What is the primary composition of Herbig-Haro objects?

Herbig-Haro objects are primarily composed of jets of gas, typically created by young, newly formed stars. These objects are formed when the jets of materials ejected from a star interact with surrounding interstellar material. As the high-velocity jets collide with this material, they generate shock waves that heat the gas and dust in the region, causing it to emit light.

The jets themselves consist mostly of ionized hydrogen and other elements, and their interactions can create bright, often multi-colored regions visible in various wavelengths, including optical and infrared light. These dynamic processes are key to understanding star formation and the surrounding environments of young stellar objects.

Other choices like hot gases may be found as a result of the jets interacting with the surrounding medium, but the fundamental characteristic of Herbig-Haro objects is distinctly the jets of gas. Cool liquids, dust, and ice do not play a primary role in the formation and defining characteristics of Herbig-Haro objects, as they are not the main contributors to their visibility and dynamics in the cosmos.