurth, 1996)

Recently López et al. (1995) have detected a 14 arcminute bipolar structure in planetary nebula KjPn8 using the 2.1 meter telescope at Mexico's San Pedro Mártir. The convoluted nebulosity 13 light year in size is interpreted as originating from precessing jets produced by episodic outbursts from the central star. Such collimated outflows are identical to young stellar objects and have been detected in several other planetary nebulae such as the cat's eye. The astronomers were puzzled by the presence of bright knots of shocked gas in KjPn8 which are identical to Herbig-Haro objects which are normally associated with young stellar objects, here we find them in a dying star !

Also, jet-like extensions have been found in several planetary nebula such as M2-9. (Balick, 1989; consult the last six references at the end of this page).

Jet have been detected in quasars and in many other galactic objects such as SS433, GRS 1915-105 and GRO J1655-40 which have often been referred to as 'mini-quasars'.

These recent observations of jets only emphasizes the continuity of properties common to all jet emitting objects within the galaxy.


  1. Catalog of Herbig-Haro Objects. Complete references and links to abstracts.
  2. Star Formation Newsletter
  3. [ NEW ]Astrophysical jet simulation
  4. [ NEW ]Computational Techniques in Astrophysical Gas Dynamics
  5. Bipolar Jet and Lobes
  6. Recent Hubble images of YSO jets (HH1/2,30,34,47)
  7. Chandler,C.J., Koerner,D.W., Sargent,A.I., Wood,D.O.S.: 1995, ApJ., 449, L139. Disk and Envelope of HH 24 MMS (VLA at 43.3 GHz)
  8. Ogura,K.: 1995, ApJ., 450, L23. Bow Shock Pairs Associated with HH Jets (Halpha,[S II] Images of HH1/2, HH124; spectrum of HH1/2)
  9. Mundt,R.: 1989, in The Physics and Chemistry of Interstellar Molecular Clouds, mm and Sub-mm in Astrophysics, p.152.
  10. López,J.A., Vázquez,R., Rodríguez,L.F.: 1995, ApJ., 455, L63. (Bipolar, Rotating, Episodic Jet in KjPn 8)
  11. Rodriguez,L.F., Reipurth, Bo: 1994, Astron.Astrophys., 281, 882.
  12. Reipurth,B., Heathcote,S.: 1995, Sky and Telescope, Oct p.38.
  13. Cernicharo,J., Reipurth,B.: 1996, ApJ., 460, L57. HH 111 CO radio jets, flows and bullets.
  14. Bahcall,J.N., Kirhakos,S., Schneider,D.P., Davis,R.J., Muxlow,T.W.B., Garrington,S.T., Conway,R.G., Unwin,S.C.: 1995, ApJ., 452, L91. Combined Radio and Optical images of 3C 273 jet (HST/MERLIN) (see also LALN preprint)
  15. Zhang,Q., Ho,T.P.P., Wright,M.C.H., Wilner,D.J.: 1995, ApJ., 451, L71. SiO Emission in a Jetlike Molecular Outflow toward L1157
  16. Balick,B., Preston,H.L., Icke,V.: 1987, ApJ., 94, 1641. Spectral images of PN NGC 40 and NGC 6543
  17. Latter,W.B., Hora,J.L., Kelley,D.M., Deutsch,L.K., Wynn-Williams,C.G.: 1993, AJ., 106, 260. (near IR pictures of AFGL 2688 or 'Egg Nebula' in I Band and K Band, page 2 is contour plot of I band fig3)
  18. Planetary Nebula M2-9 (IR picture). from Hora,J.H., Latter,W.B.: 1994, ApJ, 437, 281. Near IR J,H,K (2.12, 2.16, 2.26 microns) pictures of M2-9 or M2-9 'true color' image (first image is blue=J,green=H,red=K; second image is red=H2, green=Brackett gamma)
  19. Near Infrared Spectroscopy of M2-9 and M1-92 - Two Young Bipolar Planetary Nebulae
  20. Bruce Balick's Planetaries (has image of M2-9)
  21. May 14, 1995 The AGB Newsletter (article on M2-9)
  22. Icke,V., Preston,H.L., Balick,B.: 1989, ApJ., 97, 476. M2-9 : Planetary Nebula with an Eruptive Nucleus
  23. Balick,B.: 1989, ApJ., 97, 476. The Evolution of PN. (picure of jet-like M2-9 and spectral morphology of H-alpha and [N II] lines)
  24. Adam,F., Garrlelt,M. : 1996, ApJ. 472, 684. Hydrodynamical Models of Outflow Collimation in Young Stellar Objects
  25. The Gas Dynamics of Stellar Wind Blown Nebulae

(iso-contour map courtesy of Reinhart Mundt, Max-Plank-Institut fur Astronomie)
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