It’s been known for a while now that there’s no clear boundary between a very large planet and a very small star. 1995 saw the discovery of the curious brown dwarf stars. Stellar inbetweeners, too small to be true stars but too massive to be true planets. This caused much contention amongst star formation theorists, because no one could say for certain whether brown dwarfs form like stars or planets.
This image could, perhaps, solve that mystery. Taken by Spitzer using infrared, this is a stellar cocoon, nestled deep within the Taurus-Auriga dark cloud complex. A dense knot of gas and dust in a vast interstellar cloud. These cocoons are where stars gestate, and this one contains a pair of twins. Brown dwarf twins.
Admittedly, they still need to confirm that this pair are indeed brown dwarfs, but they’re the best candidates so far. In fact, they don’t yet know very much about these two. Are they fully condensed yet? Might they have the potential to form planets? They just don’t know. What they do know is that this seems to answer that question of their formation mechanism. These are brown dwarfs which are clearly forming the way stars do.
Personally though, I wouldn’t be too surprised if brown dwarfs could actually form via either mechanism. We still haven’t been able to actually observe planets forming around stars. Just considering the statistics, I wouldn’t be surprised if every once in a while, a planet was formed with enough mass to burn deuterium and become a brown dwarf.
Source: Spitzer Press Release