Black Holes Serving as Particle Accelerator

A particle collision at the RHIC. No strangele...

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Black Hole Particle Accelerator!! Sounds so strange !! Well, this is not that much strange as it may purport. Particle accelerators are devices which are generally used to raise the particles at very high energy levels.

Beams of high-energy particles are useful for both fundamental and applied research in the sciences, and also in many technical and industrial fields unrelated to fundamental research. It has been estimated that there are approximately 26,000 accelerators worldwide. Of these, only about 1% are the research machines with energies above 1 GeV (that are the main focus of this article), about 44% are for radiotherapy, about 41% for ion implantation, about 9% for industrial processing and research, and about 4% for biomedical and other low-energy research.

For the most basic inquiries into the dynamics and structure of matter, space, and time, physicists seek the simplest kinds of interactions at the highest possible energies. These typically entail particle energies of many GeV, and the interactions of the simplest kinds of particles: leptons (e.g. electrons and positrons) and quarks for the matter, or photons and gluons for the field quanta. Since isolated quarks are experimentally unavailable due to color confinement, the simplest available experiments involve the interactions of, first, leptons with each other, and second, of leptons with nucleons, which are composed of quarks and gluons. To study the collisions of quarks with each other, scientists resort to collisions of nucleons, which at high energy may be usefully considered as essentially 2-body interactions of the quarks and gluons of which they are composed. Thus elementary particle physicists tend to use machines creating beams of electrons, positrons, protons, and anti-protons, interacting with each other or with the simplest nuclei (e.g., hydrogen or deuterium) at the highest possible energies, generally hundreds of GeV or more. Nuclear physicists and cosmologists may use beams of bare atomic nuclei, stripped of electrons, to investigate the structure, interactions, and properties of the nuclei themselves, and of condensed matter at extremely high temperatures and densities, such as might have occurred in the first moments of the Big Bang. These investigations often involve collisions of heavy nuclei – of atoms like iron or gold – at energies of several GeV per nucleon.

[Image Details: A typical Cyclotron]

In current we accelerate particles at high energy levels by increasing the kinetic  energy of a particle and applying a very high electromagnetic field. Particles are accelerated according to Lorentz Force. However there are some limitations of such particle accelerators like we can’t accelerate them at very high energy levels. It needs a lot of  distance to be covered up before acquiring a desired speed.

This can be simply accumulated from the astounding details of LHC. The precise circumference of the LHC accelerator is 26 659 m, with a total of 9300 magnets inside. Not only is the LHC the world’s largest particle accelerator, just one-eighth of its cryogenic distribution system would qualify as the world’s largest fridge. It can accelerate particles upto the energy level of 14.0 TeV.

As it is pretty obvious that to accelerate particles above this energy level it would become almost imposssible.

An advanced civilization with the development level of typeIII or type IV would more likely choose to implement black holes rather than engineering a LHC or Tevatron at astrophysical scale. Kaluza Klein black holes are excellent for this purpose. Kaluza Klein black holes are very similar to Kerr black holes except they are charged.

Kerr Black Holes

Kerr spacetime is the unique explicitly defined model of the gravitational field of a rotating star. The spacetime is fully revealed only when the star collapses, leaving a black hole — otherwise the bulk of the star blocks exploration. The qualitative character of Kerr spacetime depends on its mass and its rate of rotation, the most interesting case being when the rotation is slow. (If the rotation stops completely, Kerr spacetime reduces to Schwarzschild spacetime.)

The existence of black holes in our universe is generally accepted — by now it would be hard for astronomers to run the universe without them. Everyone knows that no light can escape from a black hole, but convincing evidence for their existence is provided their effect on their visible neighbors, as when an observable star behaves like one of a binary pair but no companion is visible.

Suppose that, travelling our spacecraft, we approach an isolated, slowly rotating black hole. It can then be observed as a black disk against the stars of the background sky. Explorers familiar with the Schwarzschild black holes will refuse to cross its boundary horizon. First of all, return trips through a horizon are never possible, and in the Schwarzschild case, there is a more immediate objection: after the passage, any material object will, in a fraction of a second, be devoured by a singularity in spacetime.

If we dare to penetrate the horizon of this Kerr black hole we will find … another horizon. Behind this, the singularity in spacetime now appears, not as a central focus, but as a ring — a circle of infinite gravitational forces. Fortunately, this ring singularity is not quite as dangerous as the Schwarzschild one — it is possible to avoid it and enter a new region of spacetime, by passing through either of two “throats” bounded by the ring (see The Big Picture).

In the new region, escape from the ring singularity is easy because the gravitational effect of the black hole is reversed — it now repels rather than attracts. As distance increases, this negative gravity weakens, just as on the positive side, until its effect becomes negligible.

A quick departure may be prudent, but will prevent discovery of something strange: the ring singularity is the outer equator of a spatial solid torus that is, quite simply, a time machine. Travelling within it, one can reach arbitrarily far back into the past of any entity inside the double horizons. In principle you can arrange a bridge game, with all four players being you yourself, at different ages. But there is no way to meet Julius Caesar or your (predeparture) childhood self since these lie on the other side of two impassable horizons.

This rough description is reasonably accurate within its limits, but its apparent completeness is deceptive. Kerr spacetime is vaster — and more symmetrical. Outside the horizons, it turns out that the model described above lacks a distant past, and, on the negative gravity side, a distant future. Harder to imagine are the deficiencies of the spacetime region between the two horizons. This region definitely does not resemble the Newtonian 3-spacebetween two bounding spheres, furnished with a clock to tell time. In it, space and time are turbulently mixed. Pebbles dropped experimentally there can simply vanish in finite time — and new objects can magically appear.

Recently, it was made an interesting observation that black holes can accelerate particles up to unlimited energies Ecm in the centre of mass frame. These results have been obtained for the Kerr metric (they were also extended to the extremal Kerr-Newman one. It was demonstrated that the effect in question exists in a generic black hole background (so a black hole can be surrounded by matter) provided a black hole is rotating. Thus, rotation seemed to be an essential part of the effect. It is also necessary that one of colliding particles have the angular momentum L1 = E1/ωH  where E is the energy, ωH is the angular velocity of a generic rotating black hole. If  ωH→0, L1 →1, so for any particles  with finite L the effect becomes impossible. Say, in the Schwarzschild space-time, the ratio Ecm/m (m is the mass of particles) is finite and cannot exceed 2√5 for particles coming from infinity.

Meanwhile, sometimes the role played by the angular momentum and rotation, is effectively modeled by the electric charge and potential in the spherically-symmetric space-times. So, one may ask the question: can we achieve the infinite acceleration without rotation, simply due to the presence of the electric charge? Apart from interest on its own., the positive answer would be also important in that spherically-symmetric space-times are usually much simpler and admit much more detailed investigation, mimicking relevant features of rotating space-times. In a research paper by Oleg B. Zaslavskii, they showed that centre of mass energy can reach reach up to very high level and may gain almost infinite centre of mass energy before collision. Following the analysis and energy equations ,the answer is ‘Yes!’ .
The similar conclusion were also extracted by Pu Zion Mao in a research paper ‘Kaluza-Klein Balck holes Serving as Particle Acclerator.
Consider two mass particles are falling into a black hole having angular momentum of L1 and L2.

Obviously, plot r  and centre of mass energy near horizon of Kaluza Klein Black Hole in Fig.1 and Fig.2, from which we can see that there exists a critical
angular momentum Lc = 2μ/√(1-ν²)  for the geodesics of particle to reach the horizon. If L > Lc, the geodesics never reach the horizon. On the other hand, if the angular momentum is too small, the particle will fall into the black hole and the CM energy for the collision is limited. However, when L1 or L2 takes the angular momentum L = 2μ/√(1-ν²) , the CM energy is unlimited with no restrictions on the angular momentum per unit mass J/M of the black hole.
Now, it seems very mesmerizing that advanced alien civilization would more likely prefer to implement black holes as particle accelerator. However, that implementation could be moderated.
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