On Wed, Apr 16, 2014 at 04:26:08PM -0700, Asher Royce Yaffee wrote:
> In the rest of the subsector, would the nebula fill up a big chunk
> of the night sky, and be like in the astronomy photos?  Would it
> have a few really young stars with lots of small, wildly unstable
> planets in wildly unstable orbits?

That part is up to you.  A supernova remnant nebula a few parsecs
across will be very young, probably no more than a thousand years.  It
may have other stars in it, but not likely associated with the one
that formed the black hole.  I suspect what you want is a diffuse,
star-forming nebula.  The black hole may have formed inside it
(relatively recently), or it may be passing through.

> The creation of a black hole is, I presume, an explosive process.

In many cases *very* explosive: a Type II supernova.  These usually
result in a substantial loss of mass as well as extremely intense
radiation, so any surviving planets probably escape the weaker gravity
of the black hole (compared with the original star).  Some of the
matter from the explosion may condense into planets.  Most will be
ejected from the system at very high speed, but a small fraction won't
*quite* have enough energy to escape.  Although it won't have much
angular momentum, there are processes by which stable (though usually
highly elliptical) orbits can result.  So such a supernova remnant can
have planets.  Even old planets, if it exploded long ago.

Very large stars (40+ solar masses) probably collapse directly into
black holes without an energetic explosion, with virtually the entire
star's matter collapsing into the new event horizon.  If such a star
had planets, they would remain.  The star's life would have been very
short, as such large stars burn extremely fast and bright.  The system
might be very old, if the star collapsed a long time ago.

> How close could the player characters' lab ship get to a black hole?

If it has an active accretion disk, then it won't look very black.
Quite the contrary, it will be extremely bright and hot.  In some
cases it might be brighter than any ordinary star, as well as emitting
an immense flood of xrays.  In such a case the PCs won't be able to
get close at all.

A fairly old and isolated black hole might have a vicinity cold enough
that only tidal forces limit the approach, probably to about twenty
thousand kilometres.  The ship (and its inhabitants) would be under
significant tidal stress, on the order of a 10% of a gee per metre.
So at 20 metres from the centre of the ship, the tidal acceleration
would be about 2 gees.  That force would be outward from the ship's
centre in line with the black hole, and inward for the perpendicular
plane.  The tidal forces across the human body would probably be very
easily felt by the crew even within artificial gravity, and likely to
cause significant nausea.

At this tidal limit the orbital period would be on the order of a few
*seconds*, with orbital speed about 15,000 km/s.  Even Traveller
reactionless ships would take a long time to maneuver in so close,
more than a week to use their thrusters to slowly spiral inward,
dissipating the enormous gravitational energy.  (And more than a week
back out again)

A hyperbolic approach would work, but give only seconds near minimum
distance.  It would also mean that if even a microscopic amount of
matter was orbiting, encountering it would be instantly fatal.
Impacts at ordinary orbital energies are bad enough, but the kinetic
energy at these speeds would be millions of times greater.

> If they flew a probe at the black hole, would the probe be destroyed
> by radiation first, or would tidal forces rip the probe apart first?

Either or neither, depending on how much matter was nearby.  For
example, it could be destroyed by impact with even an invisibly
tenuous accretion disk or some dust mote.  (A 0.01 cm speck of dust
within the tidal limit above could impact with the energy of an
anti-tank weapon)

> What cool effects could I describe to the players, or arrange for
> them to discover, at a black hole?

There are a few general relativistic effects found nowhere else, but
most involve getting too close to the event horizon.

> In the subsector, I also want to have an aged red giant, a really
> old version of our sun.  Let's assume that the 100-diameter jump
> rule applies to the star's original diameter, otherwise it'll be a
> pain.  But does this mean that the lab ship could jump from the red
> giant's surface?

Yes, or perhaps even from within the star.  The outer layers of red
giant stars are extremely sparse.  That said - cooling would be a
serious problem, even far from the star.  Despite being relatively
cool compared with most other stars, the surface temperature is still
a few thousand kelvin.

> How long does it take a star like ours to transition from normal
> size to red giant size.

On the order of a billion years or so.  It steadily increases in size
before stabilizing for another billion or so years as a red giant.

> And how about some silicon-based life?  What would it look like?
> Could it move?  Could it move quickly?

I think it could look like just about anything.  I'd guess that it
would be no more likely to look like "moving rock" than carbon-based
life looks like "moving diamond".

It's much more likely to consist at the microscale of some assemblage
of flexible structures surrounding extremely complex sets of chemical
processes in some solvent or other (possibly water - it's ridiculously
common and has useful properties).  It probably doesn't *have* to, but
it seems a handy pattern for many evolutionary challenges.

Isaac Asimov suggested that the most likely non-carbon substrate for
life might consist of compounds with siloxane bonds, reacting in water
at higher temperature and pressure.  Some of the the more familiar
siloxane compounds on Earth are silicone oils, gels, resins, and
rubbers - though many of those still contain quite a bit of carbon.
As you can see from these examples, such bonds do not imply rigidity
or hardness any more than diamond's rigidity confers the same property
onto all compounds based on carbon-carbon bonds.

- Tim