Fewbody Interactions
in Galactic Nuclei
Nathan W. C. Leigh
Kalbfleisch Fellow
American Museum of Natural History
Department of Physical Sciences
The Exciting Lives of Galactic Nuclei
Tegernsee, Germany
Feb. 26 - Mar. 3, 2017
Leigh et al.2017,
in preparation
The triple star
candidates reported
here constitute the
tip of the iceberg;
triples are common
in Galactic GCs.
Leigh et al.2017,
in preparation
The triple star
candidates reported
here constitute the
tip of the iceberg;
triples are common
in Galactic GCs.
Leigh et al.2017,
in preparation
The triple star
candidates reported
here constitute the
tip of the iceberg;
triples are common
in Galactic GCs.
Galactic Nuclei
Leigh et al.2017,
in preparation
Collisional Dynamics in Galactic Nuclei:
Missing Physics
Can use observations of multiple star systems to constrain the
underlying dynamical environment!
•
Efficient binary destruction via energetic encounters with single stars in
collisionally evolved systems
•
•
•
•
Binary preservation or formation?
•
•
•
•
•
Very low multiplicity (binary, triple, etc.) fractions?
“Exotic” mechanisms for binary formation?
The role of remnants?
Exchange interactions with remnants that “destroy” photometric binaries, but preserve
the “true” binary fraction?
Primordial? Recent star formation?
Tidal captures? GW captures?
3-body encounters?
Efficient binary hardening?
•
•
•
Dynamical interactions with single stars?
Gravitational wave emission?
Kozai cycles with the central SMBH?
Collisional Dynamics in Galactic Nuclei:
Missing Physics
Can use observations of multiple star systems to constrain the
underlying dynamical environment!
•
Efficient binary destruction via energetic encounters with single stars in
collisionally evolved systems
•
•
•
•
Binary preservation or formation?
•
•
•
•
•
Very low multiplicity (binary, triple, etc.) fractions?
“Exotic” mechanisms for binary formation?
The role of remnants?
Exchange interactions with remnants that “destroy” photometric binaries, but preserve
the “true” binary fraction?
Primordial? Recent star formation?
Tidal captures? GW captures?
3-body encounters?
Efficient binary hardening?
•
•
•
Dynamical interactions with single stars?
Gravitational wave emission?
Kozai cycles with the central SMBH?
~1 binary
destroyed
per Myr
~20 binaries
destroyed
per Myr
Direct stellar
collisions!
Number of
collisions per
Myr in each 0.1
pc radial bin.
~10 binaries
destroyed
per Myr
~10 binaries
destroyed
per Myr
MS-MS
WD-MS
1+2
BH-MS
Leigh et al. 2016,
MNRAS, 463, 1605
Binary Hardening and
Destruction
Consider a stellar-mass BH-BH binary
located at the influence radius of an SMBH
in a Milky Way-like nuclear star cluster…
rinf
SMBH
(M = 106 MSun)
BH-BH binary
Isotropic
Planar
>90% of BH-BH
binaries are
disrupted before
merging!
104 BH-BH
binaries with the
indicated initial
binary separation
and component
masses of 10
MSun and 15
MSun.
Each binary is
evolved by both
dynamical
hardening and
inter-encounter
GW emission.
Leigh, Geller et al.
2017, in preparation
“Exotic” Channels for Binary Formation?
Multiples are sensitive probes of the underlying dynamical
environment and its constituents; their preservation,
formation and eventual fate all depend on it.
•
Even BH-BH binaries struggle to survive in galactic nuclei
•
•
•
The rate of 1+2 interactions exceeds the rate of 2+2 interactions for binary
fractions fb < 10%
•
•
•
Low binary fractions in NSCs; even including remnants
GW sources require at least one massive BH?
2+2 interactions should not occur
Triples should not be present
“Exotic” channels for binary formation in a Keplerian potential?
•
•
Migration traps of AGN disks?
3-body encounters with the separations of all 3 orbits slightly exceeding their Hill
radii?
Consider a stellar-mass BH-BH binary
located at a migration trap in an AGN
disk…
Stars with their AGN disk
orbits ground down
in to the disk
Migration trap
~200Rg
SMBH
(M = 108 MSun)
BH-BH binary
Isotropic
Planar
100% of BH-BH
binaries merge!
104 BH-BH
binaries with the
indicated initial
binary separation
and component
masses of 10
MSun and 15
MSun.
Each binary is
evolved by both
dynamical
hardening and
inter-encounter
GW emission.
McKernan et al.
2017, submitted
Leigh, Geller et al.
2017, in preparation
Summary
•
•
Multiple star systems should be rare in galactic nuclei, but
nevertheless important
•
Multiples are sensitive probes of the underlying dynamical
environment
•
Binary preservation, formation and their eventual fate depend on it
BH-BH binaries are easily (>90%) disrupted via 1+2
encounters in most NSC environments
•
Need at least one massive BH for mergers?
Planar scatterings favor mergers over isotropic scatterings
•
Higher BH-BH merger rates in NSCs with higher v/sigma?
•
•
“Exotic” channels for binary formation in a Keplerian
potential?
•
•
The migration traps of AGN disks?
3-body interactions?