Black hole and neutron star mergers in galactic nuclei

Fragione, Giacomo; Grishin, Evgeni; Leigh, Nathan W. C.; Perets, Hagai B.; Perna, Rosalba

doi:10.1093/mnras/stz1651

Cited by 177 publications

(134 citation statements)

References 158 publications

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“…A possible way to distinguish GW captures from the other channels is their high eccentricity in the LIGO frequency range (e > 0.1 at f > 10 Hz). However, eccentric mergers can also be produced in triple systems where a BH binary achieves extreme eccentricity through interaction with with a third body; those systems could be • A binary BH orbiting around a SMBH in a galactic center can experience variations of inclination and eccentricity due to Kozai-Lidov effect, sometimes reaching e > 0.9999 which quickly leads to coalescence through GW energy loss (Antonini & Perets 2012;Fragione et al 2019;Hamers et al 2018;Hoang et al 2018).…”

Section: Discussionmentioning

confidence: 99%

The Rate of Stellar Mass Black Hole Scattering in Galactic Nuclei

Rasskazov

Kocsis

2019

ApJ

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We consider a black hole (BH) density cusp in a nuclear star cluster (NSC) hosting a supermassive back hole (SMBH) at its center. Assuming the stars and BHs inside the SMBH sphere of influence are mass-segregated, we calculate the number of BHs that sink into this region under the influence of dynamical friction. We find that the total number of BHs increases significantly in this region due to this process for lower mass SMBHs by up to a factor of 5, but there is no increase in the vicinity of the highest mass SMBHs. Due to the high BH number density in the NSC, BH-BH binaries form during close approaches due to GW emission. We update the previous estimate of O'Leary et al. for the rate of such GW capture events by estimating the n 2 / n 2 parameter where n is the number density. We find a BH merger rate for this channel to be in the range ∼ 0.002 − 0.04 Gpc −3 yr −1 . The total merger rate is dominated by the smallest galaxies hosting SMBHs, and the number of heaviest BHs in the NSC. It is also exponentially sensitive to the radial number density profile exponent, reaching > 100 Gpc −3 yr −1 when the BH mass function is m −2.3 or shallower and the heaviest BH radial number density is close to r −3 . Even if the rate is much lower than the range constrained by the current LIGO detections, the GW captures around SMBHs can be distinguished by their high eccentricity in the LIGO band.

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Section: Discussionmentioning

confidence: 99%

The Rate of Stellar Mass Black Hole Scattering in Galactic Nuclei

Rasskazov

Kocsis

2019

ApJ

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“…The tool does not take into account the metallicity gradient in modeling BBH galaxy hosts, although this issue is partly addressed via defining different metallicity distribution choices (see, for instance, models ID 2a, b, and c). Our analysis excludes BBH mergers forming via alternative processes, like BBH formation around an SMBH or in an AGN disk (McKernan et al 2012(McKernan et al , 2014(McKernan et al , 2018Bartos et al 2017;Yang et al 2019), or in triples (Antonini & Perets 2012;Fragione et al 2019;Hoang et al 2018;Arca Sedda 2020). Moreover, our tool does not account for chemically homogeneous binary evolution (Marchant et al 2016).…”

Section: Caveatsmentioning

confidence: 99%

Fingerprints of Binary Black Hole Formation Channels Encoded in the Mass and Spin of Merger Remnants

Sedda¹,

Mapelli

Spera

et al. 2020

ApJ

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Binary black holes (BBHs) are thought to form in different environments, including the galactic field and (globular, nuclear, young, and open) star clusters. Here, we propose a method to estimate the fingerprints of the main BBH formation channels associated with these different environments. We show that the metallicity distribution of galaxies in the local universe along with the relative amount of mergers forming in the field or in star clusters determine the main properties of the BBH population. Our fiducial model predicts that the heaviest merger to date, GW170729, originated from a progenitor that underwent 2-3 merger events in a dense star cluster, possibly a galactic nucleus. The model predicts that at least one merger remnant out of a hundred BBH mergers in the local universe has mass <  M M 90 110 rem  , and one in a thousand can reach a mass as large as  M M 250 rem . Such massive black holes would bridge the gap between stellar-mass and intermediate-mass black holes. The relative number of low-and high-mass BBHs can help us unravel the fingerprints of different formation channels. Based on the assumptions of our model, we expect that isolated binaries are the main channel of BBH merger formation if~70% of the whole BBH population has remnants with masses < M 50  , whereas 6% of remnants having masses > M 75  points to a significant subpopulation of dynamically formed BBH binaries.

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“…(BHs;Abbott et al 2019), it is crucial to understand the origin of stellar-mass BHs. Alongside dynamical (Di Carlo et al 2019;Fragione et al 2019) as well as primordial (Nishikawa et al 2019) formation pathways, one of the proposed channels for double-BH formation is close binary evolution (e.g. Belczynski et al 2002;Mandel & de Mink 2016;Marchant et al 2016;Abdul-Masih et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Is HR 6819 a triple system containing a black hole?

Bodensteiner

Shenar

Mahy

et al. 2020

A&A

106

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Context. HR 6819 was recently proposed to be a triple system consisting of an inner B-type giant plus black hole (BH) binary with an orbital period of 40 d and an outer Be tertiary. This interpretation is mainly based on two inferences: that the emission attributed to the outer Be star is stationary and that the inner star, which is used as mass calibrator for the BH, is a B-type giant. Aims. We re-investigate the properties of HR 6819 to search for a possibly simpler alternative explanation for HR 6819, which does not invoke the presence of a triple system with a BH in the inner binary. Methods. Based on an orbital analysis, the disentangling of the spectra of the two visible components and the atmosphere analysis of the disentangled spectra, we investigate the configuration of the system and the nature of its components. Results. Disentangling implies that the Be component is not a static tertiary, but rather a component of the binary in the 40 d orbit. The inferred radial velocity amplitudes of K1 = 60.4 ± 1.0 km s−1 for the B-type primary and K2 = 4.0 ± 0.8 km s−1 for the Be-type secondary imply an extreme mass ratio of M2/M1 = 15 ± 3. We find that the B-type primary, which we estimate to contribute about 45% to the optical flux, has an effective temperature of Teff = 16 ± 1 kK and a surface gravity of log g = 2.8 ± 0.2 [cgs], while the Be secondary, which contributes about 55% to the optical flux, has Teff = 20 ± 2 kK and log g = 4.0 ± 0.3 [cgs]. We infer spectroscopic masses of 0.4−0.1+0.3and 6−3+5 for the primary and secondary which agree well with the dynamical masses for an inclination of i = 32°. This indicates that the primary might be a stripped star rather than a B-type giant. Evolutionary modelling suggests that a possible progenitor system would be a tight (Pi ≈ 2 d) B+B binary system that experienced conservative mass transfer. While the observed nitrogen enrichment of the primary conforms with the predictions of the evolutionary models, we find no indications for the predicted He enrichment. Conclusions. We suggest that HR 6819 is a binary system consisting of a stripped B-type primary and a rapidly-rotating Be star that formed from a previous mass-transfer event. In the framework of this interpretation, HR 6819 does not contain a BH. Interferometry can distinguish between these two scenarios by providing an independent measurement of the separation between the visible components.

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Black hole and neutron star mergers in galactic nuclei

Cited by 177 publications

References 158 publications

The Rate of Stellar Mass Black Hole Scattering in Galactic Nuclei

The Rate of Stellar Mass Black Hole Scattering in Galactic Nuclei

Fingerprints of Binary Black Hole Formation Channels Encoded in the Mass and Spin of Merger Remnants

Is HR 6819 a triple system containing a black hole?

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