TY - JOUR

T1 - Theory and astrophysical consequences of a magnetized torus around a rapidly rotating black hole

AU - Van Putten, Maurice H.P.M.

AU - Levinson, Amir

PY - 2003/2/20

Y1 - 2003/2/20

N2 - We analyze the topology, lifetime, and emissions of a torus around a black hole formed in hypernovae and black hole-neutron star coalescence. The torus is ab initio uniformly magnetized, represented by two counteroriented current rings, and develops a state of suspended accretion against a "magnetic wall" around the black hole. Magnetic stability of the torus gives rise to a new fundamental limit ℰℬ/k < 0.1 for the ratio of poloidal magnetic field energy to kinetic energy, corresponding to a maximum magnetic field strength Bc ≃ (1016 G)(7 M⊙/MH)(6MH/R)2(M T/0.03MH)1/2. The lifetime of rapid spin of the black hole, effectively defined by the timescale of dissipation of spin energy Erot in the horizon, hereby satisfies T ≃ (40 s) (M H/7 M⊙)(R/6MH)4(0.03MH/M T) for a black hole of mass MH surrounded by a torus of mass MT and radius R. The torus converts a major fraction E gw/Erot ∼ 10% into gravitational radiation through a finite number of multipole mass moments and a smaller fraction into MeV neutrinos and baryon-rich winds. At a source distance of 100 Mpc, these emissions over N = 2 × 104 periods give rise to a characteristic strain amplitude N1/2hchar ≃ 6 × 10-21. We argue that torus winds create an open magnetic flux tube on the black hole, which carries a minor fraction Ej/E rot ≃ 10-3 in baryon-poor outflows to infinity. We conjecture that these are not high-σ outflows, owing, in part, to magnetic reconnection in surrounding current sheets. The fraction E j/Erot ∼ 1/4 (MH/R)4 is standard for a universal horizon half-opening angle θH ≃ MH/R of the open flux tube. We identify this baryon-poor output of tens of seconds with gamma-ray bursts with contemporaneous and strongly correlated emissions in gravitational radiation, conceivably at multiple frequencies. Ultimately, this leaves a black hole binary surrounded by a supernova remnant.

AB - We analyze the topology, lifetime, and emissions of a torus around a black hole formed in hypernovae and black hole-neutron star coalescence. The torus is ab initio uniformly magnetized, represented by two counteroriented current rings, and develops a state of suspended accretion against a "magnetic wall" around the black hole. Magnetic stability of the torus gives rise to a new fundamental limit ℰℬ/k < 0.1 for the ratio of poloidal magnetic field energy to kinetic energy, corresponding to a maximum magnetic field strength Bc ≃ (1016 G)(7 M⊙/MH)(6MH/R)2(M T/0.03MH)1/2. The lifetime of rapid spin of the black hole, effectively defined by the timescale of dissipation of spin energy Erot in the horizon, hereby satisfies T ≃ (40 s) (M H/7 M⊙)(R/6MH)4(0.03MH/M T) for a black hole of mass MH surrounded by a torus of mass MT and radius R. The torus converts a major fraction E gw/Erot ∼ 10% into gravitational radiation through a finite number of multipole mass moments and a smaller fraction into MeV neutrinos and baryon-rich winds. At a source distance of 100 Mpc, these emissions over N = 2 × 104 periods give rise to a characteristic strain amplitude N1/2hchar ≃ 6 × 10-21. We argue that torus winds create an open magnetic flux tube on the black hole, which carries a minor fraction Ej/E rot ≃ 10-3 in baryon-poor outflows to infinity. We conjecture that these are not high-σ outflows, owing, in part, to magnetic reconnection in surrounding current sheets. The fraction E j/Erot ∼ 1/4 (MH/R)4 is standard for a universal horizon half-opening angle θH ≃ MH/R of the open flux tube. We identify this baryon-poor output of tens of seconds with gamma-ray bursts with contemporaneous and strongly correlated emissions in gravitational radiation, conceivably at multiple frequencies. Ultimately, this leaves a black hole binary surrounded by a supernova remnant.

KW - Black hole physics

KW - Gamma rays: bursts

KW - Gravitational waves

UR - http://www.scopus.com/inward/record.url?scp=0042740448&partnerID=8YFLogxK

U2 - 10.1086/345900

DO - 10.1086/345900

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AN - SCOPUS:0042740448

SN - 0004-637X

VL - 584

SP - 937

EP - 953

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 2 I

ER -