Brown Dwarfs Are Seen as Both Failed Stars and Giant Planets

Saturday, 24 March 2018 - 5:08PM
Space
Astronomy
Saturday, 24 March 2018 - 5:08PM
Brown Dwarfs Are Seen as Both Failed Stars and Giant Planets
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NASA/JPL-Caltech
Most of the time, the difference between a star and a planet is pretty clear: a star is a huge ball that burns hydrogen and releases lots of energy and light, while a planet is a much smaller collection of rock or gasses which don't do this.  

But they both fall on a spectrum of "large bodies made up of cosmic materials", and a brown dwarf is an unusual cosmic quirk that falls somewhere in the middle. It doesn't fuse hydrogen, only a similar material known as deuterium, and so it doesn't produce light, even though it has almost the density and size of a real star.

So are they "failed stars" as some astronomers believe, or simply enormous gas giants that could be called "super Jupiters"? Henry Reich, who runs the YouTube channel MinutePhysics, gave a comprehensive rundown on why brown dwarfs have the shaky classification they do, and how accurate either description is.

You can see the full explanation in his video below:



To the brown dwarf's credit, it moves like a star: while planets tend to strictly move in orbit around a star, a brown dwarf can move more independently within star clusters, although it's not uncommon for a brown dwarf to be tagging along with another star to the point where it's basically in orbit anyway. In those situations, the brown dwarf will be several times the mass of any planets in the star's orbit.

And beyond that, there's another important distinction between stars and planets - stars are thought to form from collapsed clouds of cosmic gas and dusts, while planets will typically form out of the leftover materials from the star's creation. Brown dwarfs form the first way, independently without needing scraps from another star.



While there's still debates among astronomy circles over what exactly it is, it appears to be closer to a star, although it's lacking the key qualities of one. A brown dwarf is a body that formed the same way stars do, but failed to collect enough matter that it could grow to a size where it could fuse hydrogen and produce light.

And in that sense, it truly is a "failed star" indeed.
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