Warp <war### [at] tagpovrayorg> wrote:
>   Actually it would work if the black hole was moving towards us. Then
> the spacecraft could go there and rob part of this momentum and get a
> speed boost back towards Earth.

Well, for the sake of the original argument, I think you're wrong here: It
wasn't about a speed *boost*, but just using the black hole to "swing around"
and not lose any of the momentum that got us there in the first place.

Though you may be right that for the sake of this maneuver, *any* black hole not
sufficiently "static" with respect to us would be a bad choice. I didn't check
the math.

Then again, I think yours is wrong as well: With that black hole being
sufficiently heavy and having a speed of V, if we head there with a speed v, we
should be bouncing back at a speed of (roughly) v' = V-v (with no significant
influence of the hole's mass remaining), as long as neither of us is going
relativistic.

So it should suffice to find a black hole significantly slower than our
spacecraft.


>   Remember: When the Shoemaker-Levy was on collision course against Jupiter,
> tidal forces broke it in 9 parts well before it reached the surface. And
> Jupiter is a lot less massive than the Sun.

I'd expect it to depend a good deal on (a) how elastic the thing is, and (b) how
fast the thing is rotating around itself: When rotating fast, the tidal forces
not only tear at the electromagnitic "links" between the molecules and atomic
particles, but keep distorting the shape of the object, and I guess an overdose
of squishing and squashing kills an object a lot faster than the tidal forces
themselves.

It's similar to a tyre with not enough air pressure: As long as you don't move
your car, nothing bad will happen to it. But if you drive around with it too
fast, the squishing and squashing will heat it up, so it may ultimately break
up like that comet...

So, in this sense, the Shoemaker-Levy comet wasn't torn apart by tidal forces,
but was killed by RSI :)


>   They don't emit anything, but by their nature as being really massive
> objects they surely tend to aggregate lots of nasty stuff orbiting around
> them, and this stuff often emits large amounts of radiation by several
> means.

Well, would they aggregate more stuff than a massive star? (Assuming we're
talking about "star-sized" holes here)


>   For example one concern about sending probes to orbit Jupiter is the
> large amount of radiation there (which could break electronics if not
> shielded properly). Jupiter, as a very massive object, gathers tons of it.
> And Jupiter is a lot less massive than a normal black hole.

Maybe that's due to a magnetic field of Jupiter? Sort of a "Van Allen Belt,
XXL-size"?

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