I believe I had commented previously in the list on the possible
presence of a "Brown dwarf desert" between lower mass brown
dwarfs and heavier planets.
This situation is clarified on "The Discovery of Brown Dwarfs"
by Gibor Basri in the April Scientific American.
URL: http://www.sciam.com/2000/0400issue/0400basri.html
There is a paucity of brown dwarfs in the studies searching
solar mass stars for planets that have lead to the discovery of many
putative super-Jovian massed planets. This is apparently because the
typical range of masses between binary stars seems to be about an order
of magnitude. Stars of 0.1 solar mass are going to be red dwarfs
and not brown dwarfs. Brown dwarfs are being found as binary companions
of lower mass stars (e.g. red dwarfs). This is presumably because the
mass of the stars depends on the gas cloud density and the difficulty in
setting up cloud conditions that would lead to binaries where
one star is very large and its partner is very small. Brown
dwarfs are also being found as single stars, though it is not
clear whether these may be due to low gas cloud densities or
slingshot events similar to those that lead to rogue planet formation.
Interestingly the quantities of stars and brown dwarfs in clouds
like the Pleiades are similar, and if extrapolated to the galaxy
would argue for the presence of 100 billion brown dwarfs.
Unless star lifting to the point of turning off thermonuclear fusion
is easy, there should be an argument that SIs colonize and restructure
brown dwarfs before they colonize and restructure red dwarfs. So as
the population surveys (DENIS, 2MASS, Sloan DSS, etc.) come in if
there is a deviation in the estimates of the Initial Mass Function
(star formation theory) and the observed red dwarf/brown dwarf
abundances, that would argue that SIs are siphoning off the brown
dwarf population.
So, the strategic development of galaxies may be:
(a) Colonize the brown dwarfs because they aren't good for much else.
(They actually represent galactic hazards in the long term because
to a lesser extent than rogue planets, it is difficult to see them
approaching at a distance). To minimize long term collision avoidance
costs, you want to turn them into something useful and put that
material into well-defined, stable galactic orbits. The development
of brown dwarfs may allow better energy utilization since the
nuclear fuel can be burned at a controlled rate (in thermonuclear
reactors), dictated by computational requirements, rather
than an uncontrolled rate dictated by the mass of the star.
(b) Let the stars burn away, since they constitute efficient breeder
reactors for heavy metals (C, Ti, W, etc.) that you need for specific
construction purposes.
The failure to colonize the galaxy completely, argues that
(a) intelligent technological life is very difficult; and/or
(b) diversity desirability or morality function(s) come into play; and/or
(c) the diminishing computational returns of widely distributed
computronium supporting advanced "civilizations" make endless
expansion pointless.
Its probably worth noting that it is going to take dozens of brown
dwarfs to construct objects of the masses observed in the gravitational
microlensing results (~0.3-0.5 M_sun), so the assembly of these
objects may require many millions of years if you want to minimize
the energy/mass wasting orbital delta-V adjustments.
Robert
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