The Swansong of Stars Orbiting Massive Black Holes Clovis Hopman Weizmann Institute of Science Israel Advisor: Tal Alexander
Dissipative stellar processes near Massive Black Holes Tidally powered stars in the Galactic Center Ultraluminous X-ray sources Gravitational Wave Radiation
The stellar cusp near a BH
Tides and Gravity Waves Tides GWR
How to get near a Massive BH
Race between inspiral and scattering Alexander & Hopman, Ap. JL 2003
Radius of influence Inspiral radius Collision radius
Squeezars: Tidal Power
Surviving tidal heating Squeezars in Galactic Centers are transient sources Survival: low mass MBHs and efficient cooling
Squeezars Stars powered by tidal “squeezing” Squeezars observable in Galactic Center (Alexander & Morris, Ap. JL 2003) ~ 1 squeezar in GC (Alexander & Hopman, Ap. JL 2003) Squeezars evaporate near MBHs
Ultraluminous X-ray Sources Super Eddington luminosities IBH: engine of ULX? IBH can be formed dynamically in cluster (Portegies Zwart et al. , Nature 2004)
What feeds the IBH? ? Clusters contain too little gas Tidal disruption of star gives only short (~yr) flare (Rees, Nature 1988) Solution: Tidal Capture!
ULX: IBH fed by a tidally captured star Circularization possible around IBH Roche lobe overflow supplies gas ULX can switch on after cluster evaporates Lifetime and luminosity as observed
Circularization Hopman, Portegies Zwart & Alexander, Ap. JL 2004
Captured Stars Probability = Capture Rate Stellar Lifetime 10 % Rate independent of relaxation time Hopman, Portegies Zwart & Alexander, Ap. JL 2004
Mass Transfer and Luminosity Hopman, Portegies Zwart & Alexander, Ap. JL 2004
Gravitational Wave Radiation
Eccentricity of LISA stars Barack & Cutler, PRD 2004
Monte Carlo tracks in phase space Hopman & Alexander, in prep.
LISA Stars in the Strong Gravity Regime Massive Black Holes: Intermediate Mass Black Holes: Hopman & Alexander, in prep.
Mass segregation: Heavy stars closer to MBH! Rate independent of relaxation time Orbits are very eccentric Probably no signal from IBHs
Conclusions Squeezars observable in Galactic Center Tidally captured stars around IBHs may be the engine that powers ULXs LISA stars will be highly eccentric
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