From: m.driussi@genie.geis.com
Subject: (urth) slow black hole
Date: Sun,  5 Jul 98 19:55:00 GMT

prion,

You saw-bird, you: a slow black hole could be used to "stellificate"
a jovian world like Jupiter.

Secretly we'll call this the "2010: Odyssey Two" scenario, but in public
we reference Martyn J. Fogg's TERRAFORMING (1995) and the notes therein
from his 1989 paper, "Stellifying Jupiter: A First Step to Terraforming
the Galilean Satellites," published in JBIS.

"Identifying three principal assumptions crucial to its feasibility:

"1. Primordial black holes exist, are detectable and occur in a range
of masses in the Solar System.

"2. It will become possible to maneuver low-mass black holes and embed
them within planets.

"3. Accretion onto the hole occurs at the Eddington limit, with a
relatively high rest mass to energy conversion efficiency in the
infalling material.

"I examined all three of these assumptions in detail in my original
paper.  Suffice it to say here that it is thought possible that
primordial black holes, of a wide range of masses, could have been
formed in the Big Bang.  None have yet been detected and so their
existence has yet to be proved, or non-existence disproved.  Although
the smallest of them (up to an initial mass of ~10^12 kg) would have
evaporated by now due to the emission of Hawking radiation, holes
useful for the purpose of stellification would be about a million
times more massive than this and would have undergone very little
change since the origin of the universe . . . .

"Assumption 3 is particularly important, as the hole must not eat up
the planet it has stellified too quickly and should convert as much
of the accreted mass as possible into energy that escapes in the form
of radiation.  The Eddington limit applies when the accretion rate is
very great.  The luminosity produced by the accretion process exerts
a pressure on the infalling plasma and tends to retard the flow.  The
photon force acts almost entirely on electrons but gravity works
equally well on electrons and protons.  Hence electrons move outward
in relation to protons creating and electric field that trasfers the
photon force from electrons to protons.  The luminosity ultimately
approaches a critical value known as the Eddington limit:

"L<edd> = {4(Pi)(G)(M<H>)(m<p>)(c)}/sigma<es> ~ 6.35 (M<H>)

where M<H> is the mass of the hole, m<p> is the proton mass, and
sigma<es> is the total electron scattering cross-section (6.57 x
10^-29 m^2).  When the accretion luminosity rises above L<edd>, the
radiation pressure becomes large enough to prevent any further
inflow.  Accretion is thus self-regulated" (TERRAFORMING, p. 463).

[mantis note: I'm using "< >" brackets to denote subscript.]

"Potentially therefore, a small black hole could provide a power
source for the interior of a stellified planet such as Jupiter that
operates more efficiently than the processes in the core of the Sun.
It is emphasized, however, that the accretion process is still
clouded by a great deal of uncertainty, especially where accretion
onto microscopic black holes is concerned.  It is possible that the
radiation released by accretion from such a dense medium as the
interior of a planet may itself be swallowed by the hole, as the
diffusive velocity of the radiation relativeto the matter may be
exceeded by the matter's infall velocity.  In this extreme case,
accretion is unimpeded by any `back reaction' and calculations
suggest that Jupiter would vanish =in less than a human lifetime=!"
(TERRAFORMING, p. 464).

[mantis note: gratuitous italics at the very end is my own
addition. "Less than a human lifetime" is assumed to mean something
greater than "less than a mayfly's lifetime"; human lifetime having
an outer edge of what, 70 or 100 years.]

Interesting enough, in the section on "Asteroengineering," which
involves modifying our sun to avoid the disasterous red-giant phase,
the focus is on papers (1990 and 1993) by Martin Beech, looking at
five techniques, including my favorite "Accretion onto a central
black hole" with the application "Luminosity determined by
controlled accretion onto a small black hole at the stellar core"
(TERRAFORMING, p. 458).

These starry-eyed engineers!  Where =do= they get their fantastical
ideas?!

=mantis=

*More Wolfe info & archive of this list at http://www.urth.net/urth/