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Fraser
2005-Apr-15, 06:19 PM
SUMMARY: Here's a relief. Instead of being painfully stretched (aka spaghettified) by the immense tidal forces around a black hole, you'd probably just be roasted by the intense heat. Professor Andrew Hamilton at the University of Colorado predicts that only the smallest black holes would actually stretch you out like this. All the larger, supermassive black holes are already choking on enough material, that their surrounding environment is a superhot plasma heated to millions of degrees and blasting out intense radiation.

View full article (http://www.universetoday.com/am/publish/roasted_black_hole.html)

What do you think about this story? Post your comments below.

GOURDHEAD
2005-Apr-15, 07:11 PM
Quoted from the article:

Most people have heard of the event horizon of a black hole, as the point of no return. But astronomically realistic black holes are more complex and should have two horizons, an outer and an inner. In the bizarre physics of black holes, time and space are exchanged when you cross an event horizon, but at a second horizon they would switch back again.

Traveling into a black hole, you would therefore pass through a strange region where space is falling inward faster than light, before finally entering a zone of normal space at the core. It's this core of normal space which Professor Hamilton has been working on.

A so-called singularity sits at the centre of the core, swallowing up matter. But according to Professor Hamilton, the strange laws of general relativity temper its appetite. If the singularity ate too quickly, it would become gravitationally repulsive, so instead, matter piles up in a hot, dense plasma filling the core of the black hole and siphoning gradually into the singularity. However did he come to such a conclusion?

When time and space are exchanged, do we expect 3 dimensions of time and one of space?

Clong
2005-Apr-15, 07:43 PM
I agree with Gourdhead. Professor Hamilton needs to re-think his hypothisis, and explain it further. I agree that you probably would burn up, but it would be way before you even reached the event horizon (unless you were sheilded by some miracle, yet to be discovered). But I don't agree with his hypothosis about the gravitational pull being less on a massive blackhole over a smaller one, or that it would eventually repel. I see no evidence of this ever being the case.

I also see no evidence of normal (or near normal) space time being somehow restored near the singularity. I would love to see his rationalization of this.

Greg
2005-Apr-15, 08:56 PM
How comforting to be only roasted into plasma rather than stretched into spaghetti hundreds of light years long. I do have reservations about some of this author's conclusions. I would love to hear Stephen Hawking rebuke this one. I never plan to be anywhere near a black hole, given it were even possible for me to travel to one in my lifetime.

Guest
2005-Apr-15, 09:58 PM
Then your ashes are spagettified...

ravik521
2005-Apr-16, 02:43 AM
Duh people. Black holes are like the recycling bin on your computer. It sucks in things and destroys them. All they do is create destruction. People lets hope planet earth doesn't get sucked in by one. If it does, god help us all. But if we were we would know about it. B)

Mr. Smartypants gamer guy
2005-Apr-16, 05:37 AM
if it is incinerated what hapens to the theory of the perfect liquid inside a blk hole? and why i mean most people make it seem as its just crushed to become super ultra tiny and stuff...

IAMU
2005-Apr-16, 07:02 AM
Blackholes I believe do not destroy or annilate but rather transforms... CHANGES matter. Why do we look at things that have and end... how long is a piece of string.
Lets also look at the beginning... it has many possibilies...CREATION for example. Change and Creation are part of all things...nothing could exist otherwise. We have been through 2000 years of Change...DEATH...are we truly living ?. Now we are beginning to learn about Creation... BIRTH... Oh' my God, there is life after death.
We Truly need to understand both sides of the story to make all things whole....so lets not only look at blackholes as the END... but also a BEGINNING. With this in mind we align both hemispheres and see totality in all things... to become Masters of our own Universe. There is no need to be afraid of this ! :rolleyes:

Guest_Parvenu
2005-Apr-16, 09:57 PM
I think that we have a lot of work ahead to convince the Trekies that Black Holes are NOT "Worm Holes" which one uses as a handy tunnel to travel to some conjoining universe! I think that public statements that extreme matter to energy transformations (without a "matter transponder" to reassemble us from energy) are permanent and mean the end to life as we are currently experiencing it are very beneficial. I am sure that the Trekies will thank us someday.

wstevenbrown
2005-Apr-16, 10:36 PM
But I don't agree with his hypothosis about the gravitational pull being less on a massive blackhole over a smaller one

This part is almost translatable. According to Hawking, an increase in mass by a BH results in a proportional increase in the area of the event horizon, not its volume. Therefore, a more massive BH has a gravity gradient that is less steep (the rate of change is slower) than that near a lower-mass BH. The field of the more massive one, however, stays strong longer (to a greater distance).

Here's the counterintuitive part: It is also true that a more massive BH is less dense than a less-massive one = less mass per unit volume. This argument can be continued for BH's of indefinitely large mass...

Check my facts-- I'm away from my library, and may have misremembered. All that stuff in the interior, tho, would probably raise good rose bushes.

Best regards-- Steve

dave_f
2005-Apr-17, 06:11 AM
Originally posted by Mr. Smartypants gamer guy@Apr 16 2005, 12:37 AM
if it is incinerated what hapens to the theory of the perfect liquid inside a blk hole? and why i mean most people make it seem as its just crushed to become super ultra tiny and stuff...
Either you are fried or are streched into spaghetti. Either way, you are mince meat.

The important factor in all of this is the question "Will I make it near anywhere near a black hole?" The answer to that question is "NO".

Emily
2005-Apr-17, 09:54 AM
well thats good to know when I'm in a black hole! hehehehe! Very interesting. How was this discovered? :huh:

Planetwatcher
2005-Apr-17, 10:35 PM
Instead of being painfully stretched (aka spaghettified) by the immense tidal forces around a black hole, you'd probably just be roasted by the intense heat.I'd have to tell the Professer, "I don't think so." Let reason rule for just a minute.

If the event horizon is the point where not even light can escape from the black hole, and light travels faster then heat, then it stands to reason there is a point approaching the black hole where heat can no longer escape either, and it would be well before you reach the event horizon.
Therefore, by the time you reach the event horizon, there will be no heat, because it will have joined with the singularity in the center. Even as you cross the event horizon and dimensions change places with time, there is still no heat for it has already joined the singularity.

The effect of being stretched into spaghetti should actually be stronger in a larger black hole, because the object which became the black hole would had to have been larger with more mass, meaning more gravity, and a larger vaccum to fill.

qraal
2005-Apr-18, 10:57 PM
Guys you're all misunderstanding the news bite. What Hamilton is describing is on the other side of the Event Horizon as you're falling into the singularity - but the singularity of a real astrophysical black hole, not an idealisation. He's had to account for the matter that formed the singularity giving the hole a net charge and magnetic field. This creates a second inner event horizon. Between the inner and the outer horizons ONE space dimension has been swapped for time, the dimension pointing radially inwards to the singularity. But cross the inner horizon and it's regular space again, but the singularity - being an infinitesimal point - can't swallow mass too fast or else it ends up with a net negative mass that repels.

As for the strength of gravity - it's huge - but tidal forces go up with the inverse CUBE of the radius, while black hole radii go up with the mass linearly. Therefore at some mass the TIDAL forces are very low, even if the gravity is humungous too. To stand still just above the event horizon would require an immense counter-acceleration but in a free-fall trajectory only the tidal forces (the rate of change in gravity with distance) will be noticed.

Actually a black hole with the mass of the Local Group of Galaxies (~ 3 x 10^12 solar masses) would have a surface gravity of 1 gee, so surface gravity doesn't have to be ultra-huge either. How big would the hole be? One solar mass is a Schwarzchild radius of ~ 3 km, so the Super-Hole would be ~ 1.9 light-years across. Tidal forces need an even smaller radius - 1 gee tides need a hole of just 32,426 solar masses, some 191,500 km across. The Milky Way's 3 million Solar mass BH at the Core would be ~ 18 million km across and have 1/1,000,000th gee tides.

Unexpected hey? But Black Holes are like that, very counter-intuitive. Hamilton's theory is based on general relativity, but it may not be correct. There's a major problem caused by black hole entropy which is unanswered by general relativity, but might have a quantum solution. A new theory has been developed that describes the insides of the Black Hole as an Bose-Einstein Condensate, which causes anything impacting to be reduced to energy.

Thus you're toast before you even get past the Event Horizon.

qraal

Guest
2005-Apr-19, 09:56 PM
The solutions in which black holes are assumed to be empty except
at the singularity (i.e. in which the only contribution to the energy-momentum
tensor is from an electric field sourced by charge concentrated at
the singularity) are the well-known Reissner-Nordström and Kerr-Newman
solutions. These solutions are gravitationally repulsive in their
cores. For a rotating black hole, the repulsion is from the centrifugal
force. For a charged black hole, the repulsion is from the negative
radial pressure of the electric field.

The only kind of black hole that is attractive all the way to the
singularity is a BH with no charge and no rotation -- the Schwarzschild
solution.

It follows that empty rotating or charged black holes are not consistent
end-points of gravitational collapse -- how could charge and matter end up
entirely in the singularity if the core of the BH is repulsive?

This much is well-known to general relativists.

The question then is, what actually happens, if an empty black hole
cannot happen? This was the question addressed in 2 papers which
have now been accepted for publication in Physical Review D:
http://arxiv.org/abs/gr-qc/0411061
http://arxiv.org/abs/gr-qc/0411062
Warning: these papers are quite technical and full of equations.

Part of the solution to the problem is that there is a well-known
instability that occurs close to the inner horizon of a charged
or rotating black hole. This instability, first pointed out by
Poisson and Israel (1990), leads to a phenomenon they called
"mass inflation". Our paper
http://arxiv.org/abs/gr-qc/0411062
contains a physical explanation of what mass inflation is and
what causes it.

One of the features of the mass inflation instability is its violence.
Usually when one perturns a solution (such as the Kerr-Newman solution)
by a tiny amount, then the solution changes only a little bit.
In contrast, the mass inflation instability has the property that
the smaller the initial perturbation, the more rapidly the perturbation
grows. A tiny tiny perturbation produces rampant mass inflation.

The other part of the solution is, what happens as a consequence
of the mass inflation instability? In our model, we found that the energy
generated during mass inflation is converted to a hot, dense plasma
which fills the core of the BH up to its inner horizon.

We do not have a general proof that a hot dense plasma is the
necessary consequence of the instability in all cases, but it is
does seem a natural outcome, and I am inclined to suspect that
a hot dense plasma at the core of a BH is generic. Whatever the
case, we know that the BH cannot be empty.

I agree that it is disappointing that the wormhole solutions
which connect the insides of empty black holes to new Universes
(or to other places in our Universe) are unstable, and I would hate
to assert that people in the future will not be able to craft
wormholes for travel in spacetime. However, if one considers
astronomically "realistic" black holes (which is what our papers
attempted to model), then wormholes seem quite unlikely.

> and when time and space
> exchange do we expect to have 3 time dimensions and 1 of space?

No. Only the radial direction becomes timelike. The horizontal
directions remain spacelike. So still 3 space + 1 time dimension.

> What do you mean by inner horizon?

The inner horizon is a 2nd horizon that occurs in charged or rotating
black holes inside the event horizon.

It is legitimate to imagine space as falling into a black hole
(in the Schwarzschild solution, at the Newtonian escape velocity).
Outside the (outer, event) horizon, space falls at less than the speed
of light. At the horizon, space reaches the speed of light,
and inside the horizon, space falls faster than light.

In charged or rotating BHs, the core of the BH is repulsive,
so the inflow of space slows back down. The place where it
slows back down to the speed of light marks in the inner horizon.
It is at this point that there is the violent mass inflation instability.
If it were not for the instability, the inner horizon would mark
the gateway to a wormhole: the flow of space turns around, and then
accelerates back out through a white hole to a new Universe.

> I thought nothing can move faster than light?

Nothing can move *through* space faster than light. But in general
relativity, space itself can effectively move faster than light.
In a black hole, space inside the outer horizon falls faster than
light, which is why light cannot escape: the light is dragged
inward by the flow of space, even if the light is pointed outwards.

> I agree that you probably would burn up, but it would be way before you even reached the event horizon

Observed black holes are typically surrounded by a hot accretion disk.
But this is not a mathematical requirement. In principle a person
could fall into a BH without being burnt up first.

> But I don't agree with his hypothosis about the gravitational pull being less on a massive blackhole over a smaller one

A black hole which is more massive is also larger in radius,
with radius proportional to mass. The tidal force goes as
mass/radius^3, and is therefore weaker at the event horizon of a
more massive black hole.

In supermassive BHs such as the one at the center of our Milky Way galaxy
(mass = 4 million suns), the tidal forces are weak enough that you
would likely survive down to inner horizon, where you would encounter
the mass inflation instability and be incinerated.

> A new theory has been developed that describes the insides of the Black Hole as an Bose-Einstein Condensate, which causes anything impacting to be reduced to energy.

Classically, nothing strange happens at the outer horizon. The recent
claims are that somehow quantum mechanics causes divergences near the
horizon. I do not see how that can happen, and would welcome a clear
explanation.

By contrast, there is a very real instability at the inner horizon.

Andrew Hamilton
University of Colorado

qraal
2005-Apr-20, 01:00 AM
Hi Andrew

Thanks for the clarifications. Glad I didn't get your theory entirely wrong - I really don't understand the mass inflation thing at all, but I'll try and read that paper again.

Is the Reissner-Nordstrom metric astrophysically realistic? Wouldn't charges tend to be cancelled? I guess charge separation by weird MHD in the accretion disk might work. When I first skimmed your paper I thought it was for just RN metric not the Kerr-Newmann.

qraal

Mr. Smartypants gamer guy
2005-Jun-03, 11:24 PM
tsk tsk tsk, you all should know by now that black wholes are all part of energy and if you look at the string theory - its realy cool! - that gravaty is a particle and since a black hole is the ultimatum particle then a black hole is the ultimatum object, untill we find somthing stronger than a black hole then well the universe goes to the black holes. you know ther is this one episode of the simpsons where homer finds this odd dimention and acidentily breaks it. it kinda turns into a blk hole and the universe is gone after all this hapens. note this could hapen to us unless we find out how to reverse it. pluss with my infinte expanding brain, not unlike the univerese, which i can grasp how big it is oddly enough... we need to know why it was made how it was chosen (the design for it) and exactly what single pice of info in all this determins what goes what why somthins is what it is and most imporantly the start button who pussed it things just dont start on tehre own! somthing somehow pushed it and we are here now.... so blk holes... good? bad? nutral? nope just eating away and consuming and growing they are the stop buttons kinda... they have to stop what somthing (whatever it was) started...? :ph34r:

Mr. Smartypants gamer guy
2005-Jun-16, 05:23 PM
DONT U GUYS EVER TALK TO ME!

qraal
2005-Jun-19, 02:39 AM
Gamer_Guy

We'd be happy to talk but the spelling mistakes are kind of distracting. So what do you want to talk about Black Holes?

qraal