HH 1/2

Lore & Background

HH 1/2 were discovered by George Herbig and Guillermo Haro and were the first objects to be identified as Herbig-Haro objects. They are located about 1343 light-years away in Orion, near NGC 1999.

The pair comprises two oppositely oriented bow shocks separated by 2.5 arcminutes, with a projected separation of about 1.1 light-year. HH 1/2 were the first Herbig-Haro objects with detected proper motion, and HH 2 was the first Herbig-Haro object detected in X-rays. Some structures within these objects move at speeds of 400 km/s.

The central region contains an opaque cloud core with an astrophysical jet and a highly embedded multiple-star system that remains invisible below 3 microns. These sources were first detected with the Very Large Array and are named VLA 1 and VLA 2.

The source HH 1-2 VLA 1 drives the HH 1/2 pair, while VLA 2 drives the Herbig-Haro objects HH 144/145. There might be a third outflow in the central region, indicating a third member. The jet toward HH 1 is visible in optical images, while the counterjet toward HH 2 was detected in the infrared with the Spitzer Space Telescope.

Reader's Guide

HH 1/2 holds a foundational place in the study of Herbig-Haro objects as the first recognized pair, establishing the class. Their discovery by Herbig and Haro marked the beginning of systematic identification of these shock features. As the first Herbig-Haro objects with detected proper motion, they provided direct evidence of high-speed outflows from young stellar objects. HH 2's detection in X-rays was a milestone, revealing that these objects emit across the electromagnetic spectrum beyond optical and infrared.

The central region's embedded multiple-star system, detected only at radio wavelengths via the Very Large Array, underscores the complexity of the driving sources. The detection of the counterjet toward HH 2 in the infrared by Spitzer demonstrated that parts of these outflows can be obscured at optical wavelengths. The possibility of a third outflow suggests that the region may host more than two young stellar objects, adding to the dynamical richness of the system. HH 1/2 remains a benchmark for understanding jet-driven shocks and the interaction of protostellar outflows with the interstellar medium.