NGC 1333 is catalogued as a reflection nebula but is actually a diverse region and part of the Perseus OB2 molecular cloud complex. It is one of the nearest star forming regions and particularly rich in young stellar objects (YSOs). Stellar clusters are born embedded within molecular clouds and during their early evolution as YSOs are often only visible at infrared wavelengths, being heavily obscured by dust. Four classes of young stellar objects have been described. Class I though III objects progress through an evolutionary sequence of being less dust enshrouded, as they develop towards the zero-age main sequence. The earliest and most imbedded stage of star formation is the class 0 YSOs. These earliest protostars are difficult to detect due to their heavily imbedded nature. Less than 50 Class 0 objects are known however 4 of these low mass protostars exist in NGC 1333. Also 36 Herbig-Haro obejects have been identified in NGC 1333 confirming its status as a young active region of star formation. Herbig-Haro objects are collisionally excited nebulae produced by outflows ejected by YSOs. They are produced mainly during the first few hundred thousand years of life of a YSO and are usually highly obscured by the cloud core environment from which they formed.
The gaseous structure of NGC 1333 has been mapped at radio wavelengths and appears to support the large scale star formation observed. Lumpy and filamentary cloud structure exists in NGC 1333 indicative of recent collapse and fragmentation of the parent molecular cloud leading to the clustered mode of star formation observed in the nebula. In addition a series of cavities and shells exist presumably blown out by the outflows of infant protostars. Infrared surveys reveal the presence of YSOs at the edge of these cavities indicating that sequential star formation has occurred there and has been triggered by the effects of the powerful outflows from the first generation of stars. The entire process is extremely recent as the cloud hosting NGC 1333 is less than a million years old.'