The Doctor wrote:

David Bromage wrote in
:


Martin Dunne wrote:

It's certainly very unusual, but I like the reasoning! The problem
isn't just one of origin, although that makes it really unlikely.
It's tidal force, bit of a misnomer as there's no such force, just
the observation off the back of this planet's oceans that gravity
pulls slightly more on the forward side of a facing object. When
dealing with gravity of this order this translates into a lot of
disproportionate pull.

And not on the ocean (there wasn't any) but on the rock, such that the
planet would be distorted to the extent that a Mt Everest could be
pulled up on the side closest to the black hole every rotation. The
friction alone would guarantee that there would be little if any solid
crust and the surface of the planet would be akin to our mantle.

Also the orbital period of a planet that close would be measured in
hours rather than days, weeks or months.



Doesn't Jupiter's moon Io has active volcanoes because of tidal forces
from Jupiter's gravity? If that's case, how would a planet around a
black hole survive for long? Or at least, it may be able to have a solid
surface.

It's all a question of distance. If the planet is suitably far from the
black hole, then it will not suffer such disruptive tidal effects.

People often seem under the impression that a black hole has a specially
high gravitational field. It doesn't. It has exactly the same
gravitational field as any other object of the same mass. The mass of
the black hole does not have to be particularly high by stellar standards.

It's a bad idea to get close to a black hole, but then it's a bad idea
to get close to any massive object.

Sylvia.