a black hole system

For the purpose of a science fiction story I was wondering what a
black-hole 'solar' system would be like for humans.

Suppose we start with a 10-solar-mass BH and a Jupiter-size gas-giant at
8 AU, and put a human settlement of one of its moons.

How would such a system form: Would a gas-giant survive a
black-hole-forming nova; Would a planetary system survive a collision
beteen a normal star and a black-hole; Would a binary system formed with
a black-hole have stable planetary orbits?
Which mechanism is plausible and what sort of system would result?

Given the lack of solar wind and light pressure, gas and particles would
flow inward. Would this be a major hazard of interplanetary travel? The
furthur in you go, the worse the kinetic energy of these impacts. Would
the bombardments make human travel in the inner system impossible? Would
the energy given off by the accretion disk make life unviable anywhere in
the system?

If you wanted to place satellites or asteroids in circular orbits such
that each one experiences double the time-dilation (halved 'speed') of the
next, what orbital radii would work? Could elliptical transfer orbits
between them work without decay or probable impacts?

How close to the black hole would you need to get for tidal effects to be
noticable on the metre scale (say 0.1g difference)?

The event-horizon is where the escape velocity exceeds the speed of light.
However the escape velocity is defined as escaping to an infinite
distance. For someone close to the black hole, light can reach them from
below the 'infinite' horizon. Suppose satellites were positioned such that
the delta-V between adjacent ones was c/2?

We have

0.5*m*(c/2)^2 = GMm/r_1 - GMm/r_2

which becomes

(c*c)/(8GM) + 1/r_2 = 1/r_1

so the reciprocal of the radii are separated by a constant amount, and
the radii can become arbitrarily small. Placing satellites at these radii
allows signals to be relayed past the nominal event horizon. Is this
correct? What would the inner satellites see of the outside world?


Toby

In sci.physics.relativity, Toby Kelsey

wrote
on Thu, 18 Aug 2005 20:22:22 GMT
:
For the purpose of a science fiction story I was wondering what a
black-hole 'solar' system would be like for humans.

Suppose we start with a 10-solar-mass BH and a Jupiter-size gas-giant at
8 AU, and put a human settlement of one of its moons.

Erm...and how precisely does that settlement keep warm?
Black holes do not glow of their own accord, at least,
not at the same rate as stars; they do radiate but their
temperature is lower than the surrounding Universe --
about 2.5-3 Kelvin.

(Unless you're assuming the hole strips gas from the
Jupiter-size planet. My snap judgement suggests the planet
isn't close enough.)

Since you specified settlers, that's another issue that
verges on science fiction, though a RAMA-type spacecraft
(but without drive engine) might be doable, given
sufficient resources; one might contemplate capturing an
asteroid and focusing orbiting sunlight mirrors or some
other such. Of course there's a large number of issues
here, not the least of which is how one gets those mirrors
into orbit, and how fast the rock cools down afterwards.

But that's a sideline for purposes of this thread.


How would such a system form: Would a gas-giant survive a
black-hole-forming nova; Would a planetary system survive a collision
beteen a normal star and a black-hole; Would a binary system formed with
a black-hole have stable planetary orbits?
Which mechanism is plausible and what sort of system would result?

Given the lack of solar wind and light pressure, gas and particles would
flow inward. Would this be a major hazard of interplanetary travel? The
furthur in you go, the worse the kinetic energy of these impacts. Would
the bombardments make human travel in the inner system impossible? Would
the energy given off by the accretion disk make life unviable anywhere in
the system?

What accretion disk? What's feeding it?


If you wanted to place satellites or asteroids in circular orbits such
that each one experiences double the time-dilation (halved 'speed') of the
next, what orbital radii would work? Could elliptical transfer orbits
between them work without decay or probable impacts?

How close to the black hole would you need to get for tidal effects to be
noticable on the metre scale (say 0.1g difference)?

The event-horizon is where the escape velocity exceeds the speed of light.
However the escape velocity is defined as escaping to an infinite
distance. For someone close to the black hole, light can reach them from
below the 'infinite' horizon. Suppose satellites were positioned such that
the delta-V between adjacent ones was c/2?

We have

0.5*m*(c/2)^2 = GMm/r_1 - GMm/r_2

which becomes

(c*c)/(8GM) + 1/r_2 = 1/r_1

so the reciprocal of the radii are separated by a constant amount, and
the radii can become arbitrarily small. Placing satellites at these radii
allows signals to be relayed past the nominal event horizon. Is this
correct? What would the inner satellites see of the outside world?

I for one can't say at this time.



Toby


--
#191,
It's still legal to go .sigless.

Would a gas-giant survive a
black-hole-forming nova;

Would depend on distance but probably not.

Would a planetary system survive a collision
beteen a normal star and a black-hole; Would a binary system formed
with
a black-hole have stable planetary orbits?
Which mechanism is plausible and what sort of system would result?

What do you call a collision. Is it a collision between the star and
the core of the BH. That is to say the star being engulfed. Again
probably not because there would be an enormous release of energy,
certainly comperable to a supernova if not even biger. If you are
taking about a gravitational slingshot, there would (in principle) be
no difference between a Black Hole and any other type of star, the
answer would be yes although the planetary system might fing itself
scattered a bit with some planets orbiting the original star, some the
Black hole and others in interstellar space.

If you wanted to place satellites or asteroids in circular orbits such
that each one experiences double the time-dilation (halved 'speed') of
the
next, what orbital radii would work? Could elliptical transfer orbits
between them work without decay or probable impacts?

For orbits not to decay they must be Newtonian. This is clear when we
look at a radio attenna. A relativistic orbit is the gravitational
analogue. The exact equations are in

http://myweb.tiscali.co.uk/ianandmar...relativity.htm

I can't write equations here. If you look at the Schwartzchild equation
you will find that if you (as a rough and ready calculation) subtract
the radius of the BH from any distance one hass the Newtonian value
(near as no matter). Newtonian orbital dynamics works with a BH the
same as it always does.

How close to the black hole would you need to get for tidal effects to
be
noticable on the metre scale (say 0.1g difference)?

This is very much in the Newtonian region and is about 20,000km. (10
suns)

The event-horizon is where the escape velocity exceeds the speed of
light.
However the escape velocity is defined as escaping to an infinite
distance. For someone close to the black hole, light can reach them
from
below the 'infinite' horizon. Suppose satellites were positioned such
that
the delta-V between adjacent ones was c/2?

They would be aerials and would therefore not last very long.

NO. If you look at the S equation is is not differentiable at the event
horizon, so this is independent of where you place your satellites

Read

http://myweb.tiscali.co.uk/ianandmar...relativity.htm

for the equations. Particularly Scwartzchild.

For the purpose of a science fiction story I was wondering what a
black-hole 'solar' system would be like for humans.

What is your plot? If it is SF an Earth could have been transported
deliberately. A spinning Black Hole is the most efficient energy
converter there is converting 80% of rest mass into energy. A type 3
civilzation would use a BH for energy. Could a charged BH be used to
generate antimatter? Perhaps.

Would a gas-giant survive a
black-hole-forming nova;
I don't think so.

Would a planetary system survive a collision
beteen a normal star and a black-hole;

If the BH went into the body of the star there would be another
explosion probably even bigger than the original supernova. If it was a
slingshot collision a BH would not behave any differently from any
other star. The planetary system would be broken up, some planets. in
elliptical orbits orbiting the original star, others the BH others
going into interstellar space.

Given the lack of solar wind and light pressure, gas and particles
would
flow inward. Would this be a major hazard of interplanetary travel?

No but the plasma round the BH would be. It will emit lethal X and
gamma rays. Still you can solve anything by encasing yourself in
tungsten.

Would
the energy given off by the accretion disk make life unviable anywhere
in
the system?

It could not evolve. A technological civilation would survive and just
possibly flourish. It would have to come from elsewhere. What about
silicon and a matrix? How do you know we orbit a star and not a BH.
(see Sir Martin Rees).

Planetary motion works in just the same way as with any other star
system. Only difference is at Event Horizon of spinning hole
sacrificial systems (matter thrown into hole) will accelerate you to
near light speed. See abnormal galaxies.

How close to the black hole would you need to get for tidal effects to
be
noticable on the metre scale (say 0.1g difference)?

20,000 km. This is well in the Newtonian region. Straight Newtonian
tides.

If you wanted to place satellites or asteroids in circular orbits such
that each one experiences double the time-dilation (halved 'speed') of
the
next, what orbital radii would work? Could elliptical transfer orbits
between them work without decay or probable impacts?

Orbits would not be stable because of gravitational wave radiation.

The event-horizon is where the escape velocity exceeds the speed of
light.
However the escape velocity is defined as escaping to an infinite
distance. For someone close to the black hole, light can reach them
from
below the 'infinite' horizon. Suppose satellites were positioned such
that
the delta-V between adjacent ones was c/2?

Look at S equation in my file. It is undifferentiable

a) At event horizon
b) At center.

Elsewhere it is differentiable. The EH is a piece of undifferentiable
metric.

so the reciprocal of the radii are separated by a constant amount, and
the radii can become arbitrarily small. Placing satellites at these
radii
allows signals to be relayed past the nominal event horizon. Is this
correct? What would the inner satellites see of the outside world?

See above. If they were outside EH all of the outside world with some
time shifting. NO you can never see through the EH no matter where you
were.

As you are wring SF I would like to remind you of Google terms of use.
If you use these ideas to make a lot of money there is a copyright
issue.

In article ,
says...
For the purpose of a science fiction story I was wondering what a
black-hole 'solar' system would be like for humans.

Suppose we start with a 10-solar-mass BH and a Jupiter-size gas-giant at
8 AU, and put a human settlement of one of its moons.

How would such a system form: Would a gas-giant survive a
black-hole-forming nova; Would a planetary system survive a collision
beteen a normal star and a black-hole; Would a binary system formed with
a black-hole have stable planetary orbits?
Which mechanism is plausible and what sort of system would result?

The first extra-solar planet discovered was in orbit around a pulsar. A
pulsar is just a failed blackhole, so yes, a black hole probably could
have a planet. However, the supernova that formed the blackhole would
blast away the atmosphere of any gas-giant and you'd be left with a
core. A core of what? Rock and iron, metallic hydrogen, diamond, I've
heard all of these suggested. It might have some kind of atmosphere,
boiling out of what's left of the surface, but it wouldn't be a gas-
giant anymore.

Moons, I don't see any way one could survive. The change in mass of the
gas-giant alone would tend to throw them off. Not to mention being
evaporated by the heat of the supernova.

What's left after a supernova would be refractory, fused and baked. Not
too many fluffy atoms of hydrogen, nitrogen or carbon left around. If
the supernovae was recent there might be useful amounts of transuranic
elements there on any solid bodies ready to be swept up. Your human
settlement could keep warm with fission reactors.

snip

The event-horizon is where the escape velocity exceeds the speed of light.
However the escape velocity is defined as escaping to an infinite
distance. For someone close to the black hole, light can reach them from
below the 'infinite' horizon. Suppose satellites were positioned such that
the delta-V between adjacent ones was c/2?

We have

0.5*m*(c/2)^2 = GMm/r_1 - GMm/r_2

which becomes

(c*c)/(8GM) + 1/r_2 = 1/r_1

so the reciprocal of the radii are separated by a constant amount, and
the radii can become arbitrarily small. Placing satellites at these radii
allows signals to be relayed past the nominal event horizon. Is this
correct? What would the inner satellites see of the outside world?

The event-horizon is a wall. You can't fool it with relay satellites.
No information comes out. Even if you did the calculus, with an infinite
number satellites, that very last satellite of the infinite series
wouldn't quite be able to push a photon past the event-horizon.

Marc

Toby Kelsey wrote:

For the purpose of a science fiction story I was wondering what a
black-hole 'solar' system would be like for humans.

...

Toby

I don't know if you would be interested in a somewhat similar
system used by another author, but you might have a look at:
Larry Niven's The Integral Trees.
One review is can be found at:
http://www.larryniven.org/reviews/140.htm

There was als a sequal: The Smoke Ring
http://www.larryniven.org/reviews/158.htm

--
Rick

P.S. If you need to email me, you know what to do with the 'spamtrap'.
___________________________
Buzzard, beginning a dive:
"Patience my Tail Feathers!
'I Aim To Misbehave!'
I'm going to kill something."

wrote:
If you wanted to place satellites or asteroids in circular orbits such
that each one experiences double the time-dilation (halved 'speed') of
the
next, what orbital radii would work? Could elliptical transfer orbits
between them work without decay or probable impacts?

Orbits would not be stable because of gravitational wave radiation.

ian, why can't you distinguish what you're quoting from what you're
writing? Stability is arbitrary: Make satellites as uniform ring
wedges that circle the hole, eventually locking into place.

-Aut