Warp <war### [at] tagpovrayorg> wrote:
>   With this taken into account, can you just go from Earth to the nearest
> black hole, get an enormous speedup and come back at 100x the speed and
> slam onto Earth at that speed? From a gravity assist only, I don't think so.
> I think it would be against conservation of energy. If you were travelling
> from Earth to another star system, then maybe, but I don't think it works
> in the closed case.

It does.

The trick is that the slingshot affects both bodies: That Huge Planet Over There
and yout Teeny Weeny Space Machiney.

Guess which one *seems* to be affected most...


So if you use a black hole to slingshot you around back home, at the same time
you sort of slingshot the black hole around your spacecraft into the opposite
direction... it's just that the black hole won't bother *much*, being the fat
lazy sucker it is.

> - If you go so close to a black hole that it will give you a stronger
> slingshot effect than a regular star would, the tidal forces would
> probably rip you apart. Not very practical.

Nah, I don't think so. Would tidal forces rip you apart at the surface of the
sun? I doubt. At half the star's radius you already get 4 times the
gravitational pull, but only about 2 times the tidal forces (gravity being
proportional to the inverse radius' square, so its gradient being only linearly
proportional to the inverse radius, if I get the math right).


> - Black holes usually have an accretion disc around them, usually much
> larger than the size of a normal star of the same mass. The accretion
> disc could slow you down or be dangerous.

Only if they are supermassive (those you'd expect to find at galaxy centers) or
happen to have a companion star.


> - The humongous amounts of radiation around a black hole would probably
> be enough to fry you to ashes in a fraction of a second, no matter what
> kind of shielding you use, especially if you go so close that you would
> get a larger speed boost than from a regular star.

Again, only if there's an accretion disk. Remember: Black holes don't emit
anything - only their surroundings may ;)


However, maybe you also want to check the magnetic field of the black hole - I'm
not sure about the orders of magnitude, but I wouldn't want all my electrons go
spinning off to the left while the protons go off to the right - not to speak
of the resulting synchroton radiation ;)

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