# Re: Dyson spheres are not dark

Anders Sandberg (nv91-asa@nada.kth.se)
Thu, 26 Jun 1997 10:56:55 +0200 (MET DST)

On Wed, 25 Jun 1997, Dejan Vucinic wrote:

> o What is the minimal distance from Sun at which a (diamondoid?)
> statite can preserve its crystalline structure? Is melting
> point or radiation damage the limiting factor? (In case of a
> red giant it might be possible to sail inside the star for a
> while.)

Hmm, diamond can probably stand around 4000K, although nanodevices
likely break down at 1000K (judging from the NASA simulations). The
temperature of a blackbody sphere is T=(E/(4 pi r^2 sigma))^1/4
where E is the energy output of the sun, r is the radius and sigma
the constant of the the Stefan-Boltzman's law.

Putting 4000K into the equation, we get 1.48e9 meters, or around 1.4
million kilometers. For 1000K we get a radius of 2.37e10 meters, or
around 23 million kilometers. This is roughly 2 and 32 solar radii
respectively.

> o Outgoing radiation doesn't have to have a blackbody spectrum.
> Lasing comes to mind, or one could heat up relatively small
> radiators to a very high temperature.

The laser idea probably won't work thermodynamically, you must get
rid of entropy, not just energy.

> o As a matter of fact, outgoing radiation doesn't have to be
> radiation at all, what about gas cooling? A statite close to
> the star could cool itself by accelerating gas from the corona,
> eating away its host.

Sounds possible in principle, but I think the corona is too thin to
be a good coolant.

> --d(isn't physics fun when you don't have to give answers)v

I couldn't agree more!

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