Reviewed by Lexie CornerOct 24 2024
An international team of astronomers has discovered the first brown dwarf candidates outside the Milky Way in the star cluster NGC 602 using the NASA/ESA/CSA James Webb Space Telescope. This research was published in The Astrophysical Journal.
A star cluster is shown inside a large nebula of many-colored gas and dust. The material forms dark ridges and peaks of gas and dust surrounding the cluster, lit on the inner side, while layers of diffuse, translucent clouds blanket over them. Around and within the gas, a huge number of distant galaxies can be seen, some quite large, as well as a few very large and bright stars nearer to us. Image Credit: ESA/Webb, NASA & CSA, P. Zeidler, E. Sabbi, A. Nota, M. Zamani (ESA/Webb)
NGC 602, a young star cluster, resides in the outer reaches of the Small Magellanic Cloud, a satellite galaxy of the Milky Way, approximately 200,000 light-years from Earth. This region has low abundances of elements heavier than hydrogen and helium, making its environment similar to conditions in the early Universe.
The presence of dark clouds of dense dust and abundant ionized gas suggests active star formation. NGC 602, along with its associated HII region N90, which contains clouds of ionized atomic hydrogen, offers a unique opportunity to study star formation in conditions vastly different from those in the solar neighborhood.
Only thanks to the incredible sensitivity and resolution in the right wavelength range we are able to detect these objects at such great distances. This has never been possible before and also will remain impossible with telescopes on the ground for the foreseeable future.
Peter Zeidler, Study Shared Lead Author, European Space Agency
Brown dwarfs, the more massive cousins of giant gas planets, typically have masses ranging from about 13 to 75 times that of Jupiter, though some can be smaller. Unlike exoplanets, brown dwarfs are free-floating and not gravitationally bound to a star. However, they share certain characteristics with exoplanets, such as storm patterns and atmospheric composition.
Until now, we’ve known of about 3000 brown dwarfs, but they all live inside our own galaxy.
Elena Manjavacas, Team Member, European Space Agency
Team member Antonella Nota, executive director of the International Space Science Institute in Switzerland and the previous Webb Project Scientist for ESA, stated, “This discovery highlights the power of using both Hubble and Webb to study young stellar clusters. Hubble showed that NGC602 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!”
Zeidler added, “Brown dwarfs seem to form in the same way as stars; they just don’t capture enough mass to become a fully-fledged star. Our results fit well with this theory.”
One of the team's data sets includes a new image of NGC 602 captured by Webb's Near-InfraRed Camera (NIRCam) in April 2023. This image reveals the surrounding gas and dust ridges, the cluster’s stars, and young stellar objects. Additionally, numerous background galaxies and other stars within the Small Magellanic Cloud are visible.
Elena added, “These are the first giant exoplanet analogues outside the Milky Way. e need to be ready for ground-breaking discoveries in these new objects!”
These findings were made as part of the JWST GO program #2662 (PI: P. Zeidler). The results were published in The Astrophysical Journal.