Energy extraction from boosted black holes: Penrose process, jets, and the membrane at infinity

Abstract

Numerical simulations indicate that black holes carrying linear momentum and/or orbital momentum can power jets. The jets extract the kinetic energy stored in the black hole's motion. This could provide an important electromagnetic counterpart to gravitational wave searches. We develop the theory underlying these jets. In particular, we derive the analogues of the Penrose process and the Blandford-Znajek jet power prediction for boosted black holes. The jet power we find is ðv=2MÞ 2 Φ 2 =ð4πÞ, where v is the hole's velocity, M is its mass, and Φ is the magnetic flux. We show that energy extraction from boosted black holes is conceptually similar to energy extraction from spinning black holes. However, we highlight two key technical differences: in the boosted case, jet power is no longer defined with respect to a Killing vector, and the relevant notion of black hole mass is observer dependent. We derive a new version of the membrane paradigm in which the membrane lives at infinity rather than the horizon and we show that this is useful for interpreting jets from boosted black holes. Our jet power prediction and the assumptions behind it can be tested with future numerical simulations.

Prompt electromagnetic transients from binary black hole mergers

“…Several numerical [49,50,52,93] and analytical [94][95][96][97] studies have investigated how even non-spinning black holes in an orbital configuration can generate Poynting luminosities in the limit of force-free MHD through a process similar to the Blandford-Znajek mechanism [88] for jets powered by a black hole. In Blandford-Znajek, the twisting of magnetic field lines in interaction with a spinning black hole converts kinetic energy to jet power.…”

Bright transients from strongly-magnetized neutron star-black hole mergers

“…The BHNS system behaves analogously to a unipolar inductor, which has been investigated in application to a number of other astrophysical systems, e.g. Jupiter and its moon Io [9], planets around white dwarfs [10] and main sequence stars [11,12], binary neutron stars [13][14][15][16], compact white dwarf binaries [15,[17][18][19], BHs boosted through magnetic fields [20,21], and the Blandford-Znajek (BZ) mechanism [22] for a single BH spinning in a magnetic field (for recent numerical work on the BZ mechanism see, e.g., [23,24]). The calculation for BHNS systems, already presented in Ref.…”

Near-horizon BMS symmetries as fluid symmetries

“…On the other hand, a version of the membrane paradigm can be defined at null infinity [15]. The problem simplifies in three spacetime dimensions.…”

“…membrane paradigm [10][11][12][13][14][15] and the fluid/gravity correspondence [16]. We derived BMS conservation laws from membrane paradigm dynamics in [17] and the relationship between BMS and fluids was also pursued by [18,19] from a somewhat different perspective.…”