arXiv subjects

K. Belczynski

Publications and source records attributed to K. Belczynski.

At least 37 records · Page 2Linked to original sources

arXiv2018

MOCCA-SURVEY Database I: Assessing GW kick retention fractions for BH-BH mergers in globular clusters

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 $\sim10^3\text{ km s}^{-1}$, 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.

astro-ph.GA↗

arXiv2018

Explaining LIGO's observations via isolated binary evolution with natal kicks

We compare binary evolution models with different assumptions about black-hole natal kicks to the first gravitational-wave observations performed by the LIGO detectors. Our comparisons attempt to reconcile merger rate, masses, spins, and spin-orbit misalignments of all current observations with state-of-the-art formation scenarios of binary black holes formed in isolation. We estimate that black holes (BHs) should receive natal kicks at birth of the order of $σ\simeq 200$ (50) km/s if tidal processes do (not) realign stellar spins. Our estimate is driven by two simple factors. The natal kick dispersion $σ$ is bounded from above because large kicks disrupt too many binaries (reducing the merger rate below the observed value). Conversely, the natal kick distribution is bounded from below because modest kicks are needed to produce a range of spin-orbit misalignments. A distribution of misalignments increases our models' compatibility with LIGO's observations, if all BHs are likely to have natal spins. Unlike related work which adopts a concrete BH natal spin prescription, we explore a range of possible BH natal spin distributions. Within the context of our models, for all of the choices of $σ$ used here and within the context of one simple fiducial parameterized spin distribution, observations favor low BH natal spin.

astro-ph.HE↗

arXiv2018

The origin of the first neutron star -- neutron star merger

The first neutron star-neutron star (NS-NS) merger was discovered on August 17, 2017 through gravitational waves (GW170817) and followed with electromagnetic observations. This merger was detected in an old elliptical galaxy with no recent star formation. We perform a suite of numerical calculations to understand the formation mechanism of this merger. We probe three leading formation mechanisms of double compact objects: classical isolated binary star evolution, dynamical evolution in globular clusters and nuclear cluster formation to test whether they are likely to produce NS-NS mergers in old host galaxies. Our simulations with optimistic assumptions show current NS-NS merger rates at the level of 10^-2 yr^-1 from binary stars, 5 x 10^-5 yr^-1 from globular clusters and 10^-5 yr^-1 from nuclear clusters for all local elliptical galaxies (within 100 Mpc^3). These models are thus in tension with the detection of GW170817 with an observed rate 1.5 yr^-1 (per 100 Mpc^3; LIGO/Virgo estimate). Our results imply that either (i) the detection of GW170817 by LIGO/Virgo at their current sensitivity in an elliptical galaxy is a statistical coincidence; or that (ii) physics in at least one of our three models is incomplete in the context of the evolution of stars that can form NS-NS mergers; or that (iii) another very efficient (unknown) formation channel with a long delay time between star formation and merger is at play.

astro-ph.HE↗

arXiv2016

The occurrence of Binary Evolution Pulsators in the classical instability strip of RR Lyrae and Cepheid variables

Single star evolution does not allow extremely low-mass stars to cross the classical instability strip (IS) during the Hubble time. However, within binary evolution framework low-mass stars can appear inside the IS once the mass transfer (MT) is taken into account. Triggered by a discovery of low-mass 0.26 Msun RR Lyrae-like variable in a binary system, OGLE-BLG-RRLYR-02792, we investigate the occurrence of similar binary components in the IS, which set up a new class of low-mass pulsators. They are referred to as Binary Evolution Pulsators (BEPs) to underline the interaction between components, which is crucial for substantial mass loss prior to the IS entrance. We simulate a population of 500 000 metal-rich binaries and report that 28 143 components of binary systems experience severe MT (loosing up to 90% of mass), followed by at least one IS crossing in luminosity range of RR Lyrae (RRL) or Cepheid variables. A half of these systems enter the IS before the age of 4 Gyr. BEPs display a variety of physical and orbital parameters, with the most important being the BEP mass in range 0.2-0.8 Msun, and the orbital period in range 10-2500 d. Based on the light curve only, BEPs can be misclassified as genuine classical pulsators, and as such they would contaminate genuine RRL and classical Cepheid variables at levels of 0.8% and 5%, respectively. We state that the majority of BEPs will remain undetected and we discuss relevant detection limitations.

astro-ph.SR↗

arXiv2016

On the likelihood of detecting gravitational waves from Population III compact object binaries

We study the contribution of binary black hole (BH-BH) mergers from the first, metal-free stars in the Universe (Pop III) to gravitational wave detection rates. Our study combines initial conditions for the formation of Pop III stars based on N-body simulations of binary formation (including rates, binary fraction, initial mass function, orbital separation and eccentricity distributions) with an updated model of stellar evolution specific for Pop III stars. We find that the merger rate of these Pop III BH-BH systems is relatively small (< 0.1 Gpc^-3 yr^-1) at low redshifts (z<2), where it can be compared with the LIGO empirical estimate of 9-240 Gpc^-3 yr^-1 (Abbott et al. 2016). The predicted rates are even smaller for Pop III double neutron star and black hole neutron star mergers. Our rates are compatible with those of Hartwig et al. (2016), but significantly smaller than those found in previous work (Bond & Carr 1984; Belczynski et al. 2004; Kinugawa et al. 2014, 2016). We explain the reasons for this discrepancy by means of detailed model comparisons and point out that (i) identification of Pop III BH-BH mergers may not be possible by advanced LIGO, and (ii) the level of stochastic gravitational wave background from Pop III mergers may be lower than recently estimated (Kowalska et al. 2012; Inayoshi et al. 2016; Dvorkin et al. 2016). We further estimate gravitational wave detection rates for third-generation interferometric detectors. Our calculations are relevant for low to moderately rotating Pop III stars. We can now exclude significant (> 1 per cent) contribution of these stars to low-redshift BH-BH mergers. However, it remains to be tested whether (and at what level) rapidly spinning Pop III stars (homogeneous evolution) can contribute to BH-BH mergers in the local Universe.

astro-ph.HE↗

arXiv2016

The Effect of Pair-Instability Mass Loss on Black Hole Mergers

Mergers of two stellar origin black holes are a prime source of gravitational waves and are under intensive investigations. One crucial ingredient in their modeling has so far been neglected. Pair-instability pulsation supernovae with associated severe mass loss may suppress formation of massive black holes, decreasing black hole merger rates for the highest black hole masses. The mass loss associated with pair-instability pulsation supernovae limits the Population I/II stellar-origin black hole mass to 50 Msun, in tension with earlier predictions that the maximum black hole mass could be as high as 100 Msun. Suppression of double black hole merger rates by pair-instability pulsation supernovae is negligible for our evolutionary channel. Our standard evolutionary model with inclusion of pair-instability pulsation supernovae and with pair-instability supernovae is fully consistent with the LIGO detections of black hole mergers: GW150914, GW151226 and LVT151012. The LIGO observations seem to exclude high (>400 km/s) BH natal kicks. We predict the detection of several up to 60 BH-BH mergers with total mass 10--150 Msun (most likely range: 20--80 Msun) in the forthcoming 60 effective days of LIGO O2 observations.

astro-ph.HE↗

arXiv2016

Stability of mass transfer from massive giants: double black-hole binary formation and ultra-luminous X-ray sources

The mass transfer in binaries with massive donors and compact companions, when the donors rapidly evolve after their main sequence, is one of the dominant formation channels of merging double stellar-mass black hole binaries. This mass transfer was previously postulated to be unstable and was expected to lead to a common envelope event. The common envelope event then would end with either double black hole formation, or with the merger of the two stars. We re-visit the stability of this mass transfer, and find that for a large range of the binary orbital separations this mass transfer is stable. This newly found stability allows us to reconcile the theoretical rate for double black hole binary mergers predicted by population synthesis studies, and the empirical rate obtained by LIGO. Futhermore, the stability of the mass transfer leads to the formation of ultra-luminous X-ray sources. The theoretically predicted formation rates of ultra-luminous X-ray sources powered by a stellar-mass BH, as well as the range of produced X-ray luminosity, can explain the observed bright ultra-luminous X-ray sources.

astro-ph.HE↗

arXiv2016

P13 an ULX that is a potential progenitor of merging BH-NS system

We have studied the future evolution of a recently discovered ULX source P13 in NGC7793. This source was shown to contain a 5-15$M_{\odot}$ black hole and a massive 18-23$M_{\odot}$ B9Ia companion on a 64 day orbit. For low black hole mass (5-10$M_{\odot}$) and high companion mass $\gtrsim 20 M_{\odot}$ the binary is predicted to initiate a common envelope evolution in near future and significantly decrease the orbital separation (6 hr orbit). This leads to a high probability ($\sim70\%$) of the system surviving a supernova explosion that will form a neutron star out of the companion. About one third of the surviving BH-NS systems will merge within Hubble time and be a source of high frequency gravitational radiation. We estimate that the chances of detection of BH-NS systems with advanced LIGO/Virgo that form via P13-evolutionary channel are at the level of 0.1 yr$^{-1}$ with wide range of allowed probability $0 ÷0.6$yr$^{-1}$. This is the fourth empirical estimate of BH-NS merger rate.

astro-ph.HE↗

arXiv2015

SMC3 as a test to the binary evolution

SMC 3 is one of the most interesting symbiotic stars. This binary contains a bright K-type giant transferring mass to a massive white dwarf comanion, which makes it is a very promising SN Ia candidate. We discuss the evolutionary status of the system using results of population synthesis code.

astro-ph.SR↗

arXiv2015

Merger rates of double neutron stars and stellar origin black holes: The Impact of Initial Conditions on Binary Evolution Predictions

The initial mass function (IMF), binary fraction and distributions of binary parameters (mass ratios, separations and eccentricities) are indispensable input for simulations of stellar populations. It is often claimed that these are poorly constrained significantly affecting evolutionary predictions. Recently, dedicated observing campaigns provided new constraints on the initial conditions for massive stars. Findings include a larger close binary fraction and a stronger preference for very tight systems. We investigate the impact on the predicted merger rates of neutron stars and black holes. Despite the changes with previous assumptions, we only find an increase of less than a factor 2 (insignificant compared with evolutionary uncertainties of typically a factor 10-100). We further show that the uncertainties in the new initial binary properties do not significantly affect (within a factor of 2) our predictions of double compact object merger rates. An exception is the uncertainty in IMF (variations by a factor of 6 up and down). No significant changes in the distributions of final component masses, mass ratios, chirp masses and delay times are found. We conclude that the predictions are, for practical purposes, robust against uncertainties in the initial conditions concerning binary parameters with exception of the IMF. This eliminates an important layer of the many uncertain assumptions affecting the predictions of merger detection rates with the gravitational wave detectors aLIGO/aVirgo.

astro-ph.HE↗

arXiv2015

Cosmic Neutron Star Merger Rate and Gravitational Waves constrained by the R Process Nucleosynthesis

The cosmic evolution of the neutron star merger (NSM) rate can be deduced from the observed cosmic star formation rate. This allows to estimate the rate expected in the horizon of the gravitational wave detectors advanced Virgo and ad LIGO and to compare those rates with independent predictions. In this context, the rapid neutron capture process, or r process, can be used as a constraint assuming NSM is the main astrophysical site for this nucleosynthetic process. We compute the early cosmic evolution of a typical r process element, Europium. Eu yields from NSM are taken from recent nucleosynthesis calculations. The same approach allows to compute the cosmic rate of Core Collapse SuperNovae (CCSN) and the associated evolution of Eu. We find that the bulk of Eu observations at high iron abundance can be rather well fitted by either CCSN or NSM scenarios. However, at lower metallicity, the early Eu cosmic evolution favors NSM as the main astrophysical site for the r process. A comparison between our calculations and spectroscopic observations at very low metallicities allows to constrain the coalescence timescale in the NSM scenario to about 0.1 to 0.2 Gyr. These values are in agreement with the coalescence timescales of some observed binary pulsars. Finally, the cosmic evolution of Eu is used to put constraints on the NSM rate, the merger rate in the horizon of the gravitational wave detectors advanced Virgo/ad LIGO, as well as the expected rate of electromagnetic counterparts to mergers (kilonovae) in large near-infrared surveys.

astro-ph.HE↗

arXiv2015

Double Compact Objects III: Gravitational Wave Detection Rates

The unprecedented range of second-generation gravitational-wave (GW) observatories calls for refining the predictions of potential sources and detection rates. The coalescence of double compact objects (DCOs)---i.e., neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS), and black hole-black hole (BH-BH) binary systems---is the most promising source of GWs for these detectors. We compute detection rates of coalescing DCOs in second-generation GW detectors using the latest models for their cosmological evolution, and implementing inspiral-merger-ringdown (IMR) gravitational waveform models in our signal-to-noise ratio calculations. We find that: (1) the inclusion of the merger/ringdown portion of the signal does not significantly affect rates for NS-NS and BH-NS systems, but it boosts rates by a factor $\sim 1.5$ for BH-BH systems; (2) in almost all of our models BH-BH systems yield by far the largest rates, followed by NS-NS and BH-NS systems, respectively, and (3) a majority of the detectable BH-BH systems were formed in the early Universe in low-metallicity environments. We make predictions for the distributions of detected binaries and discuss what the first GW detections will teach us about the astrophysics underlying binary formation and evolution.

astro-ph.HE↗

arXiv2015

On the formation and evolution of the first Be star in a black hole binary MWC 656

We find that the formation of MWC 656 (the first Be binary containing a black hole) involves a common envelope phase and a supernova explosion. This result supports the idea that a rapidly rotating Be star can emerge out of a common envelope phase, which is very intriguing because this evolutionary stage is thought to be too fast to lead to significant accretion and spin up of the B star. We predict $\sim 10-100$ of B BH binaries to currently reside in the Galactic disk, among which around $1/3$ contain a Be star, but there is only a small chance to observe a system with parameters resembling MWC 656. If MWC 656 is representative of intrinsic Galactic Be BH binary population, it may indicate that standard evolutionary theory needs to be revised. This would pose another evolutionary problem in understanding BH binaries, with BH X-ray Novae formation issue being the prime example. The future evolution of MWC 656 with a $\sim 5$ M$_{\odot}$ black hole and with a $\sim 13$ M$_{\odot}$ main sequence companion on a $\sim 60$ day orbit may lead to the formation of a coalescing BH-NS system. The estimated Advanced LIGO/Virgo detection rate of such systems is up to $\sim 0.2$ yr$^{-1}$. This empirical estimate is a lower limit as it is obtained with only one particular evolutionary scenario, the MWC 656 binary. This is only a third such estimate available (after Cyg X-1 and Cyg X-3), and it lends additional support to the existence of so far undetected BH--NS binaries.

astro-ph.HE↗

arXiv2015

A Model of the Stochastic Gravitational-Wave Background due to Core Collapse to Black Holes

Superposition of gravitational waves generated by astrophysical sources is expected to give rise to the stochastic gravitational-wave background. We focus on the background generated by the ring-down of black holes produced in the stellar core collapse events across the universe. We systematically study the parameter space in this model, including the most recent information about the star formation rate and about the population of black holes as a function of redshift and of metallicity. We investigate the accessibility of this gravitational wave background to the upcoming gravitational-wave detectors, such as Advanced LIGO and Einstein Telescope.

gr-qc↗

arXiv2014

Effect of metallicity on the gravitational-wave signal from the cosmological population of compact binary coalescences

Recent studies on stellar evolution have shown that the properties of compact objects strongly depend on the metallicity of the environment in which they were formed. Using some very simple assumptions on the metallicity of the stellar populations, we explore how this property affects the unresolved gravitational-wave background from extragalactic compact binaries. We obtained a suit of models using population synthesis code, estimated the gravitational-wave background they produce, and discuss its detectability with second- (advanced LIGO, advanced Virgo) and third- (Einstein Telescope) generation detectors. Our results show that the background is dominated by binary black holes for all considered models in the frequency range of terrestrial detectors, and that it could be detected in most cases by advanced LIGO/Virgo, and with Einstein Telescope with a very high signal-to-noise ratio. The observed peak in a gravitational wave spectrum depends on the metallicity of the stellar population.

astro-ph.CO↗

arXiv2013

Modeling the Redshift Evolution of the Normal Galaxy X-ray Luminosity Function

Emission from X-ray binaries (XRBs) is a major component of the total X-ray luminosity of normal galaxies, so X-ray studies of high redshift galaxies allow us to probe the formation and evolution of X-ray binaries on very long timescales. In this paper, we present results from large-scale population synthesis models of binary populations in galaxies from z = 0 to 20. We use as input into our modeling the Millennium II Cosmological Simulation and the updated semi-analytic galaxy catalog by Guo et al. (2011) to self-consistently account for the star formation history (SFH) and metallicity evolution of each galaxy. We run a grid of 192 models, varying all the parameters known from previous studies to affect the evolution of XRBs. We use our models and observationally derived prescriptions for hot gas emission to create theoretical galaxy X-ray luminosity functions (XLFs) for several redshift bins. Models with low CE efficiencies, a 50% twins mass ratio distribution, a steeper IMF exponent, and high stellar wind mass loss rates best match observational results from Tzanavaris & Georgantopoulos (2008), though they significantly underproduce bright early-type and very bright (Lx > 10d41) late-type galaxies. These discrepancies are likely caused by uncertainties in hot gas emission and SFHs, AGN contamination, and a lack of dynamically formed Low-mass XRBs. In our highest likelihood models, we find that hot gas emission dominates the emission for most bright galaxies. We also find that the evolution of the normal galaxy X-ray luminosity density out to z = 4 is driven largely by XRBs in galaxies with X-ray luminosities between 10d40 and 10d41 erg/s.

astro-ph.CO↗

arXiv2012

On the brightness distribution of Type Ia supernovae from violent white dwarf mergers

We investigate the brightness distribution expected for thermonuclear explosions that might result from the ignition of a detonation during the violent merger of white dwarf (WD) binaries. Determining their brightness distribution is critical for evaluating whether such an explosion model could be responsible for a significant fraction of the observed population of SNe Ia. We argue that the brightness of an explosion realized via the violent merger model is determined by the mass of nickel 56 produced in the detonation of the primary WD. We use a set of sub-Chandrasekhar mass WD detonation models to derive a relationship between primary WD mass and expected peak bolometric brightness. We use this relationship to convert the masses of merging primary WDs from binary population models to a predicted distribution of explosion brightness. We find a striking similarity between the shape of our theoretical peak-magnitude distribution and that observed for SNe Ia: our model produces a brightness distribution that roughly covers the range and matches the shape of the one observed for SNe Ia. However, this agreement hinges on a particular phase of mass accretion during binary evolution: the primary WD gains ~0.15-0.35 Msun from a slightly-evolved helium star companion. We also find that with high probability, violent WD mergers involving the most massive primaries (which should produce bright SNe) have delay times <500 Myr (Abridged).

astro-ph.SR↗

arXiv2012

The Population of Helium-Merger Progenitors: Observational Predictions

The helium-merger gamma-ray burst progenitor is produced by the rapid accretion onto a compact remnant (neutron star or black hole) when it undergoes a common envelope inspiral with its companion's helium core. This merger phase produces a very distinct environment around these outbursts and recent observations suggest that, in some cases, we are detecting the signatures of the past merger in the GRB afterglow. These observations allow us, for the first time, to study the specific features of the helium merger progenitor. In this paper, we couple population synthesis calculations to our current understanding of gamma-ray burst engines and common envelope evolution to make observational predictions for the helium-merger gamma-ray burst population. Many mergers do not produce GRB outbursts and we discuss the implications of these mergers with the broader population of astrophysical transients.

astro-ph.HE↗