The James Webb Space Telescope (JWST) has identified what may be the first brown dwarfs—or “failed stars”—ever detected beyond the Milky Way.
These objects, located in the Small Magellanic Cloud (SMC) at a distance of about 200,000 light-years, were found in the young star cluster NGC 602. The discovery, made possible by JWST’s advanced infrared capabilities, offers a glimpse into star formation in environments resembling the early universe, making this find a significant milestone in our understanding of stellar evolution.
Brown dwarfs beyond our galaxy
Brown dwarfs are distinct objects that sit on the boundary between stars and planets, with masses too low to sustain nuclear fusion yet high enough to be distinguished from gas giants. To date, around 3,000 brown dwarfs have been identified within the Milky Way, but detecting them in other galaxies has remained an enormous challenge due to their faintness. The JWST, with its Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI), penetrated dense interstellar dust clouds in NGC 602 to reveal faint objects consistent with brown dwarf characteristics. Peter Zeidler of the European Space Agency (ESA) described JWST’s achievement, stating, “Only with the incredible sensitivity and spatial resolution in the correct wavelength regime is it possible to detect these objects at such great distances.” This achievement is unlikely to be replicated from Earth-based telescopes, solidifying JWST’s role in probing these elusive substellar objects.
The JWST’s findings were enhanced by the Hubble Space Telescope’s past observations, which identified NGC 602 as a particularly active cluster with many young, low-mass stars. By revisiting the cluster with JWST’s greater sensitivity, researchers could study brown dwarf candidates individually. Antonella Nota from the International Space Science Institute emphasized, “Hubble showed that NGC 602 harbors very young low-mass stars, but only with the JWST, can we finally see the extent and the significance of the substellar mass formation in this cluster.”
The Importance of Brown Dwarf Formation in a Metal-poor Environment
The SMC provides a unique window into conditions that mirror those of early galaxies. This dwarf galaxy has relatively few heavy elements, also known as “metals,” which are critical in traditional star formation. Elena Sabbi, a researcher at the University of Arizona, explains, “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.” Brown dwarfs in these regions are more likely to exhibit behaviors and properties similar to those seen in the earliest stellar generations, offering a proxy for examining the processes that shaped the young universe.
JWST’s findings support the theory that brown dwarfs, like stars, form through the gravitational collapse of gas clouds but fail to acquire sufficient mass to ignite. This discovery thus broadens our understanding of stellar formation and suggests that brown dwarfs naturally occur across a variety of star-forming environments. In confirming that brown dwarfs populate metal-poor regions, the discovery opens new questions about the frequency and formation processes of these substellar objects across different galactic conditions.
Implications for Future Research with JWST
This pioneering discovery showcases JWST’s unparalleled ability to illuminate areas beyond the reach of other telescopes, both in terms of sensitivity and resolution. With its capacity to peer through thick dust clouds, JWST is uniquely equipped to study environments like the SMC’s NGC 602 and potentially other nearby dwarf galaxies. The discovery provides a new framework for studying star-forming regions and the distribution of substellar objects outside our galaxy, expanding our understanding of cosmic history and star formation across different types of galaxies.
With its sensitivity, JWST will allow astronomers to examine structures and characteristics of early stars, brown dwarfs, and even planets with unprecedented detail. As Zeidler notes, “This has never been possible before and also will remain impossible from the ground for the foreseeable future.” This finding is the first of what astronomers expect to be many groundbreaking observations from JWST, illuminating the frontier of stellar formation beyond the Milky Way.
