Estimating the fossil disc mass during supermassive black hole mergers: the importance of torque implementation
Articolo
Data di Pubblicazione:
2015
Citazione:
Estimating the fossil disc mass during supermassive black hole mergers: the importance of torque implementation / M. Tazzari, G. Lodato. - In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - ISSN 0035-8711. - 449:1(2015 May 01), pp. 1118-1128.
Abstract:
In this paper, we revisit the issue of estimating the ‘fossil’ disc mass in the circumprimary disc,
during the merger of a supermassive black hole binary. As the binary orbital decay speeds up
due to the emission of gravitational waves, the gas in the circumprimary disc might be forced
to accrete rapidly and could in principle provide a significant electromagnetic counterpart
to the gravitational wave emission. Since the luminosity of such flare is proportional to the
gaseous mass in the circumprimary disc, estimating such mass accurately is important. Previous
investigations of this issue have produced contradictory results, with some authors estimating
super-Eddington flares and large disc mass, while others suggesting that the ‘fossil’ disc mass
is very low, even less than a Jupiter mass. Here, we perform simple 1D calculations to show
that such very low estimates of the disc mass are an artefact of the specific implementation
of the tidal torque in 1D models. In particular, for moderate mass ratios of the binary, the
usual formula for the torque used in 1D models significantly overestimates the width of the
gap induced by the secondary and this artificially leads to a very small leftover circumprimary
disc. Using a modified torque, calibrated to reproduce the correct gap width as estimated by
3D models, leads to fossil disc masses of the order of one solar mass. The rapid accretion of
the whole circumprimary disc would produce peak luminosities of the order of 1–20 times the
Eddington luminosity. Even if a significant fraction of the gas escapes accretion by flowing out
the secondary orbit during the merger (an effect not included in our calculations), we would
still predict close to Eddington luminosities that might be easily detected.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
Accretion, accretion discs; Black hole physics; Galaxies: formation; Gravitational waves; Hydrodynamics
Elenco autori:
M. Tazzari, G. Lodato
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