Looney, Leslie W. Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana, Illinois.
Last reviewed:December 2019
- Ionized jets and molecular outflows
- Role in star formation
- Related Primary Literature
- Additional Reading
Compact nebulae with peculiar spectra that were first studied in the 1950s by George Herbig and, independently, by Guillermo Haro. Herbig-Haro (HH) objects are small patches of nebulosity with highly variable luminosity typically located within or adjacent to star-forming regions. They exhibit spectroscopic emission lines characteristic of highly ionized gas that has been shocked upon interaction with the surrounding interstellar medium. Doppler shifts of the spectral lines reveal that the gas is moving at supersonic velocities of 100 km/s (60 mi/s) to more than 1000 km/s (600 mi/s). Typical masses of an individual clump of gas are 1–20 times that of Earth with temperatures of 8000–12,000 K. Like the interstellar medium, they are composed almost entirely of hydrogen and helium with less than 1% heavier elements. See also: Astronomical spectroscopy; Doppler effect
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