Supermassive black holes, accretion discs, stellar dynamics and tidal disruptions
Final Report Abstract
In this DFG-funded project we have addressed the formation of black hole binary systems, for two particular regimes: dense stellar systems, where we expect binaries to form among stellar-mass black holes, and the nuclei of galaxies, where supermassive black holes are very likely lurking. The first part of this project was devoted to the presentation of a new directsummation N−body code which we have written totally from scratch, along with a suit of very-well known tests in the community of stellar dynamics, which the code successfully passed. The code is a Swiss army knife that can be used to investigate many different problems, although the prime goal was the formation of binaries of black holes. This is the reason why we included a relativistic treatment for the evolution of orbits of black holes when they reach relativistic speeds. Our immediate future goal is to start doing realistic simulations of clusters to follow the formation and evolution of such binaries, as a way to understand what the orbital parameters of black holes are when they are on their way to coalesce. The code is public and it has been downloaded by many people which have contacted us to get involved in their research. The second part deals with massive black holes and accretion discs. In particular, we were interested in understanding the interplay between such massive binaries and the gas which might be surrounding it. The first important aspect we investigated was the assumption made by many different groups as regards the amount of gas accreted by counter-rotating binaries of massive black holes, and we have shown that the way gas is usually assumed to be accreted leads to wrong results. In our study we derive a prescription that should be adopted for a correct evolution of the system. As we were interested in understanding the very fundamental questions in which we base our progress for the problem of binaries, in the third part of this project we questioned the formation of disc-like structures around these binaries of massive black holes, and the evolution of the binary itself in a more realistic scenario, such as galactic centres. What we found is that the formation of disc-like structures around the binary seems to be a particular, episodic event in a much more complex situation. Various structures form, and they have different impacts on to the evolution of the binary itself. We envisage the research we have done in this project as not complete. It is an important first, solid step towards the understanding of how binaries of stellar-mass- or supermassive black holes form. We live a very vibrant time in this field, which will lead to the answers of many questions and, undoubtedly, to many more new questions.
Publications
- “Infalling clouds on to supermassive black hole binaries - I. Formation of discs, accretion and gas dynamics”, Monthly Notices of the Royal Astronomical Society, Volume 455, Issue 2, p.1989-2003 (2016)
Goicovic, F. G.; Cuadra, J.; Sesana, A.; Stasyszyn, F.; Amaro-Seoane, P.; Tanaka, T. L.
(See online at https://doi.org/10.1093/mnras/stv2470) - “Retrograde binaries of massive black holes in circumbinary accretion discs”, Astronomy & Astrophysics, Volume 591, id.A114, 12 pp. (2016)
Amaro-Seoane, Pau; Maureira-Fredes, Cristián; Dotti, Massimo; Colpi, Monica
(See online at https://doi.org/10.1051/0004-6361/201526172) - “Accretion of clumpy cold gas onto massive black hole binaries: a possible fast route to binary coalescence”, Monthly Notices of the Royal Astronomical Society, Volume 479, Issue 3, p. 3438-3455 (2018)
Goicovic, Felipe G.; Maureira-Fredes, Cristian; Sesana, Alberto; Amaro-Seoane, Pau; Cuadra, Jorge
(See online at https://doi.org/10.1093/mnras/sty1709) - “Accretion of clumpy cold gas onto massive black holes binaries: the challenging formation of extended circumbinary structures”, Monthly Notices of the Royal Astronomical Society, Volume 478, Issue 2, p.1726-1748 (2018)
Maureira-Fredes, Cristián; Goicovic, Felipe G.; Amaro-Seoane, Pau; Sesana, Alberto
(See online at https://doi.org/10.1093/mnras/sty1105) - “GraviDy, a GPU modular, parallel direct-summation N-body integrator: Dynamics with softening”, Monthly Notices of the Royal Astronomical Society, Volume 473, Issue 3, p.3113-3127 (2018)
Maureira-Fredes, Cristián; Amaro-Seoane, Pau
(See online at https://doi.org/10.1093/mnras/stx2468)
