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ghhernandez
2007-Sep-04, 02:10 PM
Hi folks my first time on this or any INTERNET bd.... pray all is well with every one and their loved ones... my question involves black holes.... initially they just gobbled up energy and matter and kept them inside ... Hawkings has determined to everybody's satisfaction that black holes radiate energy and eventually dissapate...my question is...can a black hole radiate enough energy to allow that space in the universe not to be a black hole and allow the rest of the mass and energy thats left in the initial black to escape all at once?.. like a big bang of sorts....

Sp1ke
2007-Sep-04, 02:27 PM
I think it would be a gradual leakage until there was nothing left, rather than a big bang. Think of the Hawking radiation like a tiny hole in a tyre. The air slowly leaks out until the tyre's fully deflated.

And for any decent-sized black holes, they'll take a loooong time to evaporate. It's only the quantum-sized holes that evaporate quickly and they don't have enough oomph to make a pop, let alone a big bang.

Tim Thompson
2007-Sep-04, 03:17 PM
Hi folks my first time on this or any INTERNET bd ...
Welcome aboard


... my question is ... can a black hole radiate enough energy to allow that space in the universe not to be a black hole and allow the rest of the mass and energy thats left in the initial black to escape all at once? ... like a big bang of sorts ...
Yes & no. Yes, a black hole can radiate all of its energy at once, if it is small enough. But no, it won't look like the big bang, but it could be a fair imitation. There was a theory put forward by the same Stephen Hawking that primordial black holes (http://en.wikipedia.org/wiki/Primordial_black_hole), created during the big bang, would have a lifetime roughly the same as the current age of the universe. So those black holes, if they existed, and if any were still around, should be at the end of their lifetime against Hawking radiation, and their final demise could be an explanation for gamma ray bursts (GRBs). But we now have better explanations for GRBs, and the primordial black hole explanation has other problems.

The effective temperature of a black hole (in Kelvins) is roughly 10-7/M, where M is the mass of the black hole in solar masses. The lifetime of a black hole against Hawking radiation (in years) is about 1062M3, where M again is in solar masses. In order to have a lifetime less than about 10,000,000,000 years, a black hole must have a mass no greater than about 1013 kilograms, which is roughly 10-10 lunar masses, and 10-5 of the total mass of the atmosphere of Earth. But much of that mass will have evaporated away already by the time of the final burst. Still, that much mass turned into energy (E=MC2) will result in a very respectable bang, but more of a little bang, like a GRB, than the original Big Bang.

Sp1ke
2007-Sep-05, 08:59 AM
and their final demise could be an explanation for gamma ray bursts (GRBs)

Tim, is there actually a catastrophic end to a black hole? My simplistic understanding was that Hawking radiation allowed the energy of the BH to be gradually emitted so what triggers a large release of energy?

pilgrim
2007-Sep-05, 09:42 AM
Just wondring about something, how is Hawking radiation reconciled to the concept of a white hole? (or is it?) I mean, my understanding of a white hole was that the mass of the black hole 'falls out' of the white hole. But if all the mass of a black hole is leaked through Hawking radiation then there is no mass to fall out of a white hole. So technically they couldn't happen. Any thoughts? Or links to previous threads on the topic?

cjl
2007-Sep-05, 02:59 PM
Tim, is there actually a catastrophic end to a black hole? My simplistic understanding was that Hawking radiation allowed the energy of the BH to be gradually emitted so what triggers a large release of energy?
The reason is because the smaller the black hole gets, the faster the black hole radiates, and when it is extremely small, it has an extremely high effective temperature, radiating all its remaining energy and mass in a very short time.

Tim Thompson
2007-Sep-05, 03:04 PM
Tim, is there actually a catastrophic end to a black hole?
Yes. The temperature & lifetime formulas I gave previously (and have edited to fix a mistake in the temperature) are approximations that give incorrect results for very small black holes. For instance, a 1015 gram (5x10-19 solar masses) mass black hole comes out with a lifetime of 1062x(5x10-19)3 = 12,500,000 years, but a temperature of 10-7/5x10-19 = 2x1011 Kelvins, which don't make much sense together. But the real point of the exercise is that no matter how you cut it, as the mass goes down, the effective temperature goes way up fast, and the lifetime actually plummets accordingly. So at the end of its life, a microscopic black hole, with say the mass of a mountain or so, will disrupt itself violently by Hawking radiation, as an extremely high temperature burst.

See Communications in Mathematical Physics, vol. 43 no. 3 (http://projecteuclid.org/DPubS?service=UI&version=1.0&verb=Display&page=toc&handle=euclid.cmp/1103899179), and download the PDF of Stephen Hawking's paper Particle creation by black holes (the abstract button gave me broken-code gibberish, but the PDF should be available to anybody). This paper is linked from the Wikipedia page.

Sp1ke
2007-Sep-06, 08:58 AM
Thanks, Tim & cjl. I've got the PDF now so I'll start wading through it.

William
2007-Sep-06, 04:08 PM
There is a fair amount of new and unresolved science concerning Black Holes in general and in specific Hawking's Radiation. Hawking's radiation is based on the classical Black hole model which appears based on observations to be incorrect.

From observations it appears either Hawking's radiation does not occur (something is incorrect with that theory) or small black holes cannot form.

Small black holes should produce a prodigious amount of unique spectrum radiation, during there last days, hours, and seconds. i.e. A kin to a super nova as the BH becomes smaller.

Some theoreticians thought gamma bursts could be the end of life of a small black hole. Anne Green's attached paper shows based on the observed spectrum and duration of gamma ray bursts, that gamma ray bursts can not have been produced by end of life small black holes.


Viability of Primordial Black Holes as Short period Gamma Burst, by Ann Green

http://arxiv.org/abs/astro-ph/0105253


If the PBH mass function has a significant finite width, as recent numerical simulations suggest, then it is not possible to produce a present day PBH evaporation rate comparable with the observed short period gamma-ray burst rate. This could also have implications for other attempts to detect evaporating PBHs.


The following are a series of papers that discuss the issue from the perspective as what are the implications to the cosmological models, if small primordial black holes did not form?

Implications of Failure to Detect Primordial Black Holes by Andrew Liddle and Anne Green

http://arxiv.org/pdf/gr-qc/9804034


Primordial black holes may form in the early Universe, for example from the collapse of large amplitude density perturbations predicted in some inflationary models. Light black holes undergo Hawking evaporation, the energy injection from which is constrained both at the epoch of nucleosynthesis and at the present. The failure as yet to unambiguously detect primordial black holes places important constraints. In this article, we are particularly concerned with the dependence of these constraints on the model for the complete cosmological history, from the time of formation to the present. Black holes presently give the strongest constraint on the spectral index n of density perturbations, though this constraint does require n to be constant over a very wide range of scales.


Primordial Black Holes do they exist?

http://arxiv.org/pdf/astro-ph/0511743


For since PBHs with a mass of 10^15 g would be producing photons with energy of order 100 MeV at the present epoch, the observational limit on the γ-ray background intensity at 100 MeV immediately implied that their density could not exceed 10^-8 times the critical density [142]. Not only did this render PBHs unlikely dark matter candidates, it also implied that there was little chance of detecting black hole explosions at the present epoch [146]

This issue may be resolved when the Large Hadron Collider starts operation next year. If small black holes exists, then the LHC should produce roughly 1 micro black hole per day.

http://arxiv.org/abs/hep-ph/0112061

Discovering New Physics in the Decays of Black Holes, by Greg Landsberg


If the scale of quantum gravity is near a TeV, the LHC will be producing one black hole (BH) about every second, thus qualifying as a BH factory. With the Hawking temperature of a few hundred GeV, these rapidly evaporating BHs may produce new, undiscovered particles with masses ~100 GeV. The probability of producing a heavy particle in the decay depends on its mass only weakly, in contrast with the exponentially suppressed direct production. Furthemore, BH decays with at least one prompt charged lepton or photon correspond to the final states with low background. Using the Higgs boson as an example, we show that it may be found at the LHC on the first day of its operation, even with incomplete detectors.