[Traveller_TNE] Re: The Gas Giant in the Habitable Zone Thread

--- In , "DED" <dedly@...> wrote:
>
> Hence why I wrote: "I make no guarantees of the veracity of this
formula (or my math). I'm just passing along the info." =)

Yep. I was just clarifying why the formula wasn't very useful, is all :).

> One question with regards to: "when they start getting more massive
than Jupiter they just compact all the extra mass in the same volume... "
>
> How do we know this? Is it with computer models?

Yeah, with physics really. Once you start adding more mass, it
compacts the stuff in the middle more because the pressure is going up
in the central parts. So instead of increasing the radius, you end up
increasing the density of the planet. A massive brown dwarf packs up
to 60-70 Jupiter masses in a volume that's actually *smaller* than
Jupiter , so its density (and surface gravity) are ridiculously high.
If it crosses the BD/star boundary though then the fusion reactions in
the core make the object expand considerably (to about 200k-300k km
radius) and the density and gravity drop accordingly because of the
extra volume.

I don't think the densities inside brown dwarfs are anywhere near high
enough to form degenerate matter in their interiors - that does happen
in red giant stars, though. In BDs it's just normal gravitational
compaction of matter.