Unveiling the Smallest Stars
By Darrell Lee
In a new study, astronomers Kevin Luhman, from the Department of Astronomy and Astrophysics at the Pennsylvania State University, and Catarina Alves de Oliveira, from the European Space Agency, used the James Webb Space Telescope (JWST) to push the boundaries of our understanding of star formation, discovering some of the smallest free-floating "failed stars" ever seen and identifying a mysterious new class of celestial object. While the technology is revolutionary, the nature of these discoveries—finding new categories of objects, detecting unexpected chemistries, and expanding our cosmic catalog—places this work within a long and noble tradition of astronomical exploration. The research provides new insights into how small an object can be as it forms like a star, a question that has been asked in different forms for centuries.
Scientists pointed the infrared eyes of JWST toward a nearby young star cluster named IC 348. Star clusters like this serve as cosmic nurseries, making them ideal places to find newborn, low-mass objects that are still relatively warm and bright from their formation. The team's search successfully identified 39 new brown dwarf candidates, objects more massive than planets but not massive enough to ignite the nuclear fusion that makes stars shine. Spectroscopic analysis confirmed nine of these as cluster members, with the faintest having masses of just 2 to 3 times the mass of Jupiter.
This discovery of ever-smaller free-floating objects is a modern chapter in a very old story. For much of history, astronomers could only study stars. In the 20th century, the discovery of white dwarfs—the incredibly dense, burnt-out cores of dead stars—introduced a new category of celestial object whose existence challenged physical understanding until the development of quantum mechanics. Similarly, the confirmation of the first brown dwarfs in 1995 (like Gliese 229B and Teide 1) filled the long-sought-after gap between the largest gas giants and the smallest hydrogen-fusing stars. Luhman's work with JWST represents the next step on this ladder, pushing down to the very lowest mass limit of objects that can form through this star-like process.
The most surprising discovery, however, was an unexpected chemical signature in the atmospheres of many of these new objects. Eleven brown dwarfs in the cluster showed clear signs of an unidentified hydrocarbon molecule. This was unexpected because existing atmospheric models for such cool objects predict carbon should be locked up in methane.
Faced with a new type of object that doesn't fit existing categories, the researchers propose creating a new spectral class: the "H" class (for hydrocarbon). It follows directly in the footsteps of Annie Jump Cannon and the "Harvard Computers" who, at the turn of the 20th century, created the O-B-A-F-G-K-M stellar classification system that astronomers still use today. Just as astronomers later added the L, T, and Y classes to accommodate the discovery of cooler brown dwarfs, the proposed H class represents the necessary expansion of our cosmic catalog to make sense of JWST's new findings.
Finally, the study found that two of the newly discovered brown dwarfs have circumstellar disks of gas and dust—the raw material for planets. That finding revealed a "hot Jupiter" and proved planetary systems could be wildly different from our own. Luhman's work extends this idea to the lowest rungs of the mass ladder, raising new questions about the diversity of planetary systems in the universe. In summary, this research uses the unprecedented power of JWST not only to find some of the lowest-mass free-floating objects ever observed but also to continue the historical cycle of discovery: finding new populations of objects, encountering unexpected phenomena that challenge our models, and expanding our classification systems to make sense of a more complex and wonderful universe.
Darrell Lee is the founder and editor of The Long Views, he has written two science fiction novels exploring themes of technological influence, science and religion, historical patterns, and the future of society. His essays draw on these long-standing interests and apply a similar analytical lens to politics, literature, artistic, societal, and historical events. He splits his time between rural east Texas and Florida’s west coast, where he spends his days performing variable star photometry, dabbling in astrophotography, thinking, napping, scuba diving, fishing, and writing, not necessarily in that order.