Spinning up black holes with super-critical accretion flows

A. Sądowski¹, M. Bursa², M. Abramowicz^1,2,3,4, W. Kluźniak¹, J.-P. Lasota^5,6, R. Moderski¹ and M. Safarzadeh^3,7

¹ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warszawa, Poland
e-mail: as@camk.edu.pl; wlodek@camk.edu.pl; moderski@camk.edu.pl
² Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401/1a, 141-31 Praha 4, Czech Republic
e-mail: bursa@astro.cas.cz
³ Department of Physics, Göteborg University, 412-96 Göteborg, Sweden
e-mail: marek.abramowicz@physics.gu.se
⁴ Department of Physics, Silesian University at Opava, Bezručovo náměstí 1150/13, 74601 Opava, Czech Republic
⁵ Institut d’Astrophysique de Paris, UMR 7095 CNRS, UPMC Univ. Paris 06, 98bis Bd Arago, 75014 Paris, France
e-mail: lasota@iap.fr
⁶ Jagiellonian University Observatory, ul. Orla 171, 30-244 Kraków, Poland
⁷ Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street Baltimore, MD 21218, USA
e-mail: mts@pha.jhu.edu

Received: 11 February 2011
Accepted: 24 May 2011

Abstract

We study the process of spinning up black holes by accretion from slim disks for a wide range of accretion rates. We show that for super-Eddington accretion rates and low values of the viscosity parameter α ( ≲ 0.01) the limiting value of the dimensionless spin parameter a_∗ can reach values higher than a_∗ = 0.9978 inferred by Thorne in his seminal study. For Ṁ = 10   Ṁ_Edd and α = 0.01, spin equilibrium is reached at a_∗ = 0.9994. We show that the equilibrium spin value depends strongly on the assumed value of α. We also prove that for high accretion rates the impact of captured radiation on spin evolution is negligible.