Celestia Forums

Here is a supramundane shell around a brown dwarf, as described by Paul Birch;



the relatively thin, solid surface is supported by particle beam levitation above the surface of a brown dwarf, and the human population live on the outside in a landscape artificially lit by energy gathered from the object within.

Excess heat is radiated by the reddish radiator stripes.

Er -
since I first wrote about these artificial worlds, a couple of years ago, I have found out that brown dwarfs have surface gravity in excess of 100gee;
how big would the shell have to be to obtain one gee on the surface?

Unfortunately, 50megs does not allow direct links to images for free accounts, so we can't see your picture.

To first approximation, since the shell is well beyond the star's surface, you can treat the star within the shell as a point source, so gravity falls off as 1/r^2, where r is the distance from its center.

F = GMm/r^2
Where F is the force of gravity
G is the gravitational constant
M is the mass of the star
m is the mass of an object (which can be ignored)
r is the distance from the center of the star

1 Gee = F(earth) = GM(earth)/r(earth)^2
so
F(shell)/F(earth) = [ M(star) * r(earth)^2 ] / [ M(earth) * r(shell)^2 ]
so
r(shell) = sqrt [ M(star) * r(earth)^2 /M(earth) ]

I'll let you fill in the numbers

Of course, for large values of r you may have to take into account the mass of the gigantic shell, too.

1/r^2-
of course; the inverse square law...
I think I knew that, in the back of my mind...

So with a brown dwarf 60,000km in radius and 100 gee, you would need to be 600,000km away to get 1 gee...
a big structure, about as big as the Sun... whoo hoo!
Now to find where to get the material to build it.

Generally I'd say extract the material from the dwarf itself; this makes the object smaller and lowers the gravity...

but trying to extract material from an object with a surface gravity of 100 gee would be a daunting task...
I will have to hope for a few Stevensonian type planets as well to dismantle.