Re: That Black-Hole Space-time curvature thing

Anders Sandberg (
14 Sep 1997 19:51:16 +0200

Keith <> writes:

> I wonder how, if at all, this result varies depending on the mass
> of the black hole and its movement relative to the observer.

Heavier black holes have gentler tidal effects, so you will
survive a bit longer. As for the relative motion, I don't
think it will change much unless you or the hole are strongly
relativistic. Oh, yes, to bring up a current thread on, if you fall towards the hole along
a non-radial orbit you will likely experience strong torques
too, so if you miss the hole the resulting spin might kill you.

Kids, remember that playing near black holes can be dangerous!
Always ask you parents for permission first.

> What if a particle, say a neutron, that was moving very fast -so
> close to the speed of light that it's mass was equal to the
> earth's mass -were to hit the earth dead center? Would the
> particle just pass on through? Or would it hit other particles,
> which in turn would hit more (other) particles, to such an extent
> that the earth would be destroyed? Would there be an "entry
> wound" and an "exit wound?"

I think it would depend a lot on the particle, some particles
interact weakly with matter (like neutrinos) while others
interact strongly (like alpha particles). A neutrino would
likely just sweep through with no effects, while the alpha
particle would likely crash. In the crash some of its
kinetic energy will be transferred to other particles, creating
a cascade. If its relativistic mass was equal to the mass
of the earth, then I think it is quite safe to assume that
there will be no exit wound - there will be no planet,
and likely no moon, left...

> What if the particle were moving so
> fast that its mass were 1 solar mass? 5 solar masses?

We are getting up in the gammar-ray burster class here. The sun converts
around one ton of mass into energy every second (I think, can somebody
corraborate this?); converting one earth mass into energy would likely
be in the supernova range. Converting stellar masses into energy would
be visible across the universe, and really mess up things nearby.

Just to get an impression of the power we are talking about, take
a look at, which shows
some of the local interstellar medium. Those 100-lightyear bubbles
are likely due to ordinary supernovas...

Anders Sandberg                                      Towards Ascension!                  
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y