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Retrograde accretion and merging supermassive black holes

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journal contribution
posted on 24.10.2012, 09:06 by P. J. Cossins, A. R. King, J. E. Pringle
We investigate whether a circumbinary gas disc can coalesce a supermassive black hole binary system in the centre of a galaxy. This is known to be problematic for a prograde disc. We show that in contrast, interaction with a retrograde circumbinary disc is considerably more effective in shrinking the binary because there are no orbital resonances. The binary directly absorbs negative angular momentum from the circumbinary disc by capturing gas into a disc around the secondary black hole, or discs around both holes if the binary mass ratio is close to unity. In many cases the binary orbit becomes eccentric, shortening the pericentre distance as the eccentricity grows. In all cases the binary coalesces once it has absorbed the angular momentum of a gas mass comparable to that of the secondary black hole. Importantly, this conclusion is unaffected even if the gas inflow rate through the disc is formally super-Eddington for either hole. The coalescence time-scale is therefore always Graphic, where M2 is the secondary black hole mass and Graphic the inflow rate through the circumbinary disc.

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Citation

Monthly Notices of the Royal Astronomical Society , 2011, 412 (3), pp. 1591-1598

Version

VoR (Version of Record)

Published in

Monthly Notices of the Royal Astronomical Society

Publisher

Oxford University Press (OUP)

issn

0035-8711

eissn

1365-2966

Copyright date

2011

Available date

24/10/2012

Publisher version

http://mnras.oxfordjournals.org/content/412/3/1591

Language

en

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