Gravitational Wave SourcesFrom 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

http://www.srl.caltech.edu/lisa/graphics/05.LIGO.LISA.jpg

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 rateFrom Kim et al. 2004>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?• 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!

“Madau Plot”: Star Formation Rate

GW Sources in Galactic Nuclei

• M(<few pc)~Mglob

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?

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.

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!