#### Alladi Ramakrishnan Hall

#### Rotating black holes as power sources

#### Pankaj Sheoran

##### Jamia Milia Islamia, New Delhi

*In 1971 Roger Penrose pointed out that it was possible to extract the*

the rotational energy of the Kerr black hole (BH), when a massive

particle enters into the ergosphere and splits up there into two. The

momentum of the two particles can be arranged in such a manner that

one piece escapes to infinity with energy greater than that of

incoming particle, while the other falls inside the event horizon of

the black hole. But through this process, we can extract at maximum

only 20% of energy of BH. Here, we investigate the properties of the

horizons and ergosphere in a rotating higher dimensional (HD) deformed

Kerr-like BH. Furthermore, we explicitly bring out the effect of

deformation parameter (ε) and the extra dimension (D) on the

efficiency of the Penrose process. It is interesting to see that the

ergosphere size is sensitive to the (ε) as well as spacetime

dimensions D. This gives rise to a much richer structure of the

ergosphere in a HD deformed Kerr BH, thereby making the Penrose

process more efficient compared with that of the four-dimensional Kerr

black hole.

We have also studied the Banados, Silk and West (BSW) effect for

rotating regular Ayón-Beato- García (ABG) BH in which two massive

particles moving in the equatorial plane collide near the event

horizon of a BH and the energy of their center-of-mass (CM) can grow

unbounded under certain conditions. It turns out that CM energy

depends not only on rotation parameter (a) as suggested by BSW but

also on charge (Q). Particularly for the extremal rotating regular ABG

BH, the CM energy of two colliding particles could be arbitrarily high

for the critical angular momentum of particles. Also, we have shown

that, for a nonextremal BH, there exists a finite upper limit of CM

energy, which changes with Q. Finally, we made a comparison with Kerr

and Kerr- Newman BHs.

Done