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Q:
I read in a book that an average adult astronaut would die if
he/she was sucked into a black hole miles before the person was
even near the black hole. Is that because the amount of gravity
being sucked in by the black hole is crushing the person?
A:
The force of gravity on the side of the astronaut closest to the
black hole would be stronger than on the side farthest away, so
the astronaut would be stretched in the direction of the black
hole. Eventually this force would rotate an astronaut lengthwise
so that his/her head or feet would be lined up with the
direction to the black hole. By the time the astronaut was 3,000
miles or so away from a black hole containing ten times the mass
of the Sun, these forces would pull all the blood to the end
closest to the black hole, with fatal effects. As the astronaut
got closer, his/her body would be torn apart. So, the gravity in
the vicinity of the black hole would pull a person apart before
it crushed him/her.
The same effect causes the Earth to be pulled slightly out of
round by the Moon's gravity, and causes the ocean tides. For
this reason the forces are called gravitational tidal
forces.
Reference: Kip Thorne, Black Holes & Time Warps
(W.W.Norton, New York, 1994)
 For more information see our Field Guide section on Black
Holes.
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