Ultra-high-energy debris from the collisional Penrose process

Abstract

Soon after the discovery of the Kerr metric, Penrose realized that superradiance can be exploited to extract energy from black holes. The original idea (involving the breakup of a single particle) yields only modest energy gains. A variant of the Penrose process consists of particle collisions in the ergoregion. The collisional Penrose process has been explored recently in the context of dark matter searches, with the conclusion that the ratio $\eta$ between the energy of post-collision particles detected at infinity and the energy of the colliding particles should be modest ($\eta \lesssim 1.5$). Schnittman has shown that these studies underestimated the maximum efficiency by about one order of magnitude (i.e., $\eta \lesssim 15$). In this work we show that particle collisions in the vicinity of rapidly rotating black holes can produce high-energy ejecta and result in high efficiencies under much more generic conditions. The astrophysical likelihood of these events deserves further scrutiny, but our study hints at the tantalizing possibility that the collisional Penrose process may power gamma rays and ultra-high-energy cosmic rays.

5 pages, 7 figures. v2: Unabridged version of the Letter in press in PRL. This arXiv version contains supplemental material in response to http://arxiv.org/abs/1501.01984

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• Circular geodesics in Kerr-Newman-Kasuya black hole
• Consistent analytic approach to the efficiency of collisional Penrose process
• Self-consistent multidimensional Penrose process driven by magnetic reconnection
• Electromagnetic radiation reaction and energy extraction from black holes: The tail term cannot be ignored
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• Amplification of gravitational wave by a Kerr black hole
• Observability of Zero-angular-momentum Sources Near Kerr Black Holes
• The effect of the WGC condition on the maximal energy extracted from black holes
• Is there a trade-off relation between efficiency and power in a collisional Penrose process in an extreme Reissner-Nordström spacetime?
• Collisional Penrose process of extended test particles near an extremal Kerr black hole