Herbig–Haro objects (HH) are small patches of nebulosity associated with newly born stars, and are formed when narrow jets of gas ejected by young stars collide with clouds of gas and dust nearby at speeds of several hundred kilometres per second. Herbig–Haro objects are ubiquitous in star-forming regions, and several are often seen around a single star, aligned along its rotational axis.
HH objects are transient phenomena, lasting not more than a few thousand years. They can evolve visibly over quite short timescales as they move rapidly away from their parent star into the gas clouds in interstellar space (the interstellar medium or ISM). Hubble Space Telescope observations reveal complex evolution of HH objects over a few years, as parts of them fade while others brighten as they collide with clumpy material in the interstellar medium.
The objects were first observed in the late 19th century by Sherburne Wesley Burnham, but were not recognised as being a distinct type of emission nebula until the 1940s. The first astronomers to study them in detail were George Herbig and Guillermo Haro, after whom they have been named. Herbig and Haro were working independently on studies of star formation when they first analysed Herbig–Haro objects, and recognised they were a by-product of the star formation process.
Read more about Herbig–Haro Object: Discovery and History of Observations, Physical Characteristics, Numbers and Distribution, Proper Motions and Variability, Source Stars, Infrared Counterparts (MHOs)
Other articles related to "objects":
... Herbig–Haro (HH) objects associated with very young stars or very massive protostars are often hidden from view at optical wavelengths by the cloud of gas ... Such deeply embedded objects can only be observed at infrared or radio wavelengths, usually in the light of hot molecular hydrogen or warm carbon monoxide emission ... revealed dozens of examples of "infrared HH objects" ...
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