Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ultramassive Black Hole Coalescence   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 NGC1277 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 NGC1277 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 3-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 an rapid
and efficient SMBH coalescence timescale. We discuss the implications for
gravitational wave event rates and hypervelocity star production.

31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
20
The categories of this paper are: acc-phys
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
1
The categories of this paper are: cs
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio