The James Webb Space Telescope (JWST) has identified the smallest known brown dwarfs, often called "failed stars," in the star cluster IC 348, located about 1,000 light-years away in the Perseus star-forming region. These objects, discovered in a survey led by astronomer Kevin Luhman of Pennsylvania State University, include a record-breaking brown dwarf with a mass of just three to four times that of Jupiter, making it the least massive free-floating brown dwarf observed to date. Two other brown dwarfs were also found, with masses up to eight times that of Jupiter.
Here's a breakdown of the key findings:
- Smallest Brown Dwarfs Discovered: Astronomers, led by Kevin Luhman of Pennsylvania State University, found a batch of nine new brown dwarfs, including two that are the smallest examples ever seen. These two smallest brown dwarfs have masses around twice the mass of Jupiter, radically widening the previously understood mass scale for brown dwarfs. Previous estimates placed the lower limit between 13 to 60 times the mass of Jupiter.
- "Failed Stars" Definition: Brown dwarfs are often called "failed stars" because they form from collapsing clouds of gas and dust, similar to stars, but they don't gather enough mass to ignite the sustained nuclear fusion of hydrogen into helium in their cores. This hydrogen fusion is the defining process of a main sequence star. While they do undergo some forms of nuclear fusion (like deuterium fusion), it's not enough to classify them as true stars.
- Location of Discovery: The team found these small brown dwarfs lurking among young stars in IC 348, a star-forming cluster in the Perseus Molecular Cloud, approximately 1,000 light-years from Earth.
- Challenging Formation Theories: The discovery of such low-mass brown dwarfs challenges existing theories of star formation. It was previously thought that the process that makes stars would not be able to produce objects down to only twice the mass of Jupiter, which is 500 times smaller in mass than the Sun.
- Unidentified Hydrocarbon: A surprising find was the presence of signals from an unidentified hydrocarbon (a chemical compound composed solely of hydrogen and carbon atoms) in the atmospheres of these new brown dwarfs. Its origin is a mystery, and its presence has led to the proposal of a new spectral class (H) defined by this species.
- Implications: This discovery helps to better define the mass dividing line between large planets and small brown dwarfs, and also between large brown dwarfs and small stars. Studying these objects also provides crucial insights into the star formation process and potentially the conditions in the early universe.
- JWST's Role: The James Webb Space Telescope's exceptional infrared sensitivity and sharp vision were crucial for detecting these faint, cool objects, which would be difficult or impossible to observe with other telescopes. The JWST's capabilities allow astronomers to peer through dense dust and gas, which is essential for studying these young, newly formed objects.