Binary neutron star mergers (BNSMs) is currently the most promising source of \textsl{r}-process thanks to the detection of GW170817. The estimated occurring frequency and the amount of mass ejected per merger indicate that BNSMs by itself can account for all the \textsl{r}-process enrichment in the Galaxy. However, the decreasing trend of [Eu/Fe] vs [Fe/H] of disk stars for [Fe/H]$\gtrsim -1$ in the solar neighborhood is inconsistent with the flat trend expected from BNSMs with a standard delay time distribution (DTD) $\propto t^{-1}$. This has led to the suggestion that either additional sources or modification to the DTD of BNSMs is required to match the observations. We investigate the effects of natal kicks received during the birth of neutron star binaries on the chemical evolution of \textsl{r}-process element Eu in the Milky Way by combining the results from the galactic dynamics code \textsc{galpy} with a one-zone Galactic chemical evolution model \textsc{omega}. We show that when key inputs from simulations of the inside-out disk evolution are combined with natal kicks, BNSMs can naturally reproduce the observed decreasing trend of [Eu/Fe] with [Fe/H] in the solar neighborhood without the need for modification to the DTD or additional \textsl{r}-process sources.
We study the impact of the neutron star binaries' (NSBs) natal kick distribution on the Galactic r-process enrichment. We model the growth of a Milky Way type halo based on N-body simulation results and its star formation history based on multi epoch abundance matching techniques. We consider the NSBs that merge well beyond the galaxy's effective radius ($>2\times R_\mathrm{eff}$) do not contribute to Galactic r-process enrichment. Assuming a power-law delay-time distribution (DTD) function ($\propto t^{-1}$) with $t_\mathrm{min}=30$ Myr for binaries' coalescence timescales, and an exponential…
The birth kicks of black holes, arising from asymmetric mass ejection or neutrino emission during core-collapse supernovae, are of great interest for both observationally constraining supernova models and population-synthesis studies of binary evolution. Recently, several efforts were undertaken to estimate black hole birth kicks from observations of black-hole low-mass X-ray binaries. We follow up on this work, specifically focussing on the highest estimated black-hole kick velocities. We find that existing observations do not require black hole birth kicks in excess of approximately 100 km/s…
Based on recent results from three-dimensional supernova simulations and semi-analytical parametrised models, we develop analytical prescriptions for the dependence of the mass of neutron stars and black holes and the natal kicks, if any, on the pre-supernova carbon-oxygen core and helium shell masses. Our recipes are probabilistic rather than deterministic in order to account for the intrinsic stochasticity of stellar evolution and supernovae. We anticipate that these recipes will be particularly useful for rapid population synthesis, and we illustrate their application to distributions of re…
The long wait for the detection of merging black hole -- neutron star (BH--NS) binaries is finally over with the announcement by the LIGO/Virgo/Kagra collaboration of GW200105 and GW200115. Remarkably, the primary of GW200115 has a negative spin projection onto the orbital angular momentum, with about $90\%$ probability. Merging BH--NS binaries are expected to form mainly through the evolution of massive binary stars in the field, since their dynamical formation in dense star clusters is strongly suppressed by mass segregation. In this paper, we carry out a systematic statistical study of the …
We study galactic enrichment with rapid neutron capture (r-process) elements in cosmological, magnetohydrodynamical simulations of a Milky Way-mass galaxy. We include a variety of enrichment models, based on either neutron star mergers or a rare class of core-collapse supernova as sole r-process sources. For the first time in cosmological simulations, we implement neutron star natal kicks on-the-fly to study their impact. With kicks, neutron star mergers are more likely to occur outside the galaxy disc, but how far the binaries travel before merging also depends on the kick velocity distributi…
We investigate whether stellar-mass black holes have to receive natal kicks in order to explain the observed distribution of low-mass X-ray binaries containing black holes within our Galaxy. Such binaries are the product of binary evolution, where the massive primary has exploded forming a stellar-mass black hole, probably after a common envelope phase where the system contracted down to separations of order 10-30 Rsun. We perform population synthesis calculations of these binaries, applying both kicks due to supernova mass-loss and natal kicks to the newly-formed black hole. We then integrate…
We investigate the dynamical evolution of a star cluster in an external tidal field by using N-body simulations, with focus on the effects of the presence or absence of neutron star natal velocity kicks.We show that, even if neutron stars typically represent less than 2% of the total bound mass of a star cluster, their primordial kinematic properties may affect the lifetime of the system by up to almost a factor of four. We interpret this result in the light of two known modes of star cluster dissolution, dominated by either early stellar evolution mass loss or two-body relaxation. The competi…
The masses of stellar-remnant black holes (BH), as a result of their formation via massive single- and binary-stellar evolution, is of high interest in this era of gravitational-wave detection from binary black hole (BBH) and binary neutron star (BNS) mergers. Here we present new developments in the N-body evolution program NBODY7 in regards to its stellar-remnant formation and related schemes. We demonstrate that the newly-implemented stellar-wind and remnant-formation schemes in the NBODY7 code's BSE sector, such as the 'rapid' and the 'delayed' supernova (SN) schemes along with an implement…
White Dwarf Natal Kicks as Velocity-Space Random Walks. II. Binary Stellar Evolution and Observational Kick Constraints
University of Colorado（科罗拉多大学）；National Institute of Standards and Technology（美国国家标准与技术研究院）；Université Côte d’Azur（蔚蓝海岸大学）；Observatoire de la Côte d’Azur（蔚蓝海岸天文台）
The role of accretion efficiency, natal kicks, and angular momentum transport in the formation of the Gaia black holes
Universität Heidelberg（海德堡大学）；University of Padova（帕多瓦大学）；INAF - Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Universitat de Barcelona（巴塞罗那大学）
White Dwarf Natal Kicks as Velocity-Space Random Walks. I. Fokker-Planck Theory
JILA, University of Colorado and National Institute of Standards and Technology（科罗拉多大学与美国国家标准技术研究院联合JILA实验室）；Department of Astrophysical and Planetary Sciences, University of Colorado（科罗拉多大学天体物理与行星科学系）；Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Lagrange（蔚蓝海岸大学、蔚蓝海岸天文台、法国国家科学研究中心拉格朗日实验室）
Stars passing too close to a black hole can produce tidal disruption events (TDEs), when the tidal force across the star exceeds the gravitational force that binds it. TDEs have usually been discussed in relation to massive black holes that reside in the centres of galaxies or lurk in star clusters. In this paper, we investigate the possibility that triple stars hosting a stellar black hole (SBH) may be sources of TDEs. We start from a triple system made up of three main sequence (MS) stars and model the supernova (SN) kick event that led to the production of an inner binary comprised of a SBH…
Using a Monte Carlo code, we construct a dynamic evolutionary model of the Galactic globular cluster M22 (NGC6656). The initial conditions are chosen so that, after about 12Gyr of stellar and dynamical evolution, the model is an approximate fit to the surface brightness and velocity dispersion profiles of the cluster, to its mass function, and to the current binary fraction. Depending on the distribution of black hole natal kicks, we predict that the present-day population of stellar-mass black holes ranges from about 40 (no kicks) down to essentially zero (kicks distributed like those of neut…
The current interpretation of LIGO--Virgo--KAGRA data suggests that the primary mass function of merging binary black holes (BBHs) at redshift $z\lesssim 1$ contains multiple structures, while spins are relatively low. Theoretical models of BBH formation in different environments can provide a key to interpreting the population of observed mergers, but they require the simultaneous treatment of stellar evolution and dynamics, galaxy evolution, and general relativity. We present \texttt{B-POP}, a population synthesis tool to model BBH mergers formed in the field or via dynamical interactions in…
California Institute of Technology（加州理工学院）；University of California, Los Angeles（加州大学洛杉矶分校）；Mani L. Bhaumik Institute for Theoretical Physics（马尼·L·巴乌米克理论物理研究所）
Mergers of black hole (BH) and neutron star (NS) binaries are expected to be observed by gravitational wave observatories in the coming years. Until now, LIGO has only set an upper limit on this merger rate. BH-NS binaries are expected to merge in isolation, as their formation is suppressed in star clusters by the mass segregation and the strong heating by BHs in the cluster core. Another viable scenario to BH-NS mergers is in triple systems. In this paper, we carry out a systematic statistical study of the dynamical evolution of triples comprised of an inner BH-NS binary by means of high-prec…
We investigate the statistics of isolated recycled pulsars and double neutron star binaries in the Galactic disk. Since recycled pulsars are believed to form through accretion and spinup in close binaries, the isolated objects presumably originate from disrupted progenitors of double neutron stars. There are a comparable number of double neutron star systems compared to isolated recycled pulsars. We find that standard evolutionary models cannot explain this fact, predicting several times the number of isolated recycled pulsars than those in double neutron star systems. We demonstrate, through …
We evaluate the redshift distribution of binary black hole (BBH), black hole - neutron star binary (BHNS) and binary neutron star (BNS) mergers, exploring the main sources of uncertainty: star formation rate (SFR) density, metallicity evolution, common envelope, mass transfer via Roche lobe overflow, natal kicks, core-collapse supernova model and initial mass function. Among binary evolution processes, uncertainties on common envelope ejection have a major impact: the local merger rate density of BNSs varies from $\sim{}10^3$ to $\sim{}20$ Gpc$^{-3}$ yr$^{-1}$ if we change the common envelope …
We consider how dynamical friction acts on black holes that receive a velocity kick while located at the center of a gravitational potential, analogous to a star cluster, due to either a natal kick or the anisotropic emission of gravitational waves during a black hole-black hole merger. Our investigation specifically focuses on how well various Chandrasekhar-based dynamical friction models can predict the orbital decay of kicked black holes with $m_{bh} \lesssim 100 M_\odot$ due to an inhomogeneous background stellar field. In general, the orbital evolution of a kicked black hole follows that …
The recent aLIGO/aVirgo discovery of gravitational waves from the neutron star merger (NSM) GW170817 and the follow up kilonova observations have shown that NSMs produce copious amount of r-process material. However, it is difficult to reconcile the large natal kicks and long average merging times of Double Neutron Stars (DNSs), with the levels of r-process enrichment seen in ultra faint dwarf (UFD) galaxies such as Reticulum II and Tucana III. Assuming that such dwarf systems have lost a significant fraction of their stellar mass through tidal stripping, we conclude that contrary to most curr…
The cosmic merger rate density of black hole binaries (BHBs) can give us an essential clue to constraining the formation channels of BHBs, in light of current and forthcoming gravitational wave detections. Following a Monte Carlo approach, we couple new population-synthesis models of BHBs with the Illustris cosmological simulation, to study the cosmic history of BHB mergers. We explore six population-synthesis models, varying the prescriptions for supernovae, common envelope, and natal kicks. In most considered models, the cosmic BHB merger rate follows the same trend as the cosmic star format…
About ten to 20 percent of massive stars may be kicked out of their natal clusters before exploding as supernovae. These "runaway stars" might play a crucial role in driving galactic outflows and enriching the circumgalactic medium with metals. To study this effect, we carry out high resolution dwarf galaxy simulations that include velocity kicks to massive O/B stars above 8 M$_{\odot}$. We consider two scenarios, one that adopts a power law velocity distribution for kick velocities, resulting in more stars with high velocity kicks, and a more moderate scenario with a Maxwellian velocity distr…
Wide black hole binaries (wide-BBHs; $\geqslant 10^3$ AU) in the field can be perturbed by random stellar flybys that excite their eccentricities. Once a wide binary is driven to a sufficiently small pericenter approach, gravitational wave (GW) emission becomes significant, and the binary inspirals and merges. In our previous study, using simplified models for wide-BBHs, we found that successive flybys lead to significant merger fractions of wide-BBHs in less than Hubble time, making the flyby perturbation mechanism a relevant contributor to the production rate of GW-sources. However, the exac…
We explore the possibility of inferring the properties of the Galactic neutron star population through machine learning. In particular, in this paper we focus on their dynamical characteristics and show that an artificial neural network is able to estimate with high accuracy the parameters which control the current positions of a mock population of pulsars. For this purpose, we implement a simplified population-synthesis framework (where selection biases are neglected at this stage) and concentrate on the natal kick-velocity distribution and the distribution of birth distances from the Galacti…
We study the enrichment and mixing of r-process elements in ultrafaint dwarf galaxies (UFDs). We assume that r-process elements are produced by neutron-star mergers (NSMs), and examine multiple models with different natal kick velocities and explosion energies. To this end, we perform cosmological simulations of galaxy formation to follow mixing of the dispersed r-process elements driven by star formation and the associated stellar feedback in progenitors of UFDs. We show that the observed europium abundance in Reticulum II is reproduced by our inner explosion model where a NSM is triggered at…
Double Neutron Star Delay Times Across Cosmic Metallicities: The Role of Helium Star Progenitors
University of Florida（佛罗里达大学）；Institute for Fundamental Theory（基础理论研究所）；Université de Genève（日内瓦大学）；Gravitational Wave Science Center (GWSC)（引力波科学中心）；Northwestern University（西北大学）；Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA)（天体物理学跨学科探索与研究中心）
Astrometric microlensing probes of the isolated neutron star population with Roman
Zentrum für Astronomie der Universität Heidelberg（海德堡大学天文中心）；Space Science Institute, Lawrence Livermore National Laboratory（空间科学研究所，劳伦斯利弗莫尔国家实验室）；Georgia Institute of Technology（佐治亚理工学院）
Six gravitational wave detections have been reported so far, providing crucial insights on the merger rate of double compact objects. We investigate the cosmic merger rate of double neutron stars (DNSs), neutron star-black hole binaries (NSBHs) and black hole binaries (BHBs) by means of population-synthesis simulations coupled with the Illustris cosmological simulation. We have performed six different simulations, considering different assumptions for the efficiency of common envelope (CE) ejection and exploring two distributions for the supernova (SN) kicks. The current BHB merger rate derive…
We chart the expected Galactic distribution of neutron stars and black holes. These compact remnants of dead stars -- the Galactic underworld -- are found to exhibit a fundamentally different distribution and structure to the visible Galaxy. Compared to the visible Galaxy, concentration into a thin flattened disk structure is much less evident with the scale height more than tripling to 1260 +- 30 pc. This difference arises from two primary causes. Firstly, the distribution is in part inherited from the integration over the evolving structure of the Galaxy itself (and hence the changing distri…
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 signi…
Fast Dynamical Modelling of Milky Way Globular Clusters -- II. Impacts of Black Hole Prescriptions
Saint Mary’s University（圣玛丽大学）；Universitat de Barcelona (UB)（巴塞罗那大学）；ICREA（加泰罗尼亚高级研究院）；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究所）；Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik（海德堡大学天文学中心理论天体物理研究所）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；Department of Physics and Astronomy, University of Heidelberg（海德堡大学物理与天文系）
