arXiv subjects

Krzysztof Belczynski

Publications and source records attributed to Krzysztof Belczynski.

At least 73 records · Page 4Linked to original sources

arXiv2014

Black Hole X-ray Transients: The Formation Puzzle

There are 19 confirmed BH binaries in the Galaxy. 16 of them are X-ray transients hosting a ~5-15 Msun BH and a Roche-lobe overflowing low-mass companion. Companion masses are found mostly in 0.1-1 Msun mass range with peak at 0.6 Msun. The formation of these systems is believed to involve a common envelope phase, initiated by a BH progenitor, expected to be a massive star >20 Msun. It was realized that it may be very problematic for a low-mass companion to eject a massive envelope of the black hole progenitor. It invoked suggestions that an intermediate-mass companion ejects the envelope, and then is shredded by the Roche-lobe overflow to its current low-mass. But this creates another issue; a temperature mismatch between hot models and the observed cool low-mass donors. Finally, the main driver of Roche-lobe overflow that is believed to be magnetic braking does not seem to follow any theoretically calculated models. Number of ideas were put forward to explain various parts of this conundrum; pre-main sequence donor nature, alternative approach to magnetic braking and common envelope energy was revisited. We test various proposals and models to show that no overall solution exists so far. We argue that common envelope physics is not crucial in the understanding BH transient physical properties, but may affect significantly their formation rates. Our failure most likely indicates that either the current evolutionary models for low-mass stars and magnetic braking are not realistic or that the intrinsic population of BH transients is quite different from the observed one.

astro-ph.HE↗

arXiv2014

Stellar Mergers Are Common

The observed Galactic rate of stellar mergers or the initiation of common envelope phases brighter than M_V=-3 (M_I=-4) is of order 0.5 (0.3)/year with 90% confidence statistical uncertainties of 0.24-1.1 (0.14-0.65) and factor of 2 systematic uncertainties. The (peak) luminosity function is roughly dN/dL L^(-1.4+/-0.3), so the rates for events more luminous than V1309 Sco (M_V=-7 mag) or V838Mon (M_V=-10 mag) are lower at r~0.1/year and 0.03/year, respectively. The peak luminosity is a steep function of progenitor mass, L M^(2-3). This very roughly parallels the scaling of luminosity with mass on the main sequence, but the transients are ~2000-4000 times more luminous at peak. Combining these, the mass function of the progenitors, dN/dM M^(-2.0+/-0.8), is consistent with the initial mass function, albeit with broad uncertainties. These observational results are also broadly consistent with the estimates of binary population synthesis models. While extragalactic variability surveys can better define the rates and properties of the high luminosity events, systematic, moderate depth (I>16 mag) surveys of the Galactic plane are needed to characterize the low luminosity events. The existing Galactic samples are only ~20% complete and Galactic surveys are (at best) reaching a typical magnitude limit of <13 mag.

astro-ph.SR↗

arXiv2014

The effect of helium accretion efficiency on rates of Type Ia supernovae: double-detonations in accreting binaries

The double-detonation explosion scenario of Type Ia supernovae has gained increased support from the SN Ia community as a viable progenitor model, making it a promising candidate alongside the well-known single degenerate and double degenerate scenarios. We present delay times of double-detonation SNe, in which a sub-Chandrasekhar mass carbon-oxygen white dwarf accretes non-dynamically from a helium-rich companion. One of the main uncertainties in quantifying SN rates from double-detonations is the (assumed) retention efficiency of He-rich matter. Therefore, we implement a new prescription for the treatment of accretion/accumulation of He-rich matter on white dwarfs. In addition, we test how the results change depending on which criteria are assumed to lead to a detonation in the helium shell. In comparing the results to our standard case (Ruiter et al. 2011), we find that regardless of the adopted He accretion prescription, the SN rates are reduced by only 25% if low-mass He shells (< 0.05 Msun) are sufficient to trigger the detonations. If more massive (0.1 Msun) shells are needed, the rates decrease by 85% and the delay time distribution is significantly changed in the new accretion model - only SNe with prompt (< 500 Myr) delay times are produced. Since theoretical arguments favour low-mass He shells for normal double-detonation SNe, we conclude that the rates from double-detonations are likely to be high, and should not critically depend on the adopted prescription for accretion of He.

astro-ph.SR↗

arXiv2014

Comparison of LIGO/Virgo upper limits with predicted compact binary merger rates

We compare the current LIGO/Virgo upper limits on double compact object volumetric merger rates with our theoretical predictions. Our optimistic models are a factor of 3 below the existing upper limits for massive BH-BH systems with total mass 50-70 Msun, suggesting that a small increase in observational sensitivity may bring the first detections. The LIGO/Virgo gravitational wave observatories are currently being upgraded to advanced design sensitivity. If a sizeable population of BH-BH binaries is detected, the maximum total binary mass of this population will discriminate between two general families of common envelope models. If no binaries are detected, the new upper limits will provide astrophysically useful information about the environment and physical processes (e.g., metallicity of host galaxies or BH natal kicks) crucial to the formation of binaries containing black holes. For NS-NS systems, our predicted rates are 3 orders of magnitude below the current upper limits; even if advanced instruments reach their design sensitivities (factors of 10 times in distance, and 1,000 times in volumetric rate) the detection of NS-NS systems is not assured. However, we note that although our predicted NS-NS merger rates are consistent with estimates derived from Galactic NS-NS binaries and short GRBs, they are on the low side of these empirical estimates.

astro-ph.HE↗

arXiv2013

Double Compact Objects II: Cosmological Merger Rates

The development of advanced gravitational wave (GW) observatories, such as Advanced LIGO and Advanced Virgo, provides impetus to refine theoretical predictions for what these instruments might detect. In particular, with the range increasing by an order of magnitude, the search for GW sources is extending beyond the "local" Universe and out to cosmological distances. Double compact objects (neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS) and black hole-black hole (BH-BH) systems) are considered to be the most promising gravitational wave sources. In addition, NS-NS and/or BH-NS systems are thought to be the progenitors of gamma ray bursts (GRBs), and may also be associated with kilonovae. In this paper we present the merger event rates of these objects as a function of cosmological redshift. We provide the results for four cases, each one investigating a different important evolution parameter of binary stars. Each case is also presented for two metallicity evolution scenarios. We find that (i) in most cases NS-NS systems dominate the merger rates in the local Universe, while BH-BH mergers dominate at high redshift; (ii) BH-NS mergers are less frequent than other sources per unit volume, for all time; and (iii) natal kicks may alter the observable properties of populations in a significant way, allowing the underlying models of binary evolution and compact object formation to be easily distinguished. This is the second paper in a series of three. The third paper will focus on calculating the detection rates of mergers by gravitational wave telescopes.

astro-ph.HE↗

arXiv2012

X-ray Binary Evolution Across Cosmic Time

High redshift galaxies permit the study of the formation and evolution of X-ray binary populations on cosmological timescales, probing a wide range of metallicities and star-formation rates. In this paper, we present results from a large scale population synthesis study that models the X-ray binary populations from the first galaxies of the universe until today. We use as input to 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 and metallicity evolution of the universe. Our modeling, which is constrained by the observed X-ray properties of local galaxies, gives predictions about the global scaling of emission from X-ray binary populations with properties such as star-formation rate and stellar mass, and the evolution of these relations with redshift. Our simulations show that the X-ray luminosity density (X-ray luminosity per unit volume) from X-ray binaries in our Universe today is dominated by low-mass X-ray binaries, and it is only at z>2.5 that high-mass X-ray binaries become dominant. We also find that there is a delay of ~1.1 Gyr between the peak of X-ray emissivity from low-mass Xray binaries (at z~2.1) and the peak of star-formation rate density (at z~3.1). The peak of the X-ray luminosity from high-mass X-ray binaries (at z~3.9), happens ~0.8 Gyr before the peak of the star-formation rate density, which is due to the metallicity evolution of the Universe.

astro-ph.HE↗

arXiv2012

Cyg X-3: a low-mass black hole or a neutron star

Cyg X-3 is a highly interesting accreting X-ray binary, emitting from the radio to high-energy gamma-rays. It consists of a compact object wind-fed by a Wolf-Rayet (WR) star, but the masses of the components and the mass-loss rate have been a subject of controversies. Here, we determine its masses, inclination, and the mass-loss rate using our derived relationship between the mass-loss rate and the mass for WR stars of the WN type, published infrared and X-ray data, and a relation between the mass-loss rate and the binary period derivative (observed to be >0 in Cyg X-3). Our obtained mass-loss rate is almost identical to that from two independent estimates and consistent with other ones, which strongly supports the validity of this solution. The found WR and compact object masses are 10.3_{-2.8}^{+3.9}, 2.4_{-1.1}^{+2.1} solar masses, respectively. Thus, our solution still allows for the presence of either a neutron star or a black hole, but the latter only with a low mass. However, the radio, infrared and X-ray properties of the system suggest that the compact object is a black hole. Such a low-mass black-hole could be formed via accretion-induced collapse or directly from a supernova.

astro-ph.HE↗

arXiv2012

The X-ray Star Formation Story as Told by Lyman Break Galaxies in the 4 Ms CDF-S

We present results from deep X-ray stacking of >4000 high redshift galaxies from z~1 to 8 using the 4 Ms Chandra Deep Field South (CDF-S) data, the deepest X-ray survey of the extragalactic sky to date. The galaxy samples were selected using the Lyman break technique based primarily on recent HST ACS and WFC3 observations. Based on such high specific star formation rates (sSFRs): log SFR/M* > -8.7, we expect that the observed properties of these LBGs are dominated by young stellar populations. The X-ray emission in LBGs, eliminating individually detected X-ray sources (potential AGN), is expected to be powered by X-ray binaries and hot gas. We find, for the first time, evidence of evolution in the X-ray/SFR relation. Based on X-ray stacking analyses for z<4 LBGs (covering ~90% of the Universe's history), we find that the 2-10 keV X-ray luminosity evolves weakly with redshift (z) and SFR as log LX = 0.93 log (1+z) + 0.65 log SFR + 39.80. By comparing our observations with sophisticated X-ray binary population synthesis models, we interpret that the redshift evolution of LX/SFR is driven by metallicity evolution in HMXBs, likely the dominant population in these high sSFR galaxies. We also compare these models with our observations of X-ray luminosity density (total 2-10 keV luminosity per Mpc^3) and find excellent agreement. While there are no significant stacked detections at z>5, we use our upper limits from 5<z<8 LBGs to constrain the SMBH accretion history of the Universe around the epoch of reionization.

astro-ph.CO↗

arXiv2012

Cyg X-3: a Galactic double black hole or black hole-neutron star progenitor

There are no known double black hole (BH-BH) or black hole-neutron star (BH-NS) systems. We argue that Cyg X-3 is a very likely BH-BH or BH-NS progenitor. This Galactic X-ray binary consists of a compact object, wind-fed by a Wolf-Rayet (WR) type companion. Based on a comprehensive analysis of observational data, it was recently argued that Cyg X-3 harbors a 2-4.5 Msun BH and a 7.5-14.2 Msun WR companion. We find that the fate of such a binary leads to the prompt (<1 Myr) formation of a close BH-BH system for the high end of the allowed WR mass (M_WR>13 Msun). For the low- to mid-mass range of the WR star (M_WR=7-10 Msun) Cyg X-3 is most likely (probability 70%) disrupted when WR ends up as a supernova. However, with smaller probability, it may form a wide (15%) or a close (15%) BH-NS system. The advanced LIGO/VIRGO detection rate for mergers of BH-BH systems from the Cyg X-3 formation channel is 10 per year, while it drops down to 0.1 per year for BH-NS systems. If Cyg X-3 in fact hosts a low mass BH and massive WR star, it lends additional support for the existence of BH-BH/BH-NS systems.

astro-ph.HE↗

arXiv2012

Double Compact Objects I: The Significance Of The Common Envelope On Merger Rates

The last decade of observational and theoretical developments in stellar and binary evolution provides an opportunity to incorporate major improvements to the predictions from populations synthesis models. We compute the Galactic merger rates for NS-NS, BH-NS, and BH-BH mergers with the StarTrack code. The most important revisions include: updated wind mass loss rates (allowing for stellar mass black holes up to $80 \msun$), a realistic treatment of the common envelope phase (a process that can affect merger rates by 2--3 orders of magnitude), and a qualitatively new neutron star/black hole mass distribution (consistent with the observed "mass gap"). Our findings include: (i) The binding energy of the envelope plays a pivotal role in determining whether a binary merges within a Hubble time. (ii) Our description of natal kicks from supernovae plays an important role, especially for the formation of BH-BH systems. (iii) The masses of BH-BH systems can be substantially increased in the case of low metallicities or weak winds. (iv) Certain combinations of parameters underpredict the Galactic NS-NS merger rate, and can be ruled out. {\em (v)} Models incorporating delayed supernovae do not agree with the observed NS/BH "mass gap", in accordance with our previous work. This is the first in a series of three papers. The second paper will study the merger rates of double compact objects as a function of redshift, star formation rate, and metallicity. In the third paper we will present the detection rates for gravitational wave observatories, using up-to-date signal waveforms and sensitivity curves.

astro-ph.HE↗

arXiv2012

Common Proper Motion Wide White Dwarf Binaries Selected From The Sloan Digital Sky Survey

Wide binaries made up of two white dwarfs (WDs) receive far less attention than their tight counterparts. However, our tests using the binary population synthesis code {\tt StarTrack} indicate that, for any set of reasonable initial conditions, there exists a significant observable population of double white dwarfs (WDWDs) with orbital separations of 10$^2$ to 10$^5$ AU. We adapt the technique of Dhital et al.\ to search for candidate common proper motion WD companions separated by $<10\amin$ around the $>$12,000 spectroscopically confirmed hydrogen-atmosphere WDs recently identified in the Sloan Digital Sky Survey. Using two techniques to separate random alignments from high-confidence pairs, we find nine new high-probability wide WDWDs and confirm three previously identified candidate wide WDWDs. This brings the number of known wide WDWDs to 45; our new pairs are a significant addition to the sample, especially at small proper motions ($<$200 mas/yr) and large angular separations ($>$10\asec). Spectroscopic follow-up and an extension of this method to a larger, photometrically selected set of SDSS WDs may eventually produce a large enough dataset for WDWDs to realize their full potential as testbeds for theories of stellar evolution.

astro-ph.SR↗

arXiv2012

High Mass X-ray Binaries: Future Evolution and Fate

BH-NS and BH-BH systems are among the most promising gravitational wave sources detectable by advanced LIGO/VIRGO and the Einstein Telescope. Although the rates of these systems may be above those of NS-NS mergers, BH-NS and BH-BH systems are difficult to detect, and thusfar none have been observed. But the progenitors of BH-NS and BH-BH binary systems may have been observed, in the form of High-Mass X-ray Binaries (HMXBs). In this paper, we continue work studying these potential progenitors of these important gravitational wave sources. In the first two papers of the series, we have demonstrated that IC10 X-1 and NGC300 X-1 are direct progenitors of BH-BH systems and that Cyg X-1 may form, alas with a very low probability, a BH-NS system. Here, we analyze the Galactic binaries GX 301-2, Vela X-1, XTEJ1855-026, 4U1907+09, Cir X-1 and extra-galactic LMC X-1, LMC X-3, M33 X-1. In each case, we find that the future evolution will not allow the formation of a BH-NS nor a BH-BH system. Most of these binaries will soon merge in the common envelope phase, with a compact object sinking into a helium-rich core of a stellar companion. This "helium-merger" may be a progenitor for long duration gamma-ray bursts (GRBs). Based on the observed HMXB population, the rate of helium-mergers may make up a sizable fraction of long-duration GRBs. Due to this high number of potential GRB progenitors, a chance that a Galactic HMXB has caused one of the recent major mass extinction events is significant (10-20%).

astro-ph.HE↗

arXiv2011

On the apparent lack of be x-ray binaries with black holes in the galaxy and in the Magellanic clouds

In the Galaxy and in the Magellanic Clouds there are 170 Be X-ray binaries known to-date. Out of those, 111 host a neutron star, and for the reminder the nature of a companion is not known. None, so far, is known to host a black hole. This disparity is referred to as a missing Be -- black hole X-ray binary problem. The stellar population synthesis calculations following the formation of Be X-ray binaries in the Galaxy (Belczynski and Ziolkowski 2009) demonstrate that there is no problem of the missing Be+BH X-ray binaries for the Galaxy (the expected number of Be -- black hole X-ray binaries is 0 to 2, which is entirely consistent with the observed Galactic sample). However, the preliminary calculations for Magellanic Clouds indicate that there is a problem of the missing Be+BH X-ray binaries for the Clouds (the expected number is about 6, while none is observed). We believe, that to remove the discrepancy, one has to take into account a different history of the star formation rate in the Magellanic Clouds, with the respect to the Galaxy. New stellar population synthesis calculations are currently being carried out. An updated (as of November 2011) list of all 170 Be X-ray binaries known presently in the Galaxy and in the Magellanic Clouds is included.

astro-ph.SR↗

arXiv2011

The fate of Cyg X-1: an empirical lower limit on BH-NS merger rate

The recent distance determination allowed precise estimation of the orbital parameters of Cyg X-1, which contains a massive 14.8 Msun BH with a 19.2 Msun O star companion. This system appears to be the clearest example of a potential progenitor of a BH-NS system. We follow the future evolution of Cyg X-1, and show that it will soon encounter a Roche lobe overflow episode, followed shortly by a Type Ib/c supernova and the formation of a NS. It is demonstrated that in majority of cases (70%) the supernova and associated natal kick disrupts the binary due to the fact that the orbit expanded significantly in the Roche lobe overflow episode. In the reminder of cases (30%) the newly formed BH-NS system is too wide to coalesce in the Hubble time. Only sporadically (1%) a Cyg X-1 like binary may form a coalescing BH-NS system given a favorable direction and magnitude of the natal kick. If Cyg X-1 like channel (comparable mass BH-O star bright X-ray binary) is the only or dominant way to form BH-NS binaries in the Galaxy we can estimate the empirical BH-NS merger rate in the Galaxy at the level of 0.001 per Myr. This rate is so low that the detection of BH-NS systems in gravitational radiation is highly unlikely, generating Advanced LIGO/VIRGO detection rates at the level of only 1 per century. If BH-NS inspirals are in fact detected, it will indicate that the formation of these systems proceeds via some alternative and yet unobserved channels.

astro-ph.GA↗

arXiv2011

The coalescence rates of double black holes

We present the summary of the recent investigations of double black hole binaries in context of their formation and merger rates. In particular we discuss the spectrum of black hole masses, the formation scenarios in the local Universe and the estimates of detection rates for gravitational radiation detectors like LIGO and VIRGO. Our study is based on observed properties of known Galactic and extra-galactic stellar mass black holes and evolutionary predictions. We argue that the binary black holes are the most promising source of gravitational radiation.

astro-ph.HE↗

arXiv2010

IC10~X-1/NGC300~X-1: the very immediate progenitors of BH-BH binaries

We investigate the future evolution of two extragalactic X-ray binaries: IC10 X-1 and NGC300 X-1. Each of them consists of a high mass BH ($\sim 20-30 \msun$) accreting from a massive WR star companion ($\gtrsim 20 \msun$), and both are located in low metallicity galaxies. We analyze the current state of the systems and demonstrate that both systems will very quickly ($\lesssim 0.3$ Myr) form close BH-BH binaries with the short coalescence time ($\sim 3$ Gyr) and large chirp mass ($\sim 15 \msun$). The formation of BH-BH system seems unavoidable, as {\em (i)} WR companions are well within their Roche lobes and they do not expand so no Roche lobe overflow is expected, {\em (ii)} even intense WR wind mass loss does not remove sufficient mass to prohibit the formation of the second BH, {\em (ii)} even if BH receives the large natal kick, the systems are very closely bound and are almost impossible to disrupt. As there are two such immediate BH-BH progenitor systems within 2 Mpc and as the current gravitational wave instruments LIGO/VIRGO (initial stage) can detect such massive BH-BH mergers out to $\sim 200$ Mpc, the empirically estimated detection rate of such inspirals is $R=3.36^{+8.29}_{-2.92}$ at the 99% confidence level. If there is no detection in the current LIGO/VIRGO data (unreleased year of $s6$ run), the existence of these two massive BH systems poses an interesting challenge. Either the gravitational radiation search is not sensitive to massive inspirals or there is some fundamental misunderstanding of stellar evolution physics leading directly to the formation of BH-BH binaries.

astro-ph↗

arXiv2010

Double Compact Objects as Low-frequency Gravitational Wave Sources

We study the Galactic field population of double compact objects (NS-NS, BH-NS, BH-BH binaries) to investigate the number (if any) of these systems that can potentially be detected with LISA at low gravitational-wave frequencies. We calculate the Galactic numbers and physical properties of these binaries and show their relative contribution from the disk, bulge and halo. Although the Galaxy hosts 10^5 double compact object binaries emitting low-frequency gravitational waves, only a handful of these objects in the disk will be detectable with LISA, but none from the halo or bulge. This is because the bulk of these binaries are NS-NS systems with high eccentricities and long orbital periods (weeks/months) causing inefficient signal accumulation (small number of signal bursts at periastron passage in 1 yr of LISA observations) rendering them undetectable in the majority of these cases. We adopt two evolutionary models that differ in their treatment of the common envelope phase that is a major (and still mostly unknown) process in the formation of close double compact objects. Depending on the adopted evolutionary model, our calculations indicate the likely detection of about 4 NS-NS binaries and 2 BH-BH systems (model A; likely survival of progenitors through CE) or only a couple of NS-NS binaries (model B; suppression of the double compact object formation due to CE mergers).

astro-ph↗

arXiv2010

Spectra of Type Ia Supernovae from Double Degenerate Mergers

The merger of two white dwarfs (a.k.a. double degenerate merger) has often been cited as a potential progenitor of type Ia supernovae. Here we combine population synthesis, merger and explosion models with radiation-hydrodynamics light-curve models to study the implications of such a progenitor scenario on the observed type Ia supernova population. Our standard model, assuming double degenerate mergers do produce thermonuclear explosions, produces supernova light-curves that are broader than the observed type Ia sample. In addition, we discuss how the shock breakout and spectral features of these double degenerate progenitors will differ from the canonical bare Chandrasekhar-massed explosion models. We conclude with a discussion of how one might reconcile these differences with current observations.

astro-ph.SR↗