ULTRAMASSIVE BLACK HOLE COALESCENCE

Journal Article · Sat Jan 10 04:00:00 EST 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/798/2/103· OSTI ID:22364641

Khan, Fazeel Mahmood ^[1]; Holley-Bockelmann, Kelly ^[2]; Berczik, Peter ^[3]

---

1. Department of Space Science, Institute of Space Technology, PO Box 2750, Islamabad (Pakistan)
2. Department of Physics and Astronomy, Vanderbilt University, Nashville, TN (United States)
3. National Astronomical Observatories of China, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, 100012 Beijing (China)

Although supermassive black holes (SMBHs) correlate well with their host galaxies, there is an emerging view that outliers exist. Henize 2-10, NGC 4889, and NGC 1277 are examples of SMBHs at least an order of magnitude more massive than their host galaxy suggests. The dynamical effects of such ultramassive central black holes is unclear. Here, we perform direct N-body simulations of mergers of galactic nuclei where one black hole is ultramassive to study the evolution of the remnant and the black hole dynamics in this extreme regime. We find that the merger remnant is axisymmetric near the center, while near the large SMBH influence radius, the galaxy is triaxial. The SMBH separation shrinks rapidly due to dynamical friction, and quickly forms a binary black hole; if we scale our model to the most massive estimate for the NGC 1277 black hole, for example, the timescale for the SMBH separation to shrink from nearly a kiloparsec to less than a parsec is roughly 10 Myr. By the time the SMBHs form a hard binary, gravitational wave emission dominates, and the black holes coalesce in a mere few Myr. Curiously, these extremely massive binaries appear to nearly bypass the three-body scattering evolutionary phase. Our study suggests that in this extreme case, SMBH coalescence is governed by dynamical friction followed nearly directly by gravitational wave emission, resulting in a rapid and efficient SMBH coalescence timescale. We discuss the implications for gravitational wave event rates and hypervelocity star production.

• OSTI ID: 22364641
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 798; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
AXIAL SYMMETRY
BLACK HOLES
COALESCENCE
COMPUTERIZED SIMULATION
GALAXIES
GALAXY NUCLEI
GRAVITATIONAL WAVES
SCATTERING
STAR CLUSTERS
STAR EVOLUTION
STAR MODELS
STARS
THREE-BODY PROBLEM