One of the most important predictions of Einstein's theory of General Relativity is the existence of black holes. The dynamics of these systems are not yet fully understood, but researchers from Queen Mary, University of London have now provided a rigorous way of determining the evolutionary stage of a black hole by analysing the region outside where matter cannot escape, the event horizon.

Dr Thomas Bäckdahl and Dr Juan A. Valiente Kroon at Queen Mary's School of Mathematical Sciences have developed a method based on properties of the Kerr solution, a time-independent solution to the equations of General Relativity.

The Kerr solution is one of the few exact solutions to the equations of General Relativity, and describes a rotating, stationary (time-independent) black hole. It is also proposed that it describes the final evolutionary stage of any dynamical (time-dependent) black hole.

General Relativity provides a unified description of gravity as a geometric property of space and time. The theory predicts the existence of black holes as regions in which the space and time are distorted so that nothing can escape them.

Dr Valiente Kroon, an EPSRC Advanced Research Fellow, said: "By looking at the region outside the black hole we have shown how to ascertain how much a dynamical black hole differs from the Kerr solution. There are very strong indications that the end state of the evolution of a black hole is described by this solution." The findings are reported in the journal *Proceedings of the Royal Society A*.

The ideas developed in the article may be of relevance in developing numerical simulations of black holes, an area of research that has experienced a great development in recent years. Due to the complexity of the equations of General Relativity, these simulations are the only way of systematically exploring the theory in realistic scenarios.

**Explore further:**
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**More information:**
The paper "The 'non-Kerrness' of domains of outer communication of black holes and exteriors of stars", Thomas Bäckdahl and Juan A. Valiente Kroon will appear in *Proceedings of the Royal Society A *on 19 January. arxiv.org/abs/1010.2421

## Moebius

## fmfbrestel

## axemaster

Correct!

Let me clear things up for you. Spacetime is a coordinate system. In addition, you should know the rule of inertia - an object will always travel in a straight line unless acted upon by a force.

Now combine the implications of proofs that show "relative time" being affected by both relative motion and by gravity. This strongly suggests that gravity is not a "force" per se.

Now, look at inertia again. Objects like to travel in straight lines. Therefore, if a beam of light is deflected around a gravitational object, that means that the light is still traveling in a straight line - the coordinate system is warped!

## lengould100

Opinions?

## Mr_Man

This makes perfect sense to me. But it also makes sense logically that you can't think of space time as having just a 3D property (X,Y & Z axis), there would have to be another dimension to allow light bent by gravity to still be considered moving along a "straight line" if space-time uses an X,Y and Z axis. This is also assuming that gravity isn't the result of a compressed area of space time, in which case you could get away with using the X,Y & Z axis to explain this.

## Mr_Man

Just to clarify, if we are thinking of space-time as being a coordinate system, and there is an X,Y & Z axis, then the extra dimension that I am referring to would cause the coordinate system to be a X,Y,Z & G system where the "G" dimension allows the warping of the X,Y,Z coordinates without actually compressing or expanding the "grid" where light is bent. We all know that gravity warps space-time but it seems to me that this would actually this would be considered another dimension.

## axemaster

I guess a better way might be to invoke the equivalence principle, which states that the gravitational force is the same as the "fake" force felt in an accelerating frame of reference (like an accelerating rocket). Basically doing that gives you:

(gravitational acceleration) x (gravitational mass) = (acceleration) x (inertial mass)

In other words, if you are standing on the ground, you are actually NOT motionless - you are in fact accelerating upwards at 9.8 m/s^2. The straight line trajectory of your body is bent inwards, so the ground must constantly bend it upwards.

It's hard to explain succinctly, I suggest you read up on it.

## Mr_Man

I've often thought of gravity as being the result of mass "displacing" space-time. I had a wild thought once of gravity working by matter displacing space-time so that it is compressed around the massive object. The compressed space-time is actually the gravitational field, the field is a result of a more "dense" region of space-time that gets exponentially denser as the gravity strengthens. If a particle functions as a probability wave (such as a photon or electron, and possible other particles), when it comes in contact with the compressed space-time it has a higher probability of "appearing" in the field. That probability increases exponentially the closer it gets to the source of the gravity since there is more space-time there. Objects are caught in a gravitational pull because of an average of probabilities. Its like playing slot machines a million times, you WILL lose.

## OregonWind

Nice book but keep in mind Moffat's ideas are still controversial.

## Mr_Man

## OregonWind

If you did not expect your idea to be "correct" by any means how then did you find it interesting?

## ekim

Any particle falling into a black hole will eventually contribute to this radiation in time.

Since black holes cause dilation of time, this conversion into radiation seems instantaneous to the particle.

An observer, positioned further away, would view this event as taking longer.

Why is an infinite singularity necessary?

## Moebius

I wasn't setting it up, I just know that people who consider themselves physicists do not like their values questioned and my opinion would get 1's from them. The book on time hasn't been written yet and its exact nature isn't known by anyone. Speculating on it is just as valid for a philosopher as it is a physicist. I happen to think that physicists haven't got it right. The fact that many of them think time travel is possible is proof. It goes back to my statement that infinity only exists in our minds. Time travel not only involves infinity, but an infinity of infinities. It is impossible for that reason alone, never mind the paradoxes. Time will tell who is right.

## Skeptic_Heretic

## ekim

Quantum physics seems to allow "spooky actions" seemingly violating the rules of space. Could this also be applied to the time dimension? Experiments involving "weak quantum measurements" seem to imply that time might not be a linear as it seems.

Time will tell.

## LarsKristensen

Relative time is therefore only a time resulting in an observation image and do not affect the observed and the actual physical time the observed find themselves in.

## 71STARS

Dead stars will abound in the Universe. But a dead star in the middle of the Milky Way or any galaxy should mean a mass of dead matter, shrinking to eventual nothingness. Nature lets nothing go to waste. Where is the energy in a dead star? What is giving it energy? Will all stars become a vortex and gain energy, with no light showing, but yet feeding on anything that comes in sight because it now has an enormous gravitational pull? What part of dead is not dead?

## eachus

When Sirius A becomes a red giant some of its mass will be drawn off by Sirius B. Given what we know the longer it takes Sirius A to become a red supergiant the more of its mass will be devoured by Sirius B. (Of course, some of that mass came from Sirius B to begin with.)

Worst case, Sirius B will become massive enough to become a Ia supernova. But don't worry about that, if it happens the sun will be a lot further away.

All that is interesting, but on the subject of distorted space time, Sirius B swims in it. With a large enough telescope you can see the distortion caused by Sirius B. Or you can just look at the spectral lines from Sirius B, they are red-shifted.

## Walter_Mrak

## Walter_Mrak

The most compelling truths and conversely, immature misappreciations of fact, can turn out to be valid depending upon many things. An infintessimally small "singularity" became and is now, an ever expanding universe. An "atom" is indivisible. Blah, Blah Blah. We can only strive for equations to make use of knowledge and in that knowledge take solace, but " will/can " never really understand or make sense of that knowledge completely. OOPS… Maybe we could if we were obsessive compulsive, focussed, and chose to devote enough time?!

## frajo

## Bob_Kob

Straw man.

## Walter_Mrak

## hush1

The 'frozen' part! :)

I like to imagine myself convincing you, after you have successfully thawed me out after a deep freeze, that I am still the same old me.

Everyone will notice I have sidestepped the 'physical' here at hand, and have taken refuge in the consciousness.

A subliminal cope out to express my desire to see the physical and consciousness as one.