Gravitational Wave Sources From Dense Star Clusters Cole Miller University of Maryland

Outline Detection of gravitational radiation. Sources in stellar clusters. IMBH-IMBH mergers? Sources in galactic nuclei. Extreme mass ratio inspirals. Tidal separation of binaries. IMBH-SMBH mergers.

Gravitational Wave Detectors

GW Sources in Clusters NS-NS merger: rate small compared to disk. NS-BH, BH-BH: could be important because of unique formation channels. IMBH-BH? Visible only to small distances with LISA.

NS-NS merger rate From Kim et al >10 -5 /yr at 99% conf

LISA Detection Distance: 1 yr from merger Will (2004)

IMBH-IMBH in Cluster Stellar collisions, evol --> IMBH? See Freitag talk. Can more than one IMBH form in cluster? Gurkan, Fregeau, Rasio, in prep. If so, visible to great distance. Could be LISA and LIGO sources!

Likelihood of IMBH-IMBH? M sun to Msun visible to Gpc with AdLIGO (Ilya Mandel) Total volume: few x Mpc 3 Similar for LISA (Will 2004) SF rate at z~0.5: ~10 -2 M sun /Mpc 3 /yr. Fraction in super star clusters: few x 10%. If M cluster ~10 5 M sun, ~10 3 clusters/yr formed in this volume. If >0.1% of clusters have IMBH-IMBH, interesting rate!

“Madau Plot”: Star Formation Rate

GW Sources in Galactic Nuclei M(<few pc)~  M glob Escape velocity much higher than globulars. Retain binaries, facilitate mergers? Merger of stellar clusters with nucleus. Fresh supply of binaries. Muno et al IMBHs as well?

Extreme Mass Ratio Inspirals BH-SMBH or IMBH-SMBH. Goal: simple mapping of SMBH spacetime. BH-SMBH uncertainties: Number density of 10 6 M sun SMBH. Rate of (1) merger, (2) detection w/ LISA.

Binary Tidal Separation by SMBH Previously, EMRIs considered by capture of single object due to gravitational radiation. But if BH in binary, pericenter distance can be much greater, hence cross section higher. Miller, Freitag, Hamilton, Lauburg (2005) Separation by IMBH in clusters? Pfahl (2005) Circularized orbits, no perturbation to plunge. Key: calculation of binary fraction and properties.

Single-body capture: distant view K. Gultekin

Single-body capture: close-up K. Gultekin

Binary Tidal Separation by SMBH Previously, EMRIs considered by capture of single object due to gravitational radiation. But if BH in binary, pericenter distance can be much greater, hence cross section higher. Miller, Freitag, Hamilton, Lauburg (2005) Separation by IMBH in clusters? Pfahl (2005) Circularized orbits, no perturbation to plunge. Key: calculation of binary fraction and properties.

Binary separation: close-up V. Lauburg

Binary separation: distant view V. Lauburg

Binary Tidal Separation by SMBH Previously, EMRIs considered by capture of single object due to gravitational radiation. But if BH in binary, pericenter distance can be much greater, hence cross section higher. Miller, Freitag, Hamilton, Lauburg (2005) Separation by IMBH in clusters? Pfahl (2005) Circularized orbits, no perturbation to plunge. Key: calculation of binary fraction and properties.

IMBH-SMBH Mergers If cluster with IMBH sinks to center, IMBH likely to merge with SMBH later. Signal strong enough to detect easily, but still is EMRI. Rate? Properties of orbits?

IMBH-SMBH Merger Sequence

Conclusions High density in clusters produces many potentially detectable GW sources. BH-BH, BH-IMBH, IMBH-IMBH, IMBH-SMBH. Continued input from N-body community is essential!