deano

imagine you had the power to re arrange black holes themselves.
and with this power you would re arrange a number of black holes in a geometric way,in such a formation that their gravitational pulls battle for dominance but are not close enough to be swallowed by each others event horizons.

would the black holes start to orbit each other?,or move in a set pattern.i know black holes have an intrinsic spin but i doubt they move from their fixed points due to their immense gravity.

now if they were to "orbit" each other, they would accelerate at an ever increasing pace.eventualy they themselves approach the speed of light!

now this is what im interested in,WHAT WOULD HAPPEN TO BLACK HOLES IF THEY MOVED AT THE SPEED OF LIGHT???.

special relativity,do your work!

Shadowy Man

Well, I doubt you'd have enough energy available to speed orbiting black holes up to the speed of light.

Most likely, orbiting black holes would act like the orbiting pulsars that have been seen. They would emit gravitational waves, causing the orbiting black holes to spiral in towards each other until they coalesced.

Lobstrosity

Wait, why would orbiting black holes accelerate to near the speed of light? Shadowy Man is right, the black holes would lose energy in the form of gravitational waves, thereby spiraling into each other. Also, as a massive object, black holes cannot actually move at the speed of light. They can move at near the speed of light, but that's not really all that special. After all, relativity tells us that all inertial reference frames are equivalent under Lorentzian transformations, meaning that a black hole moving at near the speed of light is isomorphic with the situation where you are moving at near the speed of light and the black hole is stationary.

deano

ah yes.

i assumed because black holes have near infinite gravity,they would have near infinite acceleration over a period of time due to so much potential energy.

i dont have a physics education so i was unaware of gravational waves.

what are they?,gravitons?

how do black holes emit gravitational waves?,i know they emit radiation.

i want to know how a singularity would act at speeds approaching the speed of light to.

teach me!

Shadowy Man

They don't have near infinite gravity. They have a finite mass, therefore they have a finite gravitational affect on things. If you are outside of a black hole's event horizon (and also outside of its ergosphere, but that's another matter) then you are attracted to it just as you would any other object of its mass - though the tidal forces may be more extreme if you are close enough.

The theory of relativity predicts that masses being accelerated should emit gravitational radiation in the same way that charged particles (like electrons) emit electromagnetic radiation when they are accelerated.

Though gravitational radiation has not been directly observed (there are currently a few experiments being set up to look for it) it has been inferred from the observations of orbiting pulsars - Hulse and Taylor won the Nobel Prize for Physics in 1993 for just such an observation.

Lobstrosity

Well, a black hole would have near infinite gravity if you're almost infinitesimally close to the singularity, but then again an electron has near infinite gravity if you get close enough, also (well, if the whole point-particle concept of elementary particles is correct, which it certainly may not be). The thing to note is that this near infinite gravity only exists well within the event horizon in a regime that is completely isolated from the rest of the physical universe. The two black holes will have "coalesced" by that point.

Gravitational waves are a consequence of general relativity--they can be seen to arise from the equations of the theory itself. You can either think of them as streams of gravitons (the particle version) or of distortions of the fabric of space itself (the wave version) that propagate out to infinity. They are analagous to the electromagnetic radiation produced by accelerating charges. In short, an accelerating charge radiates photons; this is both theoretically predicted by the equations of electrodynamics and empirically verified. In much the same way, GR predicts that accelerating masses will radiate gravitons. Gravitational waves have never been directly detected as far as I know, but there are projects underway to do just that. Here is an article about one of them. I can explain to you mathematically why accelerating charges radiate, however I do not know enough GR to do the same for accelerating masses.

Edit: I know, I know, I basically just said verbatim what Shadowy Man said, but hey, I took the time to type it (too much time, it seems) and as such I'm damn well going to post it...damnit!

deano

ah.

an event horizon is the point from where nothing can escape,but there is still gravatational force outside of it?

so when a particle is accelerated it emits energy in the form of electromagnetic radiation,is this what is known as energy conservation??.

when a particle emits gravitons or whatever,does the overall affect of all particles together each affecting space time a bit,warp space time to the extent that we have gravity as shown by special relativity where gravity is essentialy warped space?.

also im aware that when a particle does emit electromagnetic radiation it looses some of its mass,is this mass lost through/transfered to the gravatational waves themselves but in a energy form??

Lobstrosity

Fields exist outside of a black hole. It still produces a gravitational field and if it has a net charge it will produce an electric field. Gravitational fields represent the warping of space due to the presence of mass, not an escaping signal.

Well, energy is conserved (as always), but this is not known as energy conservation. In fact, most people are probably completely oblivious to the fact that accelerating charges radiate, even though it's responsible for a lot of phenomena we encounter ever day (e.g. the fact that the sky is blue).

I don't think I know what you're asking. Perhaps I'll leave this to Shadowy Man.

No, an accelerating charge does not lose any mass when it emits electromagnetic radiation. The energy for the radiation comes at the expense of the particle's kinetic energy, not its mass. The radation provides what is known as a radiation reaction force that opposes the direction of motion. The same thing would happen to accelerating masses--they would convert kinetic energy into gravitational energy (gravitons). This is why the black holes would spiral into each other: the loss of kinetic energy would also be a loss of angular momentum, which in turn would result in a decrease of orbital radius.

Walross

Originally posted by Lobstrosity:

Hmm, I don't mean to confuse matters or derail this thread, but I thought that the sky was blue because the blue part of the spectrum scattered more readily off the atmosphere. I could, of course, be wrong about that. Regards,

Walross

Lobstrosity

To quote Griffiths' Introduction to Electrodynamics, Third Edition, page 449:

• The sharp frequency dependence of the power formula (Eq 11.22) is what accounts for the blueness of the sky. Sunlight passing through the atmosphere stimulates atoms to oscillate as tiny dipoles. The incident solar radiation covers a broad range of frequencies (white light), but the energy absorbed and reradeated by the atmospheric dipoles is stronger at high frequencies because of the &#969&#8308 in Eq 11.22. It is more intense in the blue then, than in the red. It is this reradiated light that you see when you look up in the sky--unless, of course, you're staring directly at the sun.
  
  Because electromagnetic waves are transverse, the dipoles oscillate in a plane orthogonal to the sun's rays. In the celestial arc perpendicular to these rays, where the blueness is most pronounced, the dipoles oscillating along the line of sight send no radiation to the observer; the light received at this angle is therefore polarized perpendicular to the sun's rays.

Eq 11.22: <P> = &#956p²&#969&#8308/(12&#960c)

This equation gives the time-averaged power radiated by an oscillating electric dipole of maximum magnitude p as a function of frequency &#969 (in SI units).

Dipole radiation arises from the acceleration of charge within tiny dipoles and is the reason why the light from certain regions of the sky is polarized--you may have noticed this if you were ever playing around with polarizers or polarized glasses.