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Close encounters between Close encounters between stars and Massive Black Holesstars and Massive Black Holes
Clovis HopmanClovis HopmanWeizmann Institute of ScienceWeizmann Institute of Science
IsraelIsrael
AdvisorAdvisor: : Tal Tal AlexanderAlexander
Tidally powered stars in the Galactic Tidally powered stars in the Galactic CenterCenter
Ultraluminous X-ray sourcesUltraluminous X-ray sources Gravitational Wave RadiationGravitational Wave Radiation
Dissipative stellar processes Dissipative stellar processes near Massive Black Holesnear Massive Black Holes
Tides and Gravity Waves
2BH2
c
GM=rSStar
3/1
Star
BH RM
M=rt
6
2TIDAL
p
t
r
rTE
2/7
p
SGWR r
r
E
Tides GWR
Kozai mechanism near Kozai mechanism near MBHsMBHs
Deviations from spherical symmetry in GC?
Kozai eccentricity oscillations drive stars effectively towards the MBH (Hopman, Subr & Alexander 2005, in prep.)
1>>star ofenergy Binding
at energy Orbital2/3
Star
BH
M
M~
rt
Squeezars in Galactic Centers are transient sources
Surviving tidal heatingSurviving tidal heating
Survival: low mass MBHs and efficient cooling
SqueezarsSqueezars
Stars powered by tidal “squeezing” Stars powered by tidal “squeezing” Squeezars observable in Galactic Squeezars observable in Galactic
Center Center (Alexander & Morris, ApJL 2003)(Alexander & Morris, ApJL 2003)
~ 1 squeezar in GC ~ 1 squeezar in GC (Alexander & Hopman, ApJL (Alexander & Hopman, ApJL 2003)2003)
Kozai: many more squeezars? Kozai: many more squeezars? (Hopman, (Hopman, Subr & Alexander 2005, in prep.)Subr & Alexander 2005, in prep.)
Squeezars evaporate near MBHsSqueezars evaporate near MBHs
Ultraluminous X-ray SourcesUltraluminous X-ray Sources
Super Eddington luminosities Super Eddington luminosities IBH: engine of ULX?IBH: engine of ULX? IBH can be formed dynamically IBH can be formed dynamically
in cluster in cluster (Portegies Zwart et al., Nature 2004)(Portegies Zwart et al., Nature 2004)
What feeds the IBH??What feeds the IBH??
Clusters contain too little gasClusters contain too little gas Tidal disruption of star gives only Tidal disruption of star gives only
short (~yr) flare short (~yr) flare (Rees, Nature 1988)(Rees, Nature 1988)
Solution: Tidal Capture!
ULX: ULX: IBH fed by a tidally captured IBH fed by a tidally captured
starstar
Circularization possible around IBHCircularization possible around IBH Roche lobe overflow supplies gasRoche lobe overflow supplies gas ULX can switch on after cluster ULX can switch on after cluster
evaporatesevaporates Lifetime and luminosity as observedLifetime and luminosity as observed
CircularizationCircularization
r
max
p
in
p
t
)aN(<~Γ
at<t
a>a
r
:rate cone-lossEmpty
:Scattering vsInspiral
:truncation-Cusp
periapse minimal :Eddington
max0
min,
Hopman, Portegies Zwart & Alexander, ApJL 2004
N-body simulations show tidal capture (Baumgardt, Hopman & Portegies Zwart 2005, in prep.)
Captured StarsCaptured Stars
sun5
max 10 mass BH Maximal M~M
Rate independent of relaxation time
Hopman, Portegies Zwart & Alexander, ApJL 2004
Probability = Capture Rate Stellar Lifetime 10 %
Hopman, Portegies Zwart & Alexander, ApJL 2004
Mass Transfer and Mass Transfer and LuminosityLuminosity
Monte Carlo tracks in phase Monte Carlo tracks in phase spacespace
Hopman & Alexander, astro-ph/0503672 .
Length scale ac delimits volume of inspiral stars
Stars perform random walk in phase space
LISA Stars in the Strong LISA Stars in the Strong Gravity RegimeGravity Regime
Hopman & Alexander, astro-ph/0503672 .
Massive Black Holes: Intermediate Mass Black Holes:
Mass segregation: Heavy stars closer Mass segregation: Heavy stars closer to MBH!to MBH!
Rate independent of relaxation timeRate independent of relaxation time Orbits are very eccentricOrbits are very eccentric Probably no signal from IBHsProbably no signal from IBHs
Hopman & Alexander, astro-ph/0503672 .
ConclusionsConclusions
Squeezars observable in Galactic Squeezars observable in Galactic CenterCenter
Tidally captured stars around IBHs Tidally captured stars around IBHs may be the engine that powers ULXsmay be the engine that powers ULXs
LISA stars will be highly eccentricLISA stars will be highly eccentric