Constraining Binary Evolution with Gravitational Wave Measurements of Chirp Masses

Using the StarTrack binary population synthesis code we investigate the properties of population of compact object binaries. Taking into account the selection effects we calculate the expected properties of the observed binaries.We analyze possible constraints on the stellar evolution models and find that an observed sample of about one hundred mergers will yield strong constraints on the binary evolution scenarios.Comment: Invited talk at "The Astrophysics of Gravitational Wave Sources" Workshop; April 24-26, 2003, U. Maryland; 10 page

The distribution of mass ratios in compact object binaries

Using the StarTrack population synthesis code we compute the distribution of masses of merging compact object (black hole or neutron star) binaries. The shape of the mass distribution is sensitive to some of the parameters governing the stellar binary evolution. We discuss the possibility of constraining stellar evolution models using mass measurements obtained from the detection of compact object inspiral with the upcoming gravitational-wave observatories.Comment: 10 pages, uses spie.cls, Proc of the SPIE Conference "Astronomical Telescopes and Instrumentation

Gravitational lensing as a probe of compact object population in the Galaxy

The population of solitary compact objects in the Galaxy is very diffcult to investigate. In this paper we analyze the possibility of using microlensing searches to detect and to analyze the properties of the solitary black holes and neutron stars. Evolution of single and binary stars is considered using the StarTrack population synthesis code. We investigate the properties of the Galactic population of compact objects numerically. We find that the compact object lensing events are concentrated in a region with the radius of $\approx 5$ degrees around the Galactic center. The distribution of masses of the lenses for the models we consider differs but only slightly from the underlying massdistribution. The expected detection rates are of the order of a few per year.Comment: Submitted to Astronomy and Astrophysic

Synthetic catalog of black holes in the Milky Way

We present an open-access database which includes a synthetic catalog of black holes in the Milky Way. To calculate evolution of single and binary stars we used updated population synthesis code StarTrack. We applied a new model of star formation history and chemical evolution of Galactic disk, bulge and halo synthesized from observational and theoretical data. We find that at the current moment Milky Way (disk+bulge+halo) contains about 1.2 x 10^8 single black holes with average mass of about 14 Msun and 9.3 x 10^6 BHs in binary systems with average mass of 19 Msun. We present basic statistical properties of BH populations such as distributions of single and binary BH masses, velocities, orbital parameters or numbers of BH binary systems in different evolutionary configurations. We find that the most massive BHs are formed in mergers of binary systems, such as BH-MS, BH+He, BH-BH. The metallicity of stellar population has a significant impact on the final BH mass due to the stellar winds. Therefore the most massive single BH in our simulation, 113 Msun, originates from a merger of a helium star and a black hole in a low metallicity stellar environment in Galactic halo. The most massive BH in binary system is 60 Msun and was also formed in Galactic halo. We constrain that only 0.006% of total Galactic halo mass (including dark matter) could be hidden in the form of stellar origin BHs which are not detectable by current observational surveys. Galactic binary BHs are minority (10% of all Galactic BHs) and most of them are in BH-BH systems. The current Galactic merger rates for two considered common envelope models which are: 3-81 Myr^-1 for BH-BH, 1-9 Myr^-1, for BH-NS and 14-59 Myr^-1 for NS-NS systems. Data files are available at https://bhc.syntheticuniverse.org/.Comment: 21 pages, A&A accepted, data from catalog available onlin

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.Comment: 9 pages, 5 figures, accepted to A&

Black hole - neutron star mergers: the first mass gap and kilonovae

Observations of X-ray binaries indicate a dearth of compact objects in the mass range from $\sim 2-5$ $M_{\odot}$ and the existence of this (first mass) gap has been used to advance our understanding of the engines behind core-collapse supernovae. LIGO/Virgo observations provide an independent measure of binary compact remnant masses and several candidate first mass gap objects (either NS or BH) were observed in the O3 science run. We study the formation of BH-NS mergers in the framework of isolated classical binary evolution. We use population synthesis method to evolve binary stars (Population I and II) across cosmic time. The predicted BH-NS mergers from the isolated classical binary evolution are sufficiently abundant ($\sim 0.4-10$ $Gpc^{-3} yr^{-1}$) in the local Universe ($z\approx0$) to produce the observed LIGO/Virgo candidates. We present results on the NS to BH mass ratios ($q=M_{\rm NS}/M_{\rm BH}$ ) in merging systems, showing that although systems with a mass ratio as low as $q=0.02$ can exist, only a small fraction ($\sim 0.05\%-5\%$) of LIGO/Virgo detectable BH-NS mergers have mass ratios below $q=0.05$. We find that with appropriate constraints on the (delayed) supernova engine $\sim 30-40\%$ of LIGO/Virgo BH-NS mergers may host at least one compact object in the gap. The uncertainties in the processes behind compact object formation imply that the fraction of BH-NS systems ejecting mass during the merger is $\sim 0-9\%$. In our reference we find that only $\sim 0.2\%$ of BH-NS mergers will have any mass ejection, and about the same percentage would produce kilonova bright enough to have a chance to be detected even with a large (Subaru-class) $8$m telescope. Interestingly, all these mergers will have both BH and NS in the first mass gap.Comment: 14 pages, 12 figure