Posted on 10/13/2008 12:28:52 AM PDT by LibWhacker
You can manipulate a black hole as much as you like but youll never get rid of its event horizon, a new study suggests. This may sound a little odd, the event horizon is what makes the black hole, well black. However, in the centre of a black hole, hidden deep inside the event horizon, is a singularity. A singularity is a mathematical consequence, it is also a point in space where the laws of physics do not apply. Mathematics also predicts that singularities can exist without an associated event horizon, but this means that wed be able to physically see a black holes singularity. This theoretical entity is known as a naked singularity and physicists are at a loss to explain what one would look like.
Like any good physics experiment, an international team from the US, Germany, Portugal and Mexico have decided to simulate the most extreme situation possible in the aim of stripping a pair of black holes of their event horizons. They did this by constructing an energetic collision between two black holes travelling close to the speed of light, crashing head-on. Heres what they discovered
Actually, Emanuele Berti (JPL/Caltech) and his collaborators didnt set out to embarrass a black hole; they were simulating some extreme collisions between two massive bodies, watching the ripples in space-time (gravitational waves) propagate. In this case, they were using the computer simulation (carried out by Uli Sperhake, who was working in Germany at the time and has since begun work at Caltech) to examine the gravitational waves generated when two black holes of equal mass were driven together, head-on, close to the speed of light. The two black holes then merged to form one large black hole.
The results from Sperhakes simulation were very interesting. Unlike previous simulations examining lower-energy collisions, far more energetic gravitational waves were produced. So much so that 14% of the total masses of the colliding black holes were converted into gravitational wave energy. So far so good. If this extreme (and unlikely) scenario were to occur, perhaps wed know what to look out for in the noisy LIGO data, and we might gain an estimate of how much mass black holes shed in these encounters. However, theres another outcome to this research: black holes keep their event horizons no matter what is thrown at them.
This may seem like an obvious outcome to this experiment, but it has some significant implications for how our Universe works. In 1969, mathematical physicist Roger Penrose conceived the cosmic censorship hypothesis which states that no naked singularities can exist in nature (apart from the Big Bang 13.73 billion years ago). A space-time singularity is the point at which the quantities used to measure the gravitational field become infinite (i.e. a large star collapses due to lack of fusion and the stellar matter is too massive to support itself; it collapses to a single point, creating the singularity inside a black hole). Because space-time becomes extremely warped in the vicinity around this gravitationally dominant point, a boundary surrounding the singularity called the event horizon will form, marking the distance from the singularity that even light cannot escape. Any light emitted inside the event horizon can never escape beyond this boundary; anything straying too close to the horizon risk falling into the boundary of the black hole, never to return.
The event horizon is what gives black holes their name. If no light travels beyond the event horizon, and only stuff can fall in, a black sphere remains in three dimensional space (with a radius dependent on the mass held in the singularity, see Schwarzschild radius). So, any gravitational singularity should be dressed with an event horizon. However, mathematics predicts that singularities can exist without an event horizon, thereby making them naked singularities.
This is where Penroses cosmic censorship hypothesis comes in. Our Universe must have some natural ability where an event horizon will always be associated with a singularity. It would seem this new research confirms the British professors 40 year-old theory that a black hole cannot be stripped of its event horizon, no matter how violently it is treated. This is fortunate, as modern physics has no way to describe what a naked singularity would look like.
We hope its true, Berti says of the cosmic censorship hypothesis, because it basically hides the failures of general relativity behind the event horizon.
It’s good for all of us that Helen Thomas is not a naked singularity.
Naked pairing is much better.
Silly physicists ... it would look like this below.
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Correct. But as the relative time approaches a standstill, the motion will get increasingly smaller and smaller, we should get something akin to Zeno’s paradoxes where you can never actually reach the point where time has stopped but simply creep toward that point mroe slowly and slowly.
Exactly. Unless the universe has infinite time, then the universe will end before the true singularity where time has stopped actually forms.
As I understood it, the mathematical point at which light cannot escape corresponds to the mathematical point where time effectively stops for matter. If that’s not the case, then that’s what I’d like to know.
“As I understood it, the mathematical point at which light cannot escape corresponds to the mathematical point where time effectively stops for matter. If thats not the case, then thats what Id like to know.”
No. We observe gravitational fields in relation to velocity but that’s not what is happening (according to the guys with higher IQs than me). The gravity field is so powerful, it is bending spacetime. Time is still moving at a slower rate to the outside observer (normal to the unlucky person in the event horizon) and the gravitational forces are tearing all mass apart. Read ‘Death by Black Hole’ by Neil deGrasse Tyson about spaghettification :)
At the point of singularity itself, time has reached zero.
http://en.wikipedia.org/wiki/Gravitational_singularity
Read Types - Curvature for the mathematics about it.
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Yes, and if time has stopped at the singularity, it’s nearly stopped just outside of the singularity so how does anything actually ever reach the singularity?
Yes. That is the theory.
Thanks, I read it, and now my head hurts!
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