Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Soul Surfer on 06/01/2009 20:20:10
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The only really interesting sorts of black holes are those that rotate because it is virtually impossible to create one that isn't rotating.
Now this rotational energy has a maximum value for a given mass of black hole.
Does anyone know what the maximal rotational energy of a given mass of black hole is, how this value varies as the total mass of the black hole gets larger and how this compares with the gravitational mass energy of the black hole?
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I have done a bit of searching one reference suggests that the rotational energy can equal the mass energy of the hole.
Another suggests that all the rotational energy can be extracted and it is not inside the event horizon and this can amount to 29% of the mass energy of the hole.
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Now this rotational energy gas a maximum value for a given mass of black hole.
Is this because if it's spinning too fast the gravity won't be enough to suck it all into a black hole?
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If we wanted to measure the rotational speed of a blackhole how could we go about it ?
It seems a none starter to me.
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I think it should be possible to detect some of the effects of frame-dragging from outside the EH.
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Yep, that's how they're counted:)
Frame dragging is so cool:)
" We can detect neutron stars because of three things...
1.Much of the star’s angular momentum remains, but with the small diameter this means that the star rotates at high speed - perhaps 30 times/second.
2. Neutron stars have high magnetic fields that are not aligned with their axis of rotation. This means their magnetic fields sweep through their local space as the star rotates.
3.They collect charged particles.
The high magnetic field sweeping past the charged particle streams causes synchrotron radiation at X-ray wavelengths.
So if the magnetic axis sweeps through the direction in which the Earth lies we will detect a radiative source pulsing once per revolution at perhaps 30 beats a second - a very distinctive stellar signature! "
Spinning Black holes creates a frame dragged 'accretion' disk of dust and gas outside its event horizon as materials tries to 'fall in'.
Then the magnetic fields help the (also spinning) accretion disk to flow 'down' towards the black holes event horizon.
Which then 'reacts' by launching 'Jets' of low density materials from the 'top and the 'bottom' of that spinning black hole.
That will will send charged particles out in space that we can measure (as I understands it).
http://www.mariner.connectfree.co.uk/Gravity/Extreme_gravity/extreme_gravity.html
http://www.newscientist.com/article/dn13183-photons-orbit-black-hole-roulette-wheel.html
http://en.wikipedia.org/wiki/Frame-dragging
http://www.bu.edu/blazars/songs/superluminallover.html
http://en.wikipedia.org/wiki/Gravity_Probe_B
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I'm not sure if there is any way to be able to measure this, there probably isn't.
However, if a black hole was magnetized and there was a strong enough magnet in the area stuff could come out and you could make calculations but that is something that would cost trillions of dollars and would require a lot of tools we don't have I'm sure. Anyway that's the only way to take matter of a black hole that I can think of
however, we can make some very good calculations based on our experiences with "normal" matter.
well in any case I'm not sure if there can be a maximum, but it's possible that after a certain point this kinetic energy will turn into mass.
Other than that since by definition the escape velocity of a black hole is greater than the speed of light which isn't possible to achieve objects going in could be going infinitely close to the speed of light and probably almost all of them are at least .9 c anyway.
Therefore I doubt there can be any limit to the velocity of the particles rotating around the black hole which in turn would mean that the maximum rotational energy of the black hole would be equal to one half of the mass of the black hole*the square of the speed of light (the maximum velocity of the mass inside) this is given by the kinetic energy formula KE=1/2 mv^2 and e=mc^2
which supports what you found though I believe the one have should be in there it's hard to know what happens as objects approach the speed of light and I'm not versed in that kind of thing
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also you could use the energy of rotation formula K=1/2(l)(omega)^2 and using I=(2/5)*mr^2 and use the mass and finding the radius would prove to be a trick but if you know what you're doing you'll know that the units omega or the rate of rotation in radians is the inverse of the radius squared and all you are left with is 1/2mv^2 or just plugging in numbers will give you the same answer with the 1/2
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However, if a black hole was magnetized and there was a strong enough magnet in the area stuff could come out and you could make calculations but that is something that would cost trillions of dollars and would require a lot of tools we don't have I'm sure. Anyway that's the only way to take matter of a black hole that I can think of
You couldn't suck matter from the inside the event horizon of a black hole out with a magnet. Even another black hole wouldn't do that.
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Ryth :) the only thing you would reach with a 'super magnet' would be stuff outside the Event horizon.
A 'event horizon' is the beginning of a gravity well so deep that light passing it can't turn back (think mirror:)
All light reflected inside a spinning black hole has only one way and that's down.
As for a super massive black hole meeting a more 'normal sized' Black hole I will have to trust what Madidus wrote.
But it is a very interesting thought though.
As there exist bigger and smaller infinity's defined in mathematics?
Can there be bigger and smaller 'singularitys forces' in spacetime?
And if there was, would it matter :)
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Well, a maximal rotating black hole would be one that is rotating at light speed.
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Ryth :) the only thing you would reach with a 'super magnet' would be stuff outside the Event horizon.
A 'event horizon' is the beginning of a gravity well so deep that light passing it can't turn back (think mirror:)
All light reflected inside a spinning black hole has only one way and that's down.
As for a super massive black hole meeting a more 'normal sized' Black hole I will have to trust what Madidus wrote.
But it is a very interesting thought though.
As there exist bigger and smaller infinity's defined in mathematics?
Can there be bigger and smaller 'singularitys forces' in spacetime?
And if there was, would it matter :)
Mathematically speaking, i do believe there can be bigger and smaller infinite singularities in spacetime.
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Well, a maximal rotating black hole would be one that is rotating at light speed.
Here i mean, even a black hole can be subject to rotating at the speed of light, which means its rotational energy would be due to such limited bounds. Calculating it should be too hard.
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Interesting mr S.
Still, nothing can reach 'c' if made of matter, right?
But it can come very near.
So it's a time machine of sorts then:)
How will 'the charge' of the magnetic field(s?) spin?
Around the BH or only at the 'poles' sort of.
To me it seems that it should be a 'whole' spinning.
But if one takes a sphere, can one say that it has any 'ends' sticking out?
As well as saying that this is the 'middle' of its 'body'
The 'middle' of that EV would only be a relation defined by the Black Holes spinning, right.
The BH should deliver a equal framedragging over the whole 'sphere' of the event horizon.
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Or should it?
What I mean here is that the angular momentum (?) seen at the thought middle line of that event horizon, in the direction of the Black Holes spin, should be stronger there than on its sides.
Creating a lag around that 'middle line' geometrically seen?
possibly with 'child vortexes' being created around it as a result?
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I'm not sure how that frame dragging would express itself?