Energy From Black Hole?


Energy From Black Hole?

Black holes are believed to be responsible for a number of highly energy astrophysical phenomena from active galactic nuclei to gamma ray burst to ultra luminous X-rays binaries. There may be two different regions for the extraordinary amount of energy released during such events. These two different regions may be gravitational collapse or gravitational potential energy of matter falling toward an existing or forming black hole during accretion and the energy of the black hole itself. The general theory of relativity predicts a remarkable statement that a spinning black hole has free energy available to be tapped.

Research at Columbia University reveals that spinning black holes have rotational energy that can be extracted. Study shows that when a black hole is immersed in externally supplied magnetic field, reconnection of magnetic field lines within ergo sphere can generate negative energy particles that fall into black hole event of horizon while other particle escapes stealing energy from black hole. Research has proved analytically that energy extraction via magnetic reconnection is possible when black hole spin is high and plasma is strongly magnetized. This energy extraction depends on plasma magnetization and orientation of reconnecting magnetic field lines.

It was shown by Christoduolou that a black hole has a portion with irreducible mass which has one to one correspondence with surface area of the event of horizon that is proportional to black hole entropy. During the calculations it was found that this violate the second law of thermodynamics but later confirmed it does not and this results in theory that a substantial amount of black hole energy can be extracted.

How It Is Possible?

The possibility of extracting black hole rotational energy was realized by Penrose who envisioned an experiment in which particle fission occurs in ergo sphere surrounding a rotating black hole. This Penrose process indicates that it is possible to extract energy from black hole which is believed to be impractical in astrophysical phenomena. There are alternate mechanisms proposed to extract black hole rotational energy such as Super Radiant Scattering, the Collisional Penrose process, the Blanford-Znack process and the Magneto Hydrodynamic Penrose process. The Penrose process suggests that two new born particles when separate relative with velocity greater than half the speed of light while in Blanford-Znack process energy is extracted electromagnetically through magnetic field supported by accretion disk around the black hole – is thought to be leading mechanism for powering the relativistic jets of Active Galactic Nuclei (AGN) and Gamma Ray Burst (GRBs). Worldwide scientists are looking for different mechanism to extract energy from black hole but the possibility of extracting black hole rotational energy as a result of rapid reconnection of magnetic field lines has been generally overlooked.




The possibility of extracting black hole rotational energy via negative-energy particles requires magnetic reconnection to take place in the ergosphere of the spinning black hole since the static limit is the boundary of the region containing negative-energy orbits. Magnetic reconnection inside the ergosphere is expected to occur routinely for fast rotating black holes. Indeed, a configuration with antiparallel magnetic field lines that is prone to magnetic reconnection is caused naturally by the frame-dragging effect of a rapidly spinning black hole. Scientists had envisioned the situation where the fast rotation of the black hole leads to antiparallel magnetic field lines adjacent to the equatorial plane. This scenario is also consistent with numerical simulations of rapidly spinning black holes. The change in magnetic field direction at the equatorial plane produces an equatorial current sheet. This current sheet forms dynamically and is destroyed by the plasmoid instability (permitted by non-ideal magneto hydrodynamic effects such as thermal-inertial effects, pressure agyrotropy, or electric resistivity) when the current sheet exceeds a critical aspect ratio. The formation of plasmoids ropes drives fast magnetic reconnection which rapidly converts the available magnetic energy into plasma particle energy. Eventually, the plasma is expelled out of the reconnection layer and the magnetic tension that drives the plasma outow relaxes. The field lines are then stretched again by the frame-dragging effect and a current layer prone to fast plasmoid-mediated reconnection forms again. This leads to reconnecting current sheets that form rapidly and intermittently. Magnetic reconnection in the plasma that rotates around the black hole has the effect of accelerating part of the plasma and decelerating another part. If the decelerated plasma has negative energy at infinity and the accelerated one has energy at infinity larger than its rest mass and thermal energies then the plasma that escapes to infinity acquires energy at the expense of the black hole rotational energy when the negative-energy particles are swallowed by the black hole as in the standard Penrose process.

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