Herbig–Haro object

A luminous nebula produced when narrow jets from a young star shock and heat surrounding gas. Its knots and arcs mark places where outflows collide with interstellar material or earlier ejecta.

Protostellar jet: A narrow, fast outflow launched from a protostar or its surrounding accretion system. Its material drives the shocks that illuminate a Herbig–Haro object.
Protostar: A young stellar object still gaining mass from its natal cloud before sustained hydrogen fusion begins. Herbig–Haro objects are associated with outflows from stars at this early stage.
HH 1 and HH 2: A pair of Herbig–Haro objects in Orion, among the first such nebulae identified. Their opposing positions reveal a bipolar outflow from a young star.
Sherburne Wesley Burnham: An American astronomer who discovered a small nebula near the star T Tauri in 1890. His observation was later recognized as the first-known Herbig–Haro object.
Planetary nebula: An expanding shell of ionized gas shed by a low- or intermediate-mass star near the end of its life. It is also a glowing nebula, but comes from an evolved star rather than a protostar.
Bow shock: A curved shock wave formed as an object or flow moves supersonically through surrounding gas. The leading edge of a jet often creates this arc-shaped structure.
Star formation: The process by which dense regions of molecular clouds collapse to form stars and planetary systems. Herbig–Haro objects are visible signs of active star formation.
HH 34: A prominent Herbig–Haro system in Orion with a collimated jet and bright shock knots. Its resolved structure illustrates how variable ejection creates a chain of shocks.
George Herbig: An American astronomer who studied emission-line stars and published an early account of these nebulae in 1950. His independent study helped establish the objects as a distinct phenomenon.
H II region: A region of ionized hydrogen surrounding hot, young stars that emit ultraviolet radiation. Its gas is primarily ionized by starlight, unlike the shock-powered emission in these objects.

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