Journal Article

Retrograde accretion and merging supermassive black holes

C. J. Nixon, P. J. Cossins, A. R. King and J. E. Pringle

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 412, issue 3, pages 1591-1598
Published in print April 2011 | ISSN: 0035-8711
Published online April 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17952.x
Retrograde accretion and merging supermassive black holes

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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 , where M2 is the secondary black hole mass and the inflow rate through the circumbinary disc.

Keywords: accretion, accretion discs; black hole physics; galaxies: active; galaxies: formation; cosmology: theory

Journal Article.  6062 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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