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Black Holes
maryalien
post Dec 7 2005, 04:04 PM
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any one wanna talk black holes. i'm not a professional or anything. i vaguely remember hearing s. hawkin revising his opinion on it saying it wasnt a "worm hole" anymore and that it just destroys all matter and worth nothing else.

i only make my observations, childlike actually, to that of what happens on earth, and why shouldnt it happen in the rest of the universe. why should anything here (goverening law of physics, etc.) be different anywhere else?

just like a tornado, or water running down a drain (or that infamous lake that was drained by accident by some guys drilling and all the water drained into the salt mine, i cant remember the name now but a 6 inch hole sucked in a tanker), why wouldnt a black hole be that "event" that punched a hole into another "dimension/galaxy whatever" with less pressure.

and maybe all that "dark matter" is the "reminant" of what comes out of a black hole.

i dont know, just talking. my head is always "out there, out of earth..."

maryalien
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mike
post Dec 7 2005, 06:05 PM
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Actually I think Hawking recently said that some information does remain intact in a black hole.

Personally though I'm not sure how anyone can really say what happens in a black hole, having never gone into one or even being especially close to one, so far as we can tell..
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Jeff7
post Dec 7 2005, 07:19 PM
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...which is why his field is theoretical physics.smile.gif
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dvandorn
post Dec 7 2005, 08:20 PM
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First, though it's likely redundant for most of the people here, let's talk some basics about black holes.

Black holes are all about the relationship between mass, energy and gravity. Gravity is a function of mass -- the more mass you have, the greater gravitational influence it has on surrounding masses.

Gravity even affects photons and other energy "particles." A black hole comes into being when a body has so much mass that any particle of mass or energy that approaches it would have to accelerate faster than the speed of light in order to escape it.

That would be relatively easy to understand, if it weren't for the predicted effects of special relativity. Einstein's classic E=MC^2 equation states the relationship between mass and energy -- that a given amount of energy (E) is equal to the square of a given amount of mass (M) traveling at the speed of light ©. That's been taken to mean, rather simplistically, that mass cannot be accelerated all the way to the speed of light, and if it were, it would transform entirely into energy.

More importantly, special relativity also states that the passage of time is relative to how fast you are traveling compared to another point in space. The faster you go, relative to a given point in space, the slower time passes for you -- again, relative to that other given point in space.

When any mass passes the point near a black hole where it would have to accelerate to lightspeed or beyond in order to escape, the black hole's gravity would theoretically accelerate any such mass beyond the speed of light. But since that's both impossible *and* the required effect of such strong gravity, what happens beyond that point is called a singularity -- it's a region of space where physics cannot describe or predict conditions. That line itself, beyond which no mass can escape, is called the event horizon -- since no information, not even photons, can come out from within that boundary and tell us anything about any events happening within.

As a mass approaches the event horizon and is suddenly accelerated to just short of lightspeed, the passage of time for that mass would slow to a near-stop. For us, observing from outside, time would pass normally and we would see time pass normally for the accelerated mass as it comes close to being swallowed -- but once again, if the matter is accelerated to or beyond lightspeed, then time passage for it ought to stop entirely, and our physics can't describe what happens to mass that's frozen in time (at least, relative to the outside universe). So, once again, we have a singularity -- we just cannot describe what happens to the mass, how it might behave, or anything.

For a long time, it was thought that black holes sucked everything in, and nothing, not even the smallest amount of information about the black hole within or the mass falling onto it, would be able to escape. But we've found out that there are basically two kinds of information that *can* escape from a back hole: whether or not it's rotating, and whether or not it's electrically charged (and what the charge is).

You can tell if a black hole is rotating because its gravity field rotates with it, and the gravity field is the only really major thing that extends beyond the event horizon. You can observe this gravity field by looking at the effect it has on objects near the black hole. A spinning gravitational field accelerates mass both towards the black hole and along the rotation vector, so you can see and measure the rate of spin. (Again, an interesting thing, since we're observing a time-passage-dependent effect, rotation, outside of a system within which Einsteinian physics states that the passage of time should have stopped.)

Charge is also detectable based on how masses behave near a black hole. I'm not as knowledgable as to how we can determine the charge, but I know it can be done.

Spinning black holes also radiate mass and energy -- well, the disk around them does, anyway. The spinning gravitational field smashes infalling matter and energy into an equatorial disk. As matter swirls down towards the black hole, some of it follows a trajectory that accelerates it away from the black hole. The way it works (I dont have the math to explain the effect, I've just seen the results), the mass sprayed away from the black hole is shot out in jets from the rotational poles. And so, a spinning black hole can have the appearance of a child's top -- a spinning, spiraling disk rotating around the vertical "stick" of polar jets. The black hole within, of course, is invisible.

There has got to be some way in which quantum physics and multi-dimensional physics will eventually be able to describe the conditions that exist within the event horizon of a black hole. But, as of right now, no theories exist that account for all the known facts -- or that answer most of the outstanding questions.

Oh, and one other thing -- black holes aren't forever. They lose mass very slowly over the course of time (something else that I don't have the math to explain properly), and after many billions of years, they can simply evaporate. However, the theories as to what happens when a black hole falls back below the mass required to maintain the singularity are pretty raw right now. It's possible that massive amounts of energy are released, but it's also possible that the singularity doesn't collapse immediately at the point where the mass falls below that critical level.

I'm sure there are others out there who can fill in anything I've missed, and correct me if I've made any faux pas, here... but I think that's a pretty good starting point for any discussion.

-the other Doug


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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maryalien
post Dec 8 2005, 12:43 AM
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i got the feeling i was out of my league when i replied the first time, but your all so damned interesting, i love this stuff. really.

and i didnt know black holes diminish over time. i read an article saying that they vacillate, periods of "feeding" and dormancy. but naturally it must have its own life cycle, just like everything else and the universe...

thank you obe one
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Guest_Richard Trigaux_*
post Dec 8 2005, 08:21 AM
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QUOTE (maryalien @ Dec 8 2005, 12:43 AM)
i got the feeling i was out of my league when i replied the first time, but your all so damned interesting, i love this stuff.  really.

and i didnt know black holes diminish over time.  i read an article saying that they vacillate, periods of "feeding" and dormancy.  but naturally it must have its own life cycle, just like everything else and the universe...

thank you obe one
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maryalien,

I think you are in the right place here, if you are interested by astronomy stuff. We are most of us professionnal scientists or "enlightened amateurs", so what we often speak of things other people cannot simply understand. Dvandorn was kind enough to explain you some basics, I think it is great.

Black holes do not go through periods of activity and dormancy, but, in the center of a galaxy, the activity of the galaxy sends matter at times to the black hole, and at other times it does not. So the black hole is "active" or not, depending on the feeding it receives. But basically it is still here, increasing at each feeding period and never decreasing.

Oh, some scientists postulated they decrease, but it is at a scale of time billins and billions times the age of the universe. So practically in astrophysics we consider they do not decrease.

An interesting fact is that the smaller a black hole is, the faster it decreases, with more and more energetic radiations. So than when a small black hole ends its life, it produces more and more energy, light, X ray, gamma rays, ending in something very much like a nuclear explosion (although no waste remain).
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maryalien
post Dec 8 2005, 11:49 AM
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thank you for your explanations and time. i hope from time to time no one will mind if i can ask a question or two.

mar
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dvandorn
post Dec 8 2005, 01:52 PM
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Mind? Of course not! That's what we do here.

By the way, I did a bit of research and got an explanation for the evaporation of black holes. It seems that there is a phenomenon known to exist in the cosmos called "vacuum fluctuations." Basically, what happens is that a pair of particles -- basically, a particle and an anti-particle, or in other words, matter and anti-matter -- can appear spontaneously in a vacuum. They immediately annihilate each other, so conservation of mass and energy is maintained. But for that instant, it is not. And it is that violation of the second law of thermodynamics that allows a black hole to evaporate.

You see, over the course of billions of billions of years, such a pair of particles will appear billions of times next to the event horizon of a black hole. One of the pair will be swallowed by the black hole, and the other will radiate away from the black hole. The effect is such that the mass of the particle that escapes is actually reduced from the mass of the black hole. Over billions of billions of years, this process will reduce the mass of a black hole down to zero.

But, as Richard says, that process takes many, many times longer than the cosmos has already existed. So, a vast majority of black holes haven't lost all that much mass, and it will take many billions of times longer than the Universe has already existed for most black holes to evaporate in this fashion. And since there is little data to constrain the upper or lower limits of the spontaneous particle creation/annihilation, it's hard to set an exact date by which all the black holes in the Universe will evaporate.

So -- in the final analysis, it's something that happens. But it happens so slowly, relatively speaking, that we don't have to worry too much about it.

-the other Doug


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“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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ljk4-1
post Dec 8 2005, 02:14 PM
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--- Thursday, December 1, 2005 ---

===================================

** Perseus Cluster: Chandra Proves Black Hole Influence is Far Reaching

Scientists using NASA's Chandra X-ray Observatory have discovered
evidence of energetic plumes - particles that extend 300,000 light years
into a massive cluster of galaxies. The plumes are due to explosive
venting from the vicinity of a supermassive black hole, and they provide
dramatic new evidence of the influence a black hole can have over
intergalactic distances.

< http://chandra.harvard.edu/photo/2005/perseus/ >


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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Guest_Richard Trigaux_*
post Dec 8 2005, 02:14 PM
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QUOTE (dvandorn @ Dec 8 2005, 01:52 PM)
Mind?  Of course not!  That's what we do here.

By the way, I did a bit of research and got an explanation for the evaporation of black holes.  It seems that there is a phenomenon known to exist in the cosmos called "vacuum fluctuations."  ....

-the other Doug
*



Yes it is.

An interesting thing is that, after many theories, very small black holes would appear at time of a very violent collision between two particles, either from cosmic rays or into particle accelerators. But such micro-black holes, being very small, disintegrate instantly.

What would be interesting would be to observe this phenomenon in particule accelerators. because at the time when the micro-black hole disintegrates, all what was "inside" gets out again. So it is an unique mean to obtain information from within a black hole, and it could reply to many questions about what happen into black holes:

-are the particules swallowed by the black hole still existing individually, or are-they reduced to a singularity? (mar, a singularity is not a "thing" or an object, it is a point, in the mathematical meaning of this word, where common laws are no more valid. Think to a rubber membrane that you push with a nail, without however punching through: the point at the tip of the nail has special geometrical properties, that you can discover if you try to draw lines, squares, triangles, etc... on the membrane around it).

The alternative to a complete singularity would be some very compressed state of matter having in gross the diametre allowed by he Heisenberg uncertainties. (Mar, the Heisenberg uncertainties are, after quantum theory, a fundamental limit on the knowledge we can have of the position or energy of a particle. Within this domain, the particle appears as something blurred). But in this case, there would be a very small domain into the black hole with a normal physics, normal causality law and normal flow of time.

-Is the physics into a black hole similar tou ours, or may a new physics appear, eventually different for each black hole?


I would add that Hawking certainly has answers to all these questions, but very few people can judge of the validity of his work today, and no physical experiment can be designed to test his theories, except the one above.
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Marcel
post Dec 8 2005, 02:30 PM
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QUOTE (dvandorn @ Dec 8 2005, 01:52 PM)
But, as Richard says, that process takes many, many times longer than the cosmos has already existed.  So, a vast majority of black holes haven't lost all that much mass, and it will take many billions of times longer than the Universe has already existed for most black holes to evaporate in this fashion.  And since there is little data to constrain the upper or lower limits of the spontaneous particle creation/annihilation, it's hard to set an exact date by which all the black holes in the Universe will evaporate.

So -- in the final analysis, it's something that happens.  But it happens so slowly, relatively speaking, that we don't have to worry too much about it.

-the other Doug
*

As far as i know, singularities can exist in a variety of "sizes" and the time it takes for a black hole to evaporate by means of "Hawkins radiation (particles, antiparticles and gamma radiation) depends on it's mass. The lighter a black hole is, the faster it evaporates. Black holes that reside in galaxies (the 1 billion solar mass ones) theoretically take 10 to the 73 years to evaporate. However, there's theoretical evidence that smaller black holes (even as tiny as the Planck length) exist as well and they evaporate in very short times (instantly that is).

A question that keeps me curious about this theory is: if there's radiation coming from a black hole in the form of particles, antiparticles and gamma radiation (which has a speed of 300000 kms/hour), there must be other forms of radiation (the long searched gravity waves that is thought to escape from neutronstar-pairs ?) that can make its way from the event horizon. Why should gamma radiation make it, while other wavelengths cannot ?

Great explanation "other Doug' !
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Guest_Richard Trigaux_*
post Dec 8 2005, 03:31 PM
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QUOTE (Marcel @ Dec 8 2005, 02:30 PM)
As far as i know, singularities can exist in a variety of "sizes" ...
*


No, the singularity itself has no size; it is just a point (if singularities exist, there is no evidence of this). But it has a mass, and around it, a zone from where no information can come, so that from far it looks like a completelly black sphere. This sphere is called the event horizon, as nothing can be seen beyond. For a star sized black hole, its diametre is about some kilometres.

Yes, gravitation waves can come from a black hole, but only in the case when it is disturbed by a shock, for instance when two black holes merge to make only one: the resulting black hole vibrates and emits gravitation waves, until it dissipates its vibration energy and cease emitting, exactly like a guitar chord.


You meant 10 power 73 years, an amazing number indeed.
1000000000000000000000000000000000000000000000000000000000000000000000000 years.

A rotating black hole can also make rotate surrounding objects. A relevant analogy (not only an analogy, there are common mathematical laws) is with a transformer: the primary current creates a secondary current. So that a rotating black hole tugs the surrounding space. And, very like much in a transformer, the phenomenon is reversible: the matter outside the black hole can brake it, or in some instances accelerate it.
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ljk4-1
post Dec 8 2005, 03:40 PM
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Paper: astro-ph/0512194

Date: Wed, 7 Dec 2005 15:53:31 GMT (29kb)

Title: Constraints on Alternatives to Supermassive Black Holes

Authors: M. Coleman Miller (University of Maryland)

Comments: 5 pages including 1 figure, accepted by MNRAS
\\
Observations of the centers of galaxies continue to evolve, and it is useful
to take a fresh look at the constraints that exist on alternatives to
supermassive black holes at their centers. We discuss constraints complementary
to those of Maoz (1998) and demonstrate that an extremely wide range of other
possibilities can be excluded. In particular, we present the new argument that
for the velocity dispersions inferred for many galactic nuclei, even binaries
made of point masses cannot stave off core collapse because hard binaries are
so tight that they merge via emission of gravitational radiation before they
can engage in three-body or four-body interactions. We also show that under
these conditions core collapse leads inevitably to runaway growth of a central
black hole with a significant fraction of the initial mass, regardless of the
masses of the individual stars. For clusters of noninteracting low-mass objects
(from low-mass stars to elementary particles), relaxation of stars and compact
objects that pass inside the dark region will be accelerated by interactions
with the dark mass. If the dark region is instead a self-supported object such
as a fermion ball, then if stellar-mass black holes exist they will collide
with the object, settle, and consume it. The net result is that the keyhole
through which alternatives to supermassive black holes must pass is
substantially smaller and more contrived than it was even a few years ago.

\\ ( http://arXiv.org/abs/astro-ph/0512194 , 29kb)


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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maryalien
post Dec 10 2005, 01:18 PM
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QUOTE (Marcel @ Dec 8 2005, 02:30 PM)
As far as i know, singularities can exist in a variety of "sizes" and the time it takes for a black hole to evaporate by means of "Hawkins radiation (particles, antiparticles and gamma radiation) depends on it's mass. The lighter a black hole is, the faster it evaporates. Black holes that reside in galaxies (the 1 billion solar mass ones) theoretically take 10 to the 73 years to evaporate. However, there's theoretical evidence that smaller black holes (even as tiny as the Planck length) exist as well and they evaporate in very short times (instantly that is).

A question that keeps me curious about this theory is: if there's radiation coming from a black hole in the form of particles, antiparticles and gamma radiation (which has a speed of 300000 kms/hour), there must be other forms of radiation (the long searched gravity waves that is thought to escape from neutronstar-pairs ?) that can make its way from the event horizon. Why should gamma radiation make it, while other wavelengths cannot ?

Great explanation "other Doug' !
*


wasnt there a nasa presentation about GRB's and solving their mystery? i saw it in another forum but couldnt find an update as of yet. does this tie in? mar
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ljk4-1
post Dec 12 2005, 03:54 PM
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Paper: astro-ph/0512241

Date: Fri, 9 Dec 2005 06:09:19 GMT (23kb)

Title: Capture of a Red Giant by the Black Hole Sgr A* as a Possible Origin for
the TeV Gamma-Rays from the Galactic Center

Authors: Y. Lu, K.S. Cheng & Y.F. Huang

Comments: 15 pages, 1 figure, Accepted to ApJ
\\
Non-thermal TeV $\gamma$-ray emission within multi-pc scale has been observed
from the center region of our galaxy. We argue that these $\gamma$-rays are the
result of a transient activity of the massive black hole Sgr A$^*$ which
resides at the Galactic center. About thousands of years ago, the black hole
may have experienced an active phase by capturing a red giant star and forming
an accretion disk, temporarily behaving like an active galactic nuclear. A
powerful jet, which contains plenty of high speed protons, was launched during
the process. These runaway protons interact with the dense ambient medium,
producing TeV $\gamma$-ray emission through the $\pi^\circ$-decay process. We
show that the total energy deposited in this way is large enough to account for
observations. The diffusion length of protons is also consistent with the
observed size of the TeV source.

\\ ( http://arXiv.org/abs/astro-ph/0512241 , 23kb)


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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