Astronomers using the NASA/ESA/CSA James Webb Space Telescope have detected a population of 64 brown dwarf candidates with masses ranging from 50 to 84 Jupiter masses in the star cluster NGC 602.
This image of NGC 602 includes data from Webb’s NIRCam (Near-InfraRed Camera) and MIRI (Mid-InfraRed Instrument) instruments. Image credit: NASA / ESA / CSA / Webb / P. Zeidler / E. Sabbi / A. Nota / M. Zamani, ESA & Webb.
NGC 602 is a very young, with an age of 2-3 million years, star cluster approximately 200,000 light-years in the constellation of Hydrus.
Otherwise known as ESO 29-43, it resides in the wing of the Small Magellanic Cloud.
The local environment of NGC 602 is a close analogue of what existed in the early Universe, with very low abundances of elements heavier than hydrogen and helium.
The existence of dark clouds of dense dust and the fact that the cluster is rich in ionized gas also suggest the presence of ongoing star formation processes.
Together with its associated HII region N90, which contains clouds of ionized atomic hydrogen, this cluster provides a valuable opportunity to examine star formation scenarios under dramatically different conditions from those in the solar neighborhood.
Using Webb, Dr. Peter Zeidler from AURA and ESA and his colleagues were able to detect 64 brown dwarf candidates in NGC 602 — the first rich population of brown dwarfs outside our Milky Way Galaxy.
“Only with the incredible sensitivity and spatial resolution in the correct wavelength regime is it possible to detect these objects at such great distances,” Dr. Zeidler said.
“This has never been possible before and also will remain impossible from the ground for the foreseeable future.”
“Until now, we’ve known of about 3,000 brown dwarfs, but they all live inside our own Galaxy,” said Dr. Elena Manjavacas, also from AURA and ESA.
“This discovery highlights the power of using both Hubble and Webb to study young stellar clusters,” said Dr. Antonella Nota, executive director of the International Space Science Institute.
“Hubble showed that NGC 602 harbors very young low mass stars, but only with Webb we can finally see the extent and the significance of the substellar mass formation in this cluster. Hubble and Webb are an amazingly powerful telescope duo!”
“Our results fit very well with the theory that the mass distribution of bodies below the hydrogen burning limit is simply a continuation of the stellar distribution,” Dr. Zeidler said.
“It seems they form in the same way, they just don’t accrete enough mass to become a fully fledged star.”
“By studying the young metal-poor brown dwarfs newly discovered in NGC 602, we are getting closer to unlocking the secrets of how stars and planets formed in the harsh conditions of the early Universe,” said Dr. Elena Sabbi, an astronomer at NSF’s NOIRLab, the University of Arizona, and the Space Telescope Science Institute.
“These are the first substellar objects outside the Milky Way” Dr. Manjavacas said.
“We need to be ready for new ground-breaking discoveries in these new objects.”
The results appear in the Astrophysical Journal.
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Peter Zeidler et al. 2024. Discovering Subsolar Metallicity Brown Dwarf Candidates in the Small Magellanic Cloud. ApJ 975, 18; doi: 10.3847/1538-4357/ad779e
