An international team of astronomers has used the James Webb Space Telescope to identify the first rich population of brown dwarf candidates outside the Milky Way, located in the star cluster NGC 602. This cluster, situated near the Small Magellanic Cloud about 200,000 light-years from Earth, closely resembles conditions in the early Universe, featuring low levels of heavy elements and ongoing star formation.
NGC 602 is characterized by dense dust clouds, ionized gas, and its associated HII region N90, which contains ionized atomic hydrogen. These factors make it an excellent location for studying star formation in an environment different from our solar neighborhood. The team, including researchers Peter Zeidler, Elena Sabbi, Elena Manjavacas, and Antonella Nota, successfully detected candidates for young brown dwarfs in this cluster.
This has never been possible before and will remain impossible from the ground for the foreseeable future.
Brown dwarfs are massive objects, typically between 13 and 75 times the mass of Jupiter. They can be free-floating, not bound to a star like exoplanets. Some share traits with exoplanets, such as atmospheric composition and storm patterns.
Elena Manjavacas, part of the research team, noted that while about 3,000 brown dwarfs have been identified in our galaxy, this discovery marks the first detection of such candidates outside the Milky Way.
Antonella Nota emphasized the synergy of the Hubble and Webb telescopes, stating that while Hubble revealed the presence of young low-mass stars in NGC 602, Webb allowed them to see the significant formation of substellar masses in the cluster.
Peter Zeidler added that their findings support the theory that the mass distribution of objects below the hydrogen burning limit continues the stellar distribution, indicating that brown dwarfs form similarly to stars but do not accumulate enough mass to ignite nuclear fusion.
The team’s data includes a new image from the James Webb Space Telescope’s Near-InfraRed Camera (NIRCam), showcasing the stars in NGC 602, young stellar objects, and the surrounding gas and dust ridges. This image also reveals significant background contamination from galaxies and other stars in the Small Magellanic Cloud, with observations made in April 2023.
Elena Sabbi highlighted that studying these young, metal-poor brown dwarfs brings us closer to understanding star and planet formation in the early Universe’s harsh conditions. Elena Manjavacas emphasized the significance of these discoveries, noting that these are the first substellar objects identified outside the Milky Way, paving the way for future groundbreaking findings.
