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Offline syhprum

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Mini black holes
« on: 30/09/2006 17:39:56 »
If there was a 'small' black hole with the mass of the Earth nearby it would presumably be eveporating at an ever increasing rate, how close would it have to be for its radiation to be detectable and how long would we have left before it destroyed us

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Re: Mini black holes
« Reply #1 on: 30/09/2006 19:09:26 »
Would not whether it was evaporating would have to depend upon how much mass was falling into it, and whether the mass falling in balanced the Hawkin's radiation emitted by it.

As to whether it destroyed us - aside for the intensity of the Hawkin's radiation, and the radiation emitted by matter falling into the black hole (which would all be from day 1), why would you think it would destroy us?

If you are concerned that we may fall into the black hole, if the black hole has the same mass as the Earth, it will have the same gravitational pull as any Earth sized planet, and the likelihood that we would fall into it is the same as the likelihood that we would collide with a planet of similar size and in a similar orbit.




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Offline syhprum

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Re: Mini black holes
« Reply #2 on: 30/09/2006 20:09:09 »
I understand the smaller a black hole is the more rapidly it evaporates (I have heard that real mini's produced at CERN will have a life of 10^-24 seconds but 10 solar mass ones created at the 'Big bang' will be virtualy unchanged by now.
There must be a time when when one gets less and less massive and produces more and more radiation, I wondered when that point was reached and its rate of evaporation was significent on a human scale.


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Offline syhprum

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Re: Mini black holes
« Reply #3 on: 30/09/2006 20:31:05 »
I am assured by this article                     http://xaonon.dyndns.org/hawking/                                         that an Earth mass black hole would pose no danger as its effective temperature would be less than 2.7K but one of 10^5 Kg would only have a life of one second a would go off with a 5*10^6 megaton bang

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Offline Soul Surfer

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Re: Mini black holes
« Reply #4 on: 01/10/2006 11:02:25 »
That is a totally brilliant page syhprum.  I have been searching for ages for a page like that! I gives you the real scale of black hole behaviour.  It is interesting to note that a earth mass black hole is a bit less than 1 cm across, is much cooler than the background radiation and would therefore still grow slowly by absorbing that even in the absence of other material and would take more than  10^40 times the current age of the universe to evaporate assuming that the surroundings were much cooler than the current microwave background.

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Offline syhprum

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Re: Mini black holes
« Reply #5 on: 01/10/2006 13:06:23 »
I was surprised by the long life and small size that a Earth mass black hole would have, I am curious to know what the result of the collision of such an object and the Earth would be.
It is obvious that a great deal of energy would be liberated due to the kinetic energy of the collision but what would the long term result be.
Would it eventually settle at the center of the Earth, then would this be a stable state of affairs or would there be a collapse into a twice Earth mass black hole.
When it was first suggested that the latest generation of particle accelerators would produce micro mini black holes it was thought that they might be source of danger until their short life was pointed out but how an Earth mass one would behave I don't know.



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Offline syhprum

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Re: Mini black holes
« Reply #6 on: 01/10/2006 17:56:20 »
I have been busy creating blackholes (it's fun being a super being!) , I wanted one with the same energy output as the Sun (4.26 megatons/sec) so I created one of 0.1413 megatons but I am told it will have a life of about 7.52 years!!.
These figures do not add up, where did I go wrong?

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Offline Soul Surfer

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Re: Mini black holes
« Reply #7 on: 01/10/2006 23:53:30 »
You are asking for too much power output.  You also have your units wrong. A true solar energy one only lasts about 70 nanoseconds  and weighs about a metric ton.  If you chose a power output of 100,000 megawatts  (that is 50 large coal fired power stations enough to run a modest country)  It weighs about 50 million metric tons and lasts  500 million years but is still smaller than a typical atom!

The megatons output refers to megatons of TNT as in nuclear explosions. The sun's output is the conversion of about 4 million tons of mass into energy per second a very much bigger quantity.  The sun's output is about one hundred thousand megatons per second.

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Offline syhprum

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Re: Mini black holes
« Reply #8 on: 02/10/2006 09:45:17 »
I was in fact asking for too little power output I thought that the units 'megatons' refereed to actual mass of radiant energy not 'Tons of TNT' (there should be a law against using non S.I units) when I specify the output power in Watts I get a more sensible result.
I am now in a position to answer the original question that I asked but of course the nearby black hole must be much less massive than one Earth mass that I suggested to be anywhere near approaching the end of its life.
These caculations certianly destroy the theory that the Tungsaka event was caused by a black hole, one that caused that amount of damage could not lived long enough to have reached the Earth.



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Offline Soul Surfer

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Re: Mini black holes
« Reply #9 on: 02/10/2006 11:40:47 »
I should have said, you are asking for too much power output for  a long lived energy source from a black hole.  I therefore suggested one that could be put in a "box" and used as a generator.

I have been looking at the smallest black hole that you might be able to get inside withut being torn apart by the tidal forces.

If you allow about an earth gravity per metre tidal force.  that's likely to be uncomfortable but not destructive you find that the hole weighs about 30,000 solar masses and is about as big a Jupiter.

The probable reason that the really big ones go relatively quiet is that they get big enough for whole stars to get inside them without being torn apart by the gravity gradient.

I feel that there must be a second sort of event horizon inside the normal event horizon of a black hole.  That is, an upper value on the gravitational gradient.  It is the gravity gradient that creates the Hawking radiation and as the material inside the black hole contracts further towards the hypothetical singularity it will generate hawking radiation that will eventually of course fall back on to the hole but there is a time delay between the radiation of the energy and its return to the centre (this can be calulated and can be longer the bigger the hole gets)

As the material contracts so the radiation will get stronger and sap the energy of the cenral mass quicker. evenually there will be a balance between the mass in the centre and the radiation in transit.  All this should be calculable using classical physics  and I am not sure why no one has suggested it as a way out of this contraction to a mathematical singularity problem which as a physicist I find totally unacceptable  we live in a physical world of extended space and time not a mathematical one where infinitely small points exist

OK at these enormous energies the laws of physics will be stretched and bent by uncertainty  ans we get the conditions by which the laws of physics may have evolved

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Re: Mini black holes
« Reply #9 on: 02/10/2006 11:40:47 »

 

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