The border between what is a star and what is a planet is blurry, and new findings from the James Webb Space Telescope (JWST) have made it even less clear. These objects appear to be brown dwarfs, commonly referred to as failed stars, but they are closer in size to giant planets 鈥� they may be the smallest stars ever spotted.
at the Pennsylvania State University and his colleagues spotted these three bodies in a star-forming cluster called IC 348, which is about 1000 light years away. The smallest of them has an estimated mass of three to four times the mass of Jupiter, smaller than any other star astronomers have found.
While they do not tend to have nuclear fusion at their cores, brown dwarfs are often considered stars instead of planets because of the way that they are born. While planets form from discs of debris around young stars, brown dwarfs and regular stars form when clouds of gas collapse under their own gravity. Given their small sizes, it is possible that these newfound objects are actually free-floating rogue planets and not stars, but their environment in IC 348 makes that unlikely.
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鈥淚n theory, it鈥檚 possible that planets are ejected from their star systems 鈥� in fact, we think it鈥檚 almost guaranteed to happen at some level,鈥� says Luhman. 鈥淏ut the cluster that we鈥檙e looking at is quite young 鈥� it鈥檚 only about 5 million years old 鈥� so it seems unlikely that there鈥檚 been enough time for giant planets to form and then to get thrown out of their star systems for us to find them free-floating.鈥� On the other hand, these objects might not be massive enough to have collapsed under their own gravity, so it is nearly as tough to explain them as brown dwarfs.
The researchers also found an anomaly in the atmospheres of two of these worlds: molecules of a complex hydrocarbon that has never been seen beyond our solar system before. Theoretical models of brown dwarf atmospheres do predict hydrocarbons, but mostly methane, which is relatively simple 鈥� nothing as complex as these unidentified molecules.
鈥淚t鈥檚 a very big mystery. It鈥檚 pretty rare that we encounter a molecular species like this that is just totally unexpected and it is abundant,鈥� says Luhman. 鈥淚t鈥檚 unclear why it鈥檚 there, how it鈥檚 forming.鈥�
He says the best way to figure out how the hydrocarbons got into these objects, as well as distinguishing whether they are really brown dwarfs or simply rogue planets, is to hunt for more of them. When we have spotted more of these borderline objects, we can compare and contrast them with one another to find clues as to which are planets and which are stars.
The Astronomical Journal
