HH 46/47
A protostellar jet complex that revealed the nature of Herbig–Haro objects.
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HH 46/47 is a complex of Herbig–Haro objects located about 450 parsecs (1,470 light-years) away in a Bok globule near the Gum Nebula. It is one of the most studied HH objects and was the first jet to be associated with young stars, discovered in 1977. The complex includes four emission nebulae (HH 46, HH 47A, HH 47C, HH 47D) and a jet (HH 47B), along with a mostly unipolar molecular outflow and two large bow shocks on opposite sides of the source star.
Lore & Background
The object was discovered in 1977 by American astronomer R. D. Schwartz, who named the two nebulae HH 46 and HH 47 as the 46th and 47th HH objects. The jet and other nebulae were soon identified. This was the first jet discovered near a protostar, resolving a debate: prior models suggested HH objects were reflection nebulae, but Schwartz had theorized in 1975 that they were produced by radiative shocks from stellar winds. The discovery of the jet in HH 46/47 confirmed that HH objects are shock-driven emission nebulae powered by jets ejected from protostars.
The source is a binary class I protostar inside a dark cloud, undetectable at visual wavelengths. It ejects material at about 150 km/s into a bipolar jet. Only one jet is visible at visual wavelengths; the counterjet is hidden by the dark cloud but is clearly seen in infrared.
The jet is twisted and bent due to precession of the source star. Variations in eruptions cause shocks within the jet, making it visible. The complex spans 0.57 parsecs from HH 47C to HH 47D on the sky plane, with two large bow shocks (HH 47SW and HH 47NE) each about 1.3 parsecs from the source, giving a total sky-plane length of 2.6 parsecs; the actual length is about 3 parsecs due to a 30° projection angle.
Reader's Guide
HH 46/47 is significant because its discovery of a collimated jet from a young star fundamentally changed the understanding of Herbig–Haro objects. Before this, it was unclear whether HH objects were reflection nebulae or shock-driven; the jet provided direct evidence that they are emission nebulae powered by protostellar outflows. The complex is one of the most studied HH objects due to its brightness, collimated jet, and impact on the field.
Its episodic eruptions, precessing jet, and molecular outflow offer insights into star formation and accretion processes. The object continues to be observed across wavelengths, with infrared images from the James Webb Space Telescope and spectra from the Spitzer Space Telescope revealing details of the source, jet, and surrounding molecular envelope. An image of a Question Mark associated with the object was reported in August 2023.
Frequently Asked Questions
What exactly is HH 46/47?
HH 46/47 is a cluster of Herbig–Haro objects — glowing knots of gas lit up by a young star's energetic outflows — nestled inside a dense Bok globule near the Gum Nebula. The whole complex stretches about three parsecs (roughly ten light-years) and sits approximately 1,470 light-years from Earth.
Who discovered HH 46/47 and why was that discovery a big deal?
R. D. Schwartz identified the complex in 1977, and it immediately stood out as a landmark in young-star research. It was the first protostellar jet ever clearly linked to a forming star, which gave astronomers their best early evidence for what Herbig–Haro objects actually are.
How fast is the HH 47B jet material moving?
The jet in HH 47B plows through the surrounding gas at roughly 150 km/s. That velocity is what carves the two dramatic bow shocks flanking the central young star and drives the one-sided molecular outflow observed in the complex.
Why do astronomers keep returning to HH 46/47 for research?
Because it was the first jet unambiguously tied to a protostar, it became the go-to benchmark for testing models of outflow and shock physics in young stellar environments. Its well-mapped mix of emission knots, bow shocks, and a unipolar flow makes it a natural laboratory for studying how forming stars eject material and sculpt their natal clouds.
More in Emission, Dark and Reflection Nebulae
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: HH 46/47 (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
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