Black Holes |
Black Holes |
Dec 7 2005, 04:04 PM
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#1
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Newbie Group: Members Posts: 8 Joined: 6-December 05 Member No.: 599 |
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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Dec 8 2005, 01:52 PM
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#2
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Senior Member Group: Members Posts: 3419 Joined: 9-February 04 From: Minneapolis, MN, USA Member No.: 15 |
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 -------------------- “The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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Dec 8 2005, 02:30 PM
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#3
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Member Group: Members Posts: 290 Joined: 26-March 04 From: Edam, The Netherlands Member No.: 65 |
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_* |
Dec 8 2005, 03:31 PM
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Guests |
QUOTE (Marcel @ Dec 8 2005, 02:30 PM) 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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Dec 8 2005, 03:40 PM
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
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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