Brown Dwarfs: “Over-Achieving Jupiters” not “Failed Stars”

Why is the term “failed star” synonymous with brown dwarfs? On the one hand, brown dwarfs lack the mass to sustain nuclear fusion in their cores. On the other hand, who said brown dwarfs were trying to be stars? Who ever said that becoming a star was the pinnacle of stellar living? Perhaps brown dwarfs are perfectly happy the way they are. In a world of equality and political correctness, brown dwarfs could be viewed as “over-achieving Jupiters”, or gas supergiants…

Brown dwarfs are often considered to be the bridge between planets and stars, they are too massive to be considered to be a planet (as they have convective interiors with no layered differentiation of chemicals with depth), and yet they are too small to be a star (they cannot fuse hydrogen in their cores, although some brown dwarf classes may fuse lithium and deuterium). That said, brown dwarfs do occupy the lower right-hand corner of the Hertzsprung-Russell diagram, so they are still classified in stellar terms. Although “brown dwarf star” is probably a little too generous.

Brown dwarfs are also technically not “brown”, they are a kind of dirty orange (with a hexadecimal colour of #EB4B25) as astronomers don’t recognize brown as a colour.

So “brown” dwarfs aren’t really brown and they are suffering an identity crisis between being a star and a planet. In fact, before brown dwarfs became brown dwarfs, there were suggestions to call these strange planetary/stellar bodies substars or planetars (can you sense the confusion?).

Compared with our Sun, brown dwarfs are pretty small (0.01-0.08 Solar masses) but compared with a gas giant such as Jupiter, they are huge (13-80 Jupiter masses). However, brown dwarfs don’t expand much larger than the radius of Jupiter (making it hard to distinguish between a brown dwarf and a gas giant exoplanet).

Therefore, why don’t we be a little more “glass half-full” when describing brown dwarfs. Although brown dwarfs undoubtedly have star-like qualities, they have strong planet-like qualities too. So in the traditional superlative descriptions of some astronomical objects (i.e. supermassive black hole), why not emphasise the brown dwarf’s strong planetary points. Rather than “brown dwarf”, what about “gas supergiant” and rather than “failed star”, why not “over-achieving Jupiter”?

Just a thought.

Special thanks to Adam Zuckerman for the entertaining conversation we had when discussing the pros and cons of Are Brown Dwarfs More Common Than We Thought?