Brown dwarfs are considered the missing link between stars and giant planets. They are too small and cool to be stars, but they are usually larger and hotter than planets.
However, with there being more brown dwarfs than there are stars like our Sun, they end up being an incredibly diverse bunch. Their temperatures can range from as hot as a star to as cool as a planet, while their ages and composition can vary drastically too.
To find out what was driving these differences, an international team led by the Carnegie Institution for Science's Jacqueline Faherty, looked at the age, chemical composition, and size of a large sample of brown dwarfs and found that the atmospheric conditions of these objects played a major role in why they look different.
In a paper, published by The Astrophysical Journal Supplement Series, the team studied 152 objects that were believed to be young brown dwarfs, and confirmed either their origin or their age, or both. From this, the team was able to create a sample of objects that was independent of age and chemical composition. This allowed them to work out that it was the atmospheric conditions – the cloud composition, structure, and weather phenomena – that was driving the changes in the brown dwarfs. And studying these objects could reveal new insights into exoplanets, too.
"I consider these young brown dwarfs to be siblings of giant exoplanets. As close family members, we can use them to investigate how the planetary aging process works," Faherty said in a statement. “Brown dwarfs are far easier to study than planets because they aren’t overwhelmed by the brightness of a host star.”
Brown dwarfs are essentially failed stars. They are the smallest objects that form like a star, but they lack the mass to start nuclear fusion at their core, and after a hot beginning they cool down and shrink. The data we can obtain from them can also be used as stand-ins for exoplanets. All the brown dwarfs in this study formed in regions that also form exoplanets, and brown dwarfs are actually easier to study with current technology.
Future telescopes, like the James Webb Space Telescope, will allow better observations of both brown dwarfs and exoplanets, so we’ll hopefully soon learn more about these objects outside the Solar System.