The Swansong of Stars The Swansong of Stars Orbiting Massive Black Orbiting Massive Black

HolesHolesClovis HopmanClovis Hopman

Weizmann Institute of ScienceWeizmann Institute of ScienceIsraelIsrael

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

4/7 r

The stellar cusp near a BHThe stellar cusp near a BH

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

How to get near a Massive How to get near a Massive BHBH

Race between inspiral and scattering

Alexander & Hopman,ApJL 2003

Radius of influence

Inspiral radius

Collision radius

Squeezars: Tidal PowerSqueezars: Tidal Power

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)

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

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

Gravitational Wave Gravitational Wave RadiationRadiation

Barack & Cutler, PRD 2004

Eccentricity of LISA starsEccentricity of LISA stars

Monte Carlo tracks in phase Monte Carlo tracks in phase spacespace

Hopman & Alexander, in prep.

LISA Stars in the Strong Gravity LISA Stars in the Strong Gravity RegimeRegime

Hopman & Alexander, in prep.

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

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