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Gravitational Wave Sources From Dense Star Clusters

Gravitational Wave Sources From Dense Star Clusters. Cole Miller University of Maryland. Outline. Detection of gravitational radiation. Sources in stellar clusters. IMBH-IMBH mergers?

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Gravitational Wave Sources From Dense Star Clusters

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  1. Gravitational Wave SourcesFrom Dense Star Clusters Cole Miller University of Maryland

  2. 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.

  3. Gravitational Wave Detectors http://www.srl.caltech.edu/lisa/graphics/05.LIGO.LISA.jpg

  4. 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.

  5. NS-NS merger rate From Kim et al. 2004 >10-5/yr at 99% conf

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

  7. 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!

  8. Likelihood of IMBH-IMBH? • 50 - 50 Msun to 200 - 200 Msun visible to 2.5-3 Gpc with AdLIGO (Ilya Mandel) Total volume: few x 1010 Mpc3 Similar for LISA (Will 2004) • SF rate at z~0.5: ~10-2 Msun/Mpc3/yr. • Fraction in super star clusters: few x 10%. • If Mcluster~105 Msun, ~103 clusters/yr formed in this volume. • If >0.1% of clusters have IMBH-IMBH, interesting rate!

  9. “Madau Plot”: Star Formation Rate

  10. GW Sources in Galactic Nuclei • M(<few pc)~SMglob Escape velocity much higher than globulars. Retain binaries, facilitate mergers? • Merger of stellar clusters with nucleus. Fresh supply of binaries. Muno et al. 2005 IMBHs as well?

  11. Extreme Mass Ratio Inspirals • BH-SMBH or IMBH-SMBH. • Goal: simple mapping of SMBH spacetime. • BH-SMBH uncertainties: Number density of 106 Msun SMBH. Rate of (1) merger, (2) detection w/ LISA.

  12. 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.

  13. Single-body capture: distant view K. Gultekin

  14. Single-body capture: close-up K. Gultekin

  15. 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.

  16. Binary separation: close-up V. Lauburg

  17. Binary separation: distant view V. Lauburg

  18. 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.

  19. 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?

  20. IMBH-SMBH Merger Sequence

  21. 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!

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