On Fri, 09 Sep 2005 18:14:54 -0400, Yousuf Khan
wrote:
Hawking radiation would take effect even on the most massive BH's
hundreds of trillions of years from now, when the matter in the galaxies
has run out and there's nothing left to still fall into a BH.

That's assuming you believe in the cold, dark forever expanding universe
theories.

I seem to recall reading somewhere (the standard ever-helpful
reference on Usenet that there's a lower limit to the cosmic
background radiation's temperature due to some quantum-mechanical
effect, no matter how much the universe expands. If that's the case
then it might be possible in some of those ever-expanding universe
theories for black holes to continue growing forever too. However,
this is a volatile field right now so I've no idea whether the idea
still has currency.

On Fri, 09 Sep 2005 18:11:32 -0400, Yousuf Khan
wrote:

AA Institute wrote:
The stellar BHs come about from the destruction of stars, but I wonder
what the theories are about the origins of supermassive (galactic core)
BHs?

They were likely already born big when the first galaxies emerged from
the Big Bang. But they also likely merge from smaller BH's and neutron
stars.

http://en.wikipedia.org/wiki/Interme...ass_black_hole has some
information about this kind of thing. It makes sense that such
beasties would exist, but apparently the jury is still out on whether
evidence for any has been found yet.

Bryan Derksen wrote:

I seem to recall reading somewhere (the standard ever-helpful
reference on Usenet that there's a lower limit to the cosmic
background radiation's temperature due to some quantum-mechanical
effect, no matter how much the universe expands. If that's the case
then it might be possible in some of those ever-expanding universe
theories for black holes to continue growing forever too. However,
this is a volatile field right now so I've no idea whether the idea
still has currency.

Hawking-Unruh radiation, which occurs whenever there is an event
horizon. If the cosmological constant is nonzero, objects that
are sufficiently far away from an observer become unreachable,
so each observer is surrounded (at sufficient distance) by
an event horizon.

However, as I understand it, any black hole that would fit
in this universe would have a temperature greater than the
temperature of this universal event horizon, so it could
not grow by absorbing this radiation.

Paul

"Bryan Derksen" wrote in message
...
| On Fri, 09 Sep 2005 13:33:04 GMT, "Androcles" Androcles@ MyPlace.org
| wrote:
| | You can see planets in other galaxies?
| |
| | You were talking about stars colliding.
|
| Yes indeed I was. I was also talking about a comet, Shoemaker-Levy,
| colliding with Jupiter in 1994, and I just can't help noticing
craters
| on the moon.
|
| You're jumping around rather a lot here.

I'm taking about collisions. Meteor showers to supernovae, all emit
light.
The word nova means 'new', originally used as 'new star'.

|The initial subject of
| discussion was your proposal that at least some supernovae are caused
| by stars colliding, and 1987A was a supernova, so that would have been
| a matter of stars colliding rather than anything to do with planets.

I don't know that, I'm considering it is a possibility. It may have been
a planet that collided with a star. I'm not stuck in the groove that
supernovae are spontaneous single body events.

| The craters on Earth erode, of course, but Google
| Earth will show the remnants. Then there's Mercury, another
| cratered world.
| It seems collisions are more common that you are capable
| of imagining but are very good at making wild guesses about
| there frequency.
|
| Collisions between planets and asteroids are common, for very
| well-understood and explainable reasons - they're all packed in quite
| close together.
|
| Stars, on the other hand, collide very rarely indeed for equally
| well-understood and explainable reasons - they're extremely _loosely_
| packed, and most don't move all that fast relative to the distances
| between them, Globular clusters are one place where this is an
| exception, there are stars in them that astronomers currently believe
| are the result of two other stars colliding and merging together. Look
| up the term "Blue straggler" for more information.
|
| | I'm not going to be responding any further to this though. I'm
offline
| | for a bit.
|
| Run away then.
|
| Do try to be civil. People have been trying to help you here.

I don't need their help. I'm trying to help them.
I certainly don't need help from the likes of Tim Auton,
"Collisions occurring does not make collisions the cause of supernovae."
What does the fool think he'd see? A firecracker?
Nor do I need it from who it would appear
used a time machine to travel to 1054 and knows that "The Crab Pulsar
is the remnant of a pretty standard Type II Supernova."
Why should I suffer fools gladly?

Your very loosely worded "explanation" only explains the way you think,
it doesn't explain supernovae. If two stars were to collide, the result
would be a supernova. All it takes is for one to drift close to another,
slingshot away from each other and one of them head straight toward
another star. The possibility of collision is then greatly enhanced,
trajectory rules the event.
The "blue straggler" concept is a good one, and the Crab pulsar is a
fine
example of underestimation of what a collision would produce.
Ever played pool or billiards? Those that do know instinctively what
putting "side" ("english" if you are American) will do to the angular
momentum of the cue ball.

Androcles.

wrote:
Hi Al,

Interesting thoughts there about what is possible to happen in the
immensities of the far future...

So if supermassive black holes at the centers of galaxies continue to
grow and expand as they feed on more of their surrounding stellar
material... would it not seem feasible to think that the universe will
eventually be left with no bright stars or galaxies at all, but just an
endless expanse of emptiness with just the odd giant black hole (that
was once the core of a galaxy), drifting in the dark... ?

Bleak.... bleak... outlook

If the expansion of the universe is accelerating, and it continues to do
so, then everything will eventually get ripped apart, atoms, everything!
Yes, bleak, but so far off in the "way beyond" that, well, it is not all
that bleak after all. We'll have billions and billions of years to enjoy
the Galaxy (that is if we don't self distruct first!! --- that is the
real problem --- right up close to our nose at this time). I keep hoping
that at least some humans will be able to leave Earth before it is too
late :-) At least some members of humanity will survive :-) ... I know,
I'm being a little dramatic here :-) Go NASA, ESA, ?! You're our only
hope! :-)

The binding energy of matter (gravitational force of the galaxy, stars,
planets, the electrical forces, the strong forces holding atoms
together, all that stuff) will prevent the big rip being a factor until
far far off into the future ...


OT: What is the current best-fit theory about how things are likely to
end. Is it still the so-called 'Steady-state' theory I wonder...

The steady state theory (there are still some fans of this hanging out
at UCSD :-), the Burbidge's, I like them, I hope they are still alive, I
don't know) has become OBE (overtaken by events) by the "big bang"
theory ...




AA
------------------------------****---------------------------*-*--------

http://www.publishedauthors.net/aa_spaceagent/
"The ultimate dream adventure awaiting humanity..."
------------------------------****---------------------------*-*--------

In
sci.astro.seti,sci.astro,sci.physics.relativity,re c.arts.sf.science,
On Fri, 09 Sep 2005 17:34:24 -0700, Erik Max Francis
wrote:

Rob Dekker wrote:

{ snip calculations }

So we should be (by definition) in a black hole...

Except we're not, because the Universe is expanding. The Universe
appears open, and furthermore the expansion appears to be accelerating.
Saying that "by definition" we're in a black hole only makes sense if
you're making some useless semantic distinction, rather than talking
about the actual physical properties of a black hole.

Presuming for a moment that we ARE in a big black hole, why are we
not compressed into an infinitesimal point at its center?

: Ben Bradley
: Presuming for a moment that we ARE in a big black hole, why are we
: not compressed into an infinitesimal point at its center?

Because it takes a finite amount of time to fall that far.


Wayne Throop http://sheol.org/throopw

Gravity is not attraction between masses. Black holes, if they existed,
curve space where objects move along geodesic paths. Black holes don't eat
stars. That kind of happening would as exceptional than the Sun eating
planets in our solar system.

Henry Haapalainen


"Alfred A. Aburto Jr." kirjoitti viestissä
...
wrote:
Hi Al,

Interesting thoughts there about what is possible to happen in the
immensities of the far future...

So if supermassive black holes at the centers of galaxies continue to
grow and expand as they feed on more of their surrounding stellar
material... would it not seem feasible to think that the universe will
eventually be left with no bright stars or galaxies at all, but just an
endless expanse of emptiness with just the odd giant black hole (that
was once the core of a galaxy), drifting in the dark... ?

Bleak.... bleak... outlook

If the expansion of the universe is accelerating, and it continues to do
so, then everything will eventually get ripped apart, atoms, everything!
Yes, bleak, but so far off in the "way beyond" that, well, it is not all
that bleak after all. We'll have billions and billions of years to enjoy
the Galaxy (that is if we don't self distruct first!! --- that is the
real problem --- right up close to our nose at this time). I keep hoping
that at least some humans will be able to leave Earth before it is too
late :-) At least some members of humanity will survive :-) ... I know,
I'm being a little dramatic here :-) Go NASA, ESA, ?! You're our only
hope! :-)

The binding energy of matter (gravitational force of the galaxy, stars,
planets, the electrical forces, the strong forces holding atoms
together, all that stuff) will prevent the big rip being a factor until
far far off into the future ...


OT: What is the current best-fit theory about how things are likely to
end. Is it still the so-called 'Steady-state' theory I wonder...

The steady state theory (there are still some fans of this hanging out
at UCSD :-), the Burbidge's, I like them, I hope they are still alive, I
don't know) has become OBE (overtaken by events) by the "big bang"
theory ...




AA
------------------------------****---------------------------*-*--------

http://www.publishedauthors.net/aa_spaceagent/
"The ultimate dream adventure awaiting humanity..."
------------------------------****---------------------------*-*--------

it's - its

AA, much of the material is shot /out/ of the galaxy.

Henry Haapalainen wrote:
Gravity is not attraction between masses. Black holes, if they existed,
curve space where objects move along geodesic paths. Black holes don't eat
stars. That kind of happening would as exceptional than the Sun eating
planets in our solar system.

Stop cascading! Gravity is. Two suns can.