## Abstract

We study the dynamics of supermassive black hole binaries embedded in circumbinary gaseous discs, with the smoothed particle hydrodynamics code gadget-2. The subparsec binary (of total mass M and mass ratio q= 1/3) has excavated a gap and transfers its angular momentum to the self-gravitating disc (M_{disc}= 0.2M). We explore the changes of the binary eccentricity, e, by simulating a sequence of binary models that differ in the initial eccentricity e_{0} only. In initially low-eccentric binaries, the eccentricity increases with time, while in high-eccentric binaries e declines, indicating the existence of a limiting eccentricity e_{crit} that is found to fall in the interval [0.6, 0.8]. We also present an analytical interpretation for this saturation limit. An important consequence of the existence of e_{crit} is the detectability of a significant residual eccentricity e_{LISA} by the proposed gravitational wave detector Laser Interferometer Space Antenna (LISA). It is found that at the moment of entering the LISA frequency domain e_{LISA}~ 10^{-3}-10^{-2}, a signature of its earlier coupling with the massive circumbinary disc. We also observe large periodic inflows across the gap, occurring on the binary and disc dynamical time-scales rather than on the viscous time. These periodic changes in the accretion rate (with amplitudes up to ~100 per cent, depending on the binary eccentricity) can be considered a fingerprint of eccentric subparsec binaries migrating inside a circumbinary disc.

Original language | English |
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Pages (from-to) | 3033-3041 |

Number of pages | 9 |

Journal | Monthly Notices of the Royal Astronomical Society |

Volume | 415 |

Issue number | 4 |

DOIs | |

State | Published - Aug 2011 |

Externally published | Yes |

## Keywords

- Accretion, accretion discs
- Black hole physics
- Gravitational waves
- Methods: numerical