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Register a new userThe implications of high BH spins on the origin of BH-BH mergers
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The LIGO/Virgo collaboration has reported 50 BH-BH mergers and 8 additional candidates recovered from digging deeper into the detectors noise. Majority of these mergers have low effective spins pointing toward low BH spins and efficient angular momentum transport in massive stars as proposed by several models (e.g., Tayler-Spruit magnetic dynamo or Fuller model). However, out of these 58 mergers, 7 are consistent with having high effective spin parameter (chi_eff>0.3). Additionally, 2 out of these 7 events seem to have high effective spins sourced from the high spin of a primary (more massive) BH. The most extreme merger has very high primary BH dimensionless spin (a_1=0.9). These particular observations may be potentially used to discriminate between the isolated binary and dynamical globular cluster BH-BH formation channels. It may seem that high BH spins point to the dynamical origin if stars have efficient angular momentum transport and form low-spinning BHs. Then dynamical formation is required to produce second and third generations of BH-BH mergers that typically produce high-spinning BHs. Here we show that isolated binary BH-BH formation channel can naturally reproduce such highly spinning BHs. Our models start with efficient angular momentum transport in massive stars that is needed to reproduce majority of BH-BH mergers with low effective spins. However, some massive binaries are subject to strong tidal spin-up allowing for the formation of moderate fraction (~10%) of BH-BH mergers with high effective spins (chi_eff>0.4-0.5). Moreover, binary evolution can produce small fraction (~1%) of BH-BH mergers with almost maximally spinning primary BHs ($a_1>0.9$). Therefore, the formation scenario of those unusual BH-BH mergers remains unresolved.
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The gravitational-wave detection by the LIGO-Virgo scientific collaboration shows that the black hole and neutron star (BH-NS) or BH-BH systems with a BH mass of tens of solar masses widely exist in the universe. Two main types of scenarios have been invoked for the formation of BH-NS/BH systems, including isolated binary evolution in galactic fields and dynamical interactions in dense environments. Here we propose that if the BH-NS/BH systems are formed from isolated binary evolution, the supernova (SN) signal associated with the second core collapse would show some identifiable features, due to the accretion feedback from the companion BH. Depending on the binary properties, we show that the SN lightcurve could present a sharp peak around $sim10$ days, with luminosity even at the level of the super luminous SNe ( e.g. $sim10^{44}~rm erg~s^{-1}$) or present a plateau feature lasting for several tens of days with regular luminosity of core collapse SNe. Comparing the event rate density of these special SN signals with the event rate density of LIGO-Virgo detected BH-NS/BH systems could help to distinguish the BH-NS/BH formation channel.
The next generation of ground-based gravitational wave detectors may detect a few mergers of comparable-mass Msimeq 100-1000 Msun (intermediate-mass, or IMBH) spinning black holes. Black hole spin is known to have a significant impact on the orbit, merger signal, and post-merger ringdown of any binary with non-negligible spin. In particular, the detection volume for spinning binaries depends significantly on the component black hole spins. We provide a fit to the single-detector and isotropic-network detection volume versus (total) mass and arbitrary spin for equal-mass binaries. Our analysis assumes matched filtering to all significant available waveform power (up to l=6 available for fitting, but only l<= 4 significant) estimated by an array of 64 numerical simulations with component spins as large as S_{1,2}/M^2 <= 0.8. We provide a spin-dependent estimate of our uncertainty, up to S_{1,2}/M^2 <= 1. For the initial (advanced) LIGO detector, our fits are reliable for $Min[100,500]M_odot$ ($Min[100,1600]M_odot$). In the online version of this article, we also provide fits assuming incomplete information, such as the neglect of higher-order harmonics. We briefly discuss how a strong selection bias towards aligned spins influences the interpretation of future gravitational wave detections of IMBH-IMBH mergers.
While an axion-clouded black hole (BH) encounters a pulsar (PSR) or has a PSR companion, a gravitational molecule can be formed. In such a system, the axion cloud evolves at the binary hybrid orbitals, as it happens at microscopic level to electron cloud in a chemical molecule. To demonstrate this picture, we develop a semi-analytical formalism using the method of linear combination of atomic orbitals with an adiabatic approximation. An oscillating axion-cloud profile and a perturbed binary rotation, together with unique and novel detection signals, are then predicted. Remarkably, the proposed PSR timing and polarization observables, namely the oscillation of periastron time shift and the birefringence with multiple modulations, correlate in pattern, and thus can be properly combined to strengthen the detection.
Anisotropy of gravitational wave (GW) emission results in a net momentum gained by the black hole (BH) merger product, leading to a recoil velocity up to $sim10^3text{ km s}^{-1}$, which may kick it out of a globular cluster (GC). We estimate GW kick retention fractions of merger products assuming different models for BH spin magnitude and orientation (MS0 - random, MS1 - spin as a function of mass and metalicity, MS2 - constant value of $0.5$). We check how they depend on BH-BH merger time and properties of the cluster. We analyze the implications of GW kick retention fractions on intermediate massive BH (IMBH) formation by repeated mergers in a GC. We also calculate final spin of the merger product, and investigate how it correlates with effective spin of the binary. We used data from MOCCA (MOnte Carlo Cluster simulAtor) GC simulations to get a realistic sample of BH-BH mergers, assigned each BH spin value according to a studied model, and calculated recoil velocity and final spin based on most recent theoretical formulas. We discovered that for physically motivated models, GW kick retention fractions are about $30%$ and display small dependence on assumptions about spin, but are much more prone to cluster properties. In particular, we discovered a strong dependence of GW kick retention fractions on cluster density. We also show that GW kick retention fractions are high in final life stages of the cluster, but low at the beginning. Finally, we derive formulas connecting final spin with effective spin for primordial binaries, and with maximal effective spin for dynamical binaries.
Supermassive black holes (BHs) obey tight scaling relations between their mass and their host galaxy properties such as total stellar mass, velocity dispersion, and potential well depth. This has led to the development of self-regulated models for BH growth, in which feedback from the central BH halts its own growth upon reaching a critical threshold. However, models have also been proposed in which feedback plays no role: so long as a fixed fraction of the host gas supply is accreted, relations like those observed can be reproduced. Here, we argue that the scatter in the observed BH-host correlations, and its run with scale, presents a demanding constraint on any model for these correlations, and that it favors self-regulated models of BH growth. We show that the scatter in the stellar mass fraction within a radius R in observed ellipticals and spheroids increases strongly at small R. At fixed total stellar mass (or host velocity dispersion), on very small scales near the BH radius of influence, there is an order-of-magnitude scatter in the amount of gas that must have entered and formed stars. In short, the BH appears to know more about the global host galaxy potential on large scales than the stars and gas supply on small scales. This is predicted in self-regulated models; however, models where there is no feedback would generically predict order-of-magnitude scatter in the BH-host correlations. Likewise, models in which the BH feedback in the bright mode does not regulate the growth of the BH itself, but sets the stellar mass of the galaxy by inducing star formation or blowing out a mass in gas much larger than the galaxy stellar mass, are difficult to reconcile with the scatter on small scales.
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