Kesden, Michael and Lockhart, Guglielmo and Phinney, E. Sterl (2010) Maximum blackhole spin from quasicircular binary mergers. Physical Review D, 82 (12). Art. No. 124045. ISSN 05562821. http://resolver.caltech.edu/CaltechAUTHORS:20110302090724602

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Abstract
Black holes of mass M must have a spin angular momentum S below the Kerr limit (χ ≡ S/M^2 ≤ 1), but whether astrophysical black holes can attain this limiting spin depends on their accretion history. Gas accretion from a thin disk limits the blackhole spin to χ_(gas) ≲ 0.9980 ± 0.0002, as electromagnetic radiation from this disk with retrograde angular momentum is preferentially absorbed by the black hole. Extrapolation of numericalrelativity simulations of equalmass binary blackhole mergers to maximum initial spins suggests these mergers yield a maximum spin χ_(eq) ≲ 0.95. Here we show that for smaller mass ratios q ≡ m/M ≪ 1, the superradiant extraction of angular momentum from the larger black hole imposes a fundamental limit χ_(lim) ≲ 0.9979 ± 0.0001 on the final blackhole spin even in the testparticle limit (q→0) of binary blackhole mergers. The nearly equal values of χ_(gas) and χ_(lim) imply that measurement of supermassive blackhole spins cannot distinguish a black hole built by gas accretion from one assembled by the gravitational inspiral of a disk of compact stellar remnants. We also show how superradiant scattering alters the mass and spin predicted by models derived from extrapolating testparticle mergers to finite mass ratios.
Item Type:  Article  

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Additional Information:  © 2010 American Physical Society. Received 29 October 2010; published 20 December 2010. We thank Scott Hughes for generously allowing us to use a version of his GREMLIN (Gravitational Radiation in the Extreme Mass ratio LIMit) code to calculate the energy and angular momentum radiated during the inspiral. We also thank Andrew Benson, Chris Hirata, Pedro Marronetti, Uli Sperhake, and Kip Thorne for useful conversations. The authors acknowledge support from NASA BEFS Grant No. NNX07AH06G (PI:Phinney). M. Kesden also acknowledges support from NSF Grant No. PHY 0601459 (PI: Thorne).  
Group:  TAPIR  
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Classification Code:  PACS: 04.70.Bw, 04.25.Nx, 04.30.Db, 04.30.Tv  
Record Number:  CaltechAUTHORS:20110302090724602  
Persistent URL:  http://resolver.caltech.edu/CaltechAUTHORS:20110302090724602  
Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided.  
ID Code:  22592  
Collection:  CaltechAUTHORS  
Deposited By:  Benjamin Perez  
Deposited On:  03 Mar 2011 04:44  
Last Modified:  26 Dec 2012 12:59 
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