article for September 21, 2019

Article of the day for September 21, 2019 is Herbig–Haro object.
Herbig–Haro objects are bright nebular patches formed when narrow jets of partially ionized gas ejected from newborn stars collide with clouds of gas and dust. Often aligned with a star's rotational axis, they are commonly found in star-forming regions. Most of them lie within a few light-years of the source. They are transient phenomena, lasting around a few tens of thousands of years. They can change visibly over just a few years, as they move rapidly away from their parent star. First observed in the late 19th century by Sherburne Wesley Burnham, Herbig–Haro objects were not recognized as distinct from other emission nebulas until the 1940s. The first astronomers to study them in detail were George Herbig and Guillermo Haro, who independently recognized that the objects were by-products of the star formation process. Although the objects emit visible wavelengths, many are hidden by dust and gas, and can only be seen at infrared wavelengths.