How come black holes are so massive?

[Gawdzilla Sama]

Something to do with the fact that information can't be destroyed?

Ha! I wrote down my password yesterday and it's nowhere to be found.

It's pa$$word - same as you always use. And don't ask me to remind you again!

About what?

Just take some more of your pills...

Which?

[Xamonas Chegwé]

Just take some more of your pills...

Which?

The really strong placebos.

[Gawdzilla Sama]

Just take some more of your pills...

Which?

The really strong placebos.

I got some that can curl 250 kg.

[JimC]

Something to do with the fact that information can't be destroyed?

Ha! I wrote down my password yesterday and it's nowhere to be found.

It's pa$$word - same as you always use. And don't ask me to remind you again!

About what?

Just take some more of your pills...

Dried frog pills are always good...

[mistermack]

Isn't the question the wrong way round? Anything so massive, can't be anything else BUT a black hole. Once fusion dies down.

The real question is, why do things get so massive? My limited astrophysics seems to remember that the moon is moving away from the Earth, because of tidal friction. So why doesn't that happen to stars, orbiting black holes? Why don't all large bodies move apart in the same way? Maybe they get upset, when a third massive body drifts near, and upsets the apple cart.

[Calilasseia]

Isn't the question the wrong way round? Anything so massive, can't be anything else BUT a black hole. Once fusion dies down.

Actually, there are plenty of massive objects that ]i]aren't[/i] black holes. Neutron stars are an example thereof. Which are prevented from collapsing into black holes because nuclear degeneracy pressure is sufficient to resist gravity. They don't have quite enough mass to collapse all the way into black holes.

The real question is, why do things get so massive?

Gravity acting upon sufficient material present to allow a large-mass star to coalesce.

My limited astrophysics seems to remember that the moon is moving away from the Earth, because of tidal friction. So why doesn't that happen to stars, orbiting black holes?

If they're orbiting at a sufficiently safe distance, it does. This stops being an issue if the star is orbiting sufficiently close to a black hole.

Why don't all large bodies move apart in the same way? Maybe they get upset, when a third massive body drifts near, and upsets the apple cart.

See above.

[Horwood Beer-Master]

Surely in theory a black hole needn't be relatively massive, as long as it has some mass; all that's important is the density.

Of course any black hole that's really low-mass would evaporate nearly instantly (unless Hawking turns out to be wrong - then it wouldn't), and below a certain mass some atypical explanation is required for how it formed in the first place. But that aside, there's nothing to prevent a black hole having a mass equivalent to that of the Sun, or the Earth, or even a pint of beer. It would still be a black hole, if a somewhat hard to explain one.

I would however be pissed-off if the pint I was about to drink collapsed to form black hole. Also shit-scared, but mainly pissed-off.

[Clinton Huxley]

It was hell in the Black Hole Of Calcutta.

[JacksSmirkingRevenge]

Caught by the Nawab, eh..? Nasty.

[Gawdzilla Sama]

Caught by the Nawab, eh..? Nasty.

Better than getting caught by the Na'vi.

[mistermack]

My limited astrophysics seems to remember that the moon is moving away from the Earth, because of tidal friction. So why doesn't that happen to stars, orbiting black holes?

If they're orbiting at a sufficiently safe distance, it does. This stops being an issue if the star is orbiting sufficiently close to a black hole.

The question was why?

[Gawdzilla Sama]

My limited astrophysics seems to remember that the moon is moving away from the Earth, because of tidal friction. So why doesn't that happen to stars, orbiting black holes?

If they're orbiting at a sufficiently safe distance, it does. This stops being an issue if the star is orbiting sufficiently close to a black hole.

The question was why?

Because the gravity isn't strong enough to keep them. Same as the Earth's gravity won't keep the Moon.

[mistermack]

My limited astrophysics seems to remember that the moon is moving away from the Earth, because of tidal friction. So why doesn't that happen to stars, orbiting black holes?

If they're orbiting at a sufficiently safe distance, it does. This stops being an issue if the star is orbiting sufficiently close to a black hole.

The question was why?

Because the gravity isn't strong enough to keep them. Same as the Earth's gravity won't keep the Moon.

No, the Moon is moving out, because the tides are reduciing the kinetic energy of the system.

All systems have tides, even solid rock squeezes and pulls into slightly different shape, as it orbits.
So how come orbiting bodies don't ALL move apart?

[Gawdzilla Sama]

"Orbital Mechanics", it's a college level course.