NGC 1333 is a reflection nebula located in the northern constellation Perseus, positioned next to the southern constellation border with Taurus and Aries. It was first discovered by German astronomer Eduard Schönfeld in 1855. The nebula is visible as a hazy patch in a small telescope, while a larger aperture will show a pair of dark nebulae designated Barnard 1 and Barnard 2. It is associated with a dark cloud L1450 (Barnard 205). Estimates of the distance to this nebula range from 300 –. This nebula is in the western part of the Perseus molecular cloud and is a young region of very active star formation, being one of the best-studied objects of its type. It contains a fairly typical hierarchy of star clusters that are still embedded in the molecular cloud in which they formed, which are split into two main sub-groups to the north and south. Most of the infrared emission is happening in the southern part of the nebula. A significant portion of the stars seen in the infrared are in the pre-main sequence stage of their evolution. The nebula region has a combined mass of approximately 450 solar mass, while the cluster contains around 150 stars with a median age of a million years and a combined mass of 100 solar mass. The average star formation rate is 1e−4 yr–1. Within the nebula are 20 young stellar objects producing outflows, including Herbig–Haro objects, and a total of 95 X-ray sources that are associated with known members of embedded star clusters. In 2011 researchers reported finding 30 to 40 brown dwarf objects in the cloud and in the Rho Ophiuchi cloud complex. 15 objects with a spectral type of M9 or later were discovered in NGC 1333. This spectral type corresponds to a mass of a planetary-mass object (PMO) at the age of NGC 1333. About 42% of the PMO are surrounded by a circumstellar disk, but only one out of six objects with a spectral type of L0 (about 10 ) or later has a disk. Scholz et al. argues that this indicates that very low mass PMOs form like planets (aka ejected planets) and not like stars (also called sub-brown dwarfs). Parker & Alves de Oliveira on the other hand argue that the distribution of PMOs in NGC 1333 follows N-body simulations of objects that form like stars and that none of the PMOs has a peculiar motion, which is predicted for ejected planets. They also note that ejected planets are hiding in this and other star-forming regions. Additional PMOs were discovered by Scholz et al. 2012 with Subaru (e.g. SONYC-NGC1333-36 with estimated 6 ) and by Langeveld et al. 2024 with JWST (6 objects and one JuMBO candidate). Langeveld et al. did not find any object below 4, despite JWST being sensitive enough to detect these objects. This could mean that star-formation does not occur below 4, which is consistent with previous observations in most star-forming regions and the nearby stellar population. One source, called NIRISS-NGC1333-5 (NN5), shows infrared excess, which is an indication of a disk around the object. With a mass of 5, this object could be one of the lowest mass object with a disk known so far.

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