This bizarre object, found about 450 light years away in the constellation Taurus, is slightly too awesome to be a planet but slightly too cool to be a star. What is it?
There is actually quite a bit of debate about that. The object appears to have a ring of debris around it, and to have been created when it collapsed out of rapidly-spinning gas, the way a star is formed. That would make it a brown dwarf. But it's so small and cool that it might be more of a mega-Jupiter. It also has a small brown dwarf companion, which might be its twin, formed from the same materials, or may have formed on its own. Indeed, some astronomers say the object might be part of a quadruple star system. According to Alan Boyle, writing on Cosmic Log:
The observations suggest that the mystery object and its brown-dwarf companion may be part of a quadruple-mini-star system, along with a red star and brown-dwarf companion found in the same celestial neighborhood.
In the end, what all these disagreements reveal is that there's a vast gray area between star and planet. Planetary scientist Alan Sterne told Cosmic Log:
It shows planets form lots of ways, so choosing origin method [as a criterion] is a poor way to go. Sort of like saying a human has to be made by both parents, except a human can be made in a test tube, or by cell division (identical twins). A planet should be defined by its characteristics, not its circumstances of location or origin or anything else. When you pull up to one, you know it's a planet or it is not. Why is this hard for some? Why do some want to make something hard out of something so easy? (And yes, that's a rhetorical question.)
via Cosmic Log