Consider an advanced civilization/organism, that has converted all the
planets in the solar system into a Dyson sphere. That's all very well, but
isn't it inconvenient that 99.9% of the mass of the system hasn't been put
to good use? It's just sitting there, being a very inefficient fusion
generator. How can we dismantle it, so we can get it to give up its energy
faster, and extract some useful materials from it? Here's how!
Remember that message I sent out a few weeks ago, about how you could build
a device that could hover indefinitely in the atmosphere of the Sun? Well,
consider this: such devices could be made self-reproducing, so they could
cover much of the area of the Sun, and then used to extract raw materials
from the substance of the Sun. The Sun is currently 75% hydrogen, 24%
helium, and 1% other stuff, mostly carbon, oxygen and nitrogen. The
hydrogen and helium are so abundant as to be valueless, so we leave them.
The heavier elements can be extracted to build more Dyson sphere.
The cool thing is that we can extract from the atmosphere two isotopes that
are both fairly abundant and have what astrophysicists call 'fragile
nuclei', meaning that they are good fuels for fusion reactions. The two
isotopes are helium-3 and nitrogen-15. These are lousy fuels compared to
deuterium and tritium, which is what all fusion bombs and reactors have used
to date, but all the deuterium and tritium in the Sun burned up long ago.
The outer layer of the Sun is swirling around, constantly bringing new
material to the surface. This layer has about 70% of the volume of the Sun,
and 10% of the mass. So the extraction machines at the surface can go on
for a long time before running out of stuff to process. After a few hundred
thousand years, we will have extracted most of the helium-3 and nitrogen-15
in the swirly part of the Sun (the core of the Sun is non-swirly and doesn't
mix with the outside). This will amount to a ball about the size of the
Earth.
This ball is the mother of all fusion bombs. Unfortunately, unlike the
regular kind, it burns relatively slowly. It needs something to hold it
together while it burns up. I spent a long time designing impractical
systems of crashing planets and self-imploding bombs before I realized that
there is one place in the Solar system where there is enough pressure to
hold the bomb together while it burns: the center of the Sun. And the heat
of the Sun can provide a handy ignition source.
One of the problems with using the Sun for heat and pressure is that it is
very springy: any increase in fusion rate at the center will increase the
pressure, which will cause the Sun to expand, which will cool the gas,
causing the heat production to slow. You can get around this by mixing some
lead with the fusion fuel, forming degenerate matter, which does not expand
when the temperature increases, and is also a good insulator at these
temperatures, so the heat will tend to stay confined in the bomb until
burning is complete.
How to get the bomb to the center of the Sun? I suggest wrapping it in a
few thousand miles of inert, abundant stuff (say aluminum and silicon) and
then just dropping the whole ball in. The Sun is, after all, gas all the
way down, and much less dense than the bomb, so according to my calculations
the bomb should fall to the core in about half an hour. Just how much of
the outer layers gets stippped off by air resistance on the way is hard to
know; such calculations are at the cutting edge of present-day astrophysics.
So, having dropped the bomb to the center of the Sun, we wait for it to go
off. For several weeks, fusion proceeds at a relativly sedate pace, as the
bomb slowly gets hotter and hotter. The hotter it gets, the faster it
burns, etc, until it finally burns most of its mass in a tiny fraction of a
second. This heats the lead enough to un-degeneratize it, this lets it
expand, and the entire Sun is given a mighty kick in the butt (well, the
core, but you get the idea).
The shock wave propagates out to the surface and either blows off a few
percent of the mass of the Sun or merely inflates the Sun to twice normal
size for a few hundred thousand years. But wait, you say, that's all? I
thought you were going to actually blow up the entire Sun! Well, don't
worry, that's the next step.
Remember how ony the outer 10% of the Sun's mass was accesible from the
surface? Well, now that the deep interior has been mightily heated,
convection will make the entire depth of the Sun swirly, and all of it will
eventually come to the surface. 99% of the Sun's helium-3 was down below
the layer we could reach before. Now it will be brought up to the surface,
where we can build the grandmother of all fusion bombs with it. This one is
about the size of Uranus. We drop that in, wait a few weeks, and KABOOM!
The Sun is history.
>From the resulting gas cloud, we build lots of Jupiter Brains and all live
happily ever after until the Big Crunch. But that's another story...
--CarlF
PS. What's the reliability of this scheme? Well, I read a few books on the
topic of thermonuclear astrophysics, the Sun and stellar interiors. The
fusion rate calculations I'm pretty confident of, the degenerate matter
stuff is so-so, and the air resistance calculation is an extrapolation from
the current behavior of the Sun, which amounts to a wild guess. I'm
confident that the Sun contains enough fusion fuel to blow it to
smithereens, so the problem is simply one of releasing the energy fast
enough and in the right place.