A small nebula with an emission-line spectrum, found in regions of star formation. HH objects have high velocities of several hundred kilometres per second relative to their surroundings. They are believed to be bow shocks formed when fast-flowing jets of material from a young star encounter interstellar matter. The emission lines result from the recombination of ions and electrons in the cooling gas behind the bow shock. They are named after the American George Howard Herbig (1920– ) and the Mexican Guillermo Haro (1913–88).
Subjects: Astronomy and Astrophysics.