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Register a new userMerging stellar and intermediate-mass black holes in dense clusters: implications for LIGO, LISA and the next generation of gravitational wave detectors
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Added by
Manuel Arca Sedda Dr.
Publication date
2020
fields
Physics
and research's language is
English
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We study the formation of intermediate-mass ratio inspirals (IMRIs) triggered by the interactions between two stellar black holes (BHs) and an intermediate-mass BH (IMBH) inhabiting the centre of a dense star cluster. We exploit $N$-body models varying the IMBH mass, the stellar BH mass spectrum, and the star cluster properties. These simulations are coupled with a semi-analytic procedure to characterise the evolution of the remnant IMBH. The IMRIs formation probability attains values $sim 5-50%$, with larger values corresponding to larger IMBH masses. IMRIs map out the stellar BH mass spectrum, thus they might be used to unravel BH populations in star clusters harboring an IMBH. After the IMRI phase, an IMBH initially nearly maximal(almost non-rotating) tends to decrease(increase) its spin. If IMBHs grow mostly via repeated IMRIs, we show that only IMBH seeds sufficiently massive ($M_{rm seed} > 300$ M$_odot$) can grow up to $M_{rm imbh} >10^3$ M$_odot$ in dense globular clusters. Assuming that these seeds form at a redshift $zsim 2-6$, we find that around $1-5%$ of them would reach masses $sim 500-1500$ M$_odot$ at redshift $z=0$ and would exhibit low-spins, $S_{rm imbh} < 0.2$. Measuring the mass and spin of IMBHs involved in IMRIs could help unravelling their formation mechanisms. We show that LISA can detect IMBHs in Milky Way globular clusters with a signal-to-noise ratio SNR$=10-100$, or in the Large Magellanic Cloud with an SNR$=8-40$. We provide the IMRIs merger rate for LIGO ($Gamma_{rm LIG} = 0.003-1.6$ yr$^{-1}$), LISA ($Gamma_{rm LIS} = 0.02-60$ yr$^{-1}$), ET ($Gamma_{rm ET} = 1-600$ yr$^{-1}$), and DECIGO ($Gamma_{rm DEC} = 6-3000$ yr$^{-1}$). Our simulations show that IMRIs mass and spin encode crucial insights on the mechanisms that regulate IMBH formation and that the synergy among different detectors would enable us to fully unveil them. (Abridged)
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Intermediate mass black holes (IMBHs) with a mass between $10^{2}$ and $10^{5}$ times that of the sun, which bridges the {mass gap between the} stellar-mass black holes and the supermassive black holes, are crucial in understanding the evolution of the black holes. Although they are widely believed to exist, decisive evidence has long been absent. Motivated by the successful detection of massive stellar-mass black holes by advanced LIGO, through the gravitational wave radiation during the binary merger, in this work we investigate the prospect of detecting/identifying the lightest IMBHs (LIMBHs; the black holes $gtrsim 100M_odot$) with the second generation gravitational wave detectors. In general, the chance of hearing the birth of the LIMBHs is significantly higher than that to identify pre-merger IMBHs. The other formation channel of LIMBHs, where stars with huge mass/low-metallicity directly collapse, is likely silent, so the merger-driven birth of the LIMBHs may be the only observable scenario in the near future. Moreover, the prospect of establishing the presence of (lightest) intermediate mass black holes in the O3 run and beyond of advanced LIGO is found quite promising, implying that such an instrument could make another breakthrough on astronomy in the near future. The joining of other detectors like advanced Virgo would only increase the detection rate.
Massive young clusters (YCs) are expected to host intermediate-mass black holes (IMBHs) born via runaway collapse. These IMBHs are likely in binaries and can undergo mergers with other compact objects, such as stellar mass black holes (BHs) and neutron stars (NSs). We derive the frequency of such mergers starting from information available in the Local Universe. Mergers of IMBH-NS and IMBH-BH binaries are sources of gravitational waves (GWs), which might allow us to reveal the presence of IMBHs. We thus examine their detectability by current and future GW observatories, both ground- and space-based. In particular, as representative of different classes of instruments we consider Initial and Advanced LIGO, the Einstein gravitational-wave Telescope (ET) and the Laser Interferometer Space Antenna (LISA). We find that IMBH mergers are unlikely to be detected with instruments operating at the current sensitivity (Initial LIGO). LISA detections are disfavored by the mass range of IMBH-NS and IMBH-BH binaries: less than one event per year is expected to be observed by such instrument. Advanced LIGO is expected to observe a few merger events involving IMBH binaries in a 1-year long observation. Advanced LIGO is particularly suited for mergers of relatively light IMBHs (~100 Msun) with stellar mass BHs. The number of mergers detectable with ET is much larger: tens (hundreds) of IMBH-NS (IMBH-BH) mergers might be observed per year, according to the runaway collapse scenario for the formation of IMBHs. We note that our results are affected by large uncertainties, produced by poor observational constraints on many of the physical processes involved in this study, such as the evolution of the YC density with redshift.[abridged]
We propose a new formation channel for intermediate mass black hole (IMBH) binaries via globular cluster collisions in the Galactic disc. Using numerical simulations, we show that the IMBHs form a tight binary that enters the gravitational waves (GWs) emission dominated regime driven by stellar interactions, and ultimately merge in $lesssim 0.5$ Gyr. These events are clearly audible to LISA and can be associated with electromagnetic emission during the last evolutionary stages. During their orbital evolution, the IMBHs produce runaway stars comparable with GAIA and LAMOST observations.
The second generation of gravitational-wave detectors are being built and tuned all over the world. The detection of signals from binary black holes is beginning to fulfill the promise of gravitational-wave astronomy. In this work, we examine several possible configurations for third-generation laser interferometers in existing km-scale facilities. We propose a set of astrophysically motivated metrics to evaluate detector performance. We measure the impact of detector design choices against these metrics, providing a quantitative cost-benefit analyses of the resulting scientific payoffs.
Intermediate-mass black holes (IMBHs) could form via runaway merging of massive stars in a young massive star cluster (YMC). We combine a suite of numerical simulations of YMC formation with a semi-analytic model for dynamical friction and merging of massive stars and evolution of a central quasi-star, to predict how final quasi-star and relic IMBH masses scale with cluster properties (and compare with observations). The simulations argue that inner YMC density profiles at formation are steep (approaching isothermal), producing some efficient merging even in clusters with relatively low effective densities, unlike models which assume flat central profiles resembling those of globular clusters (GCs) {em after} central relaxation. Our results can be approximated by simple analytic scalings, with $M_{rm IMBH} propto v_{rm cl}^{3/2}$ where $v_{rm cl}^{2} = G,M_{rm cl}/r_{rm h}$ is the circular velocity in terms of initial cluster mass $M_{rm cl}$ and half-mass radius $r_{rm h}$. While this suggests IMBH formation is {em possible} even in typical clusters, we show that predicted IMBH masses for these systems are small, $sim 100-1000,M_{odot}$ or $sim 0.0003,M_{rm cl}$, below even the most conservative observational upper limits in all known cases. The IMBH mass could reach $gtrsim 10^{4},M_{odot}$ in the centers nuclear star clusters, ultra-compact dwarfs, or compact ellipticals, but in all these cases the prediction remains far below the present observed supermassive BH masses in these systems.
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