We explore a newly proposed channel to create binary black holes of stellar origin. This scenario applies to massive, tight binaries where mixing induced by rotation and tides transports the products ...of hydrogen burning throughout the stellar envelopes. This slowly enriches the entire star with helium, preventing the build-up of an internal chemical gradient. The stars remain compact as they evolve nearly chemically homogeneously, eventually forming two black holes, which we estimate typically merge 4–11 Gyr after formation. Like other proposed channels, this evolutionary pathway suffers from significant theoretical uncertainties, but could be constrained in the near future by data from advanced ground-based gravitational-wave detectors. We perform Monte Carlo simulations of the expected merger rate over cosmic time to explore the implications and uncertainties. Our default model for this channel yields a local binary black hole merger rate of about 10 Gpc−3 yr−1 at redshift z = 0, peaking at twice this rate at z = 0.5. This means that this channel is competitive, in terms of expected rates, with the conventional formation scenarios that involve a common-envelope phase during isolated binary evolution or dynamical interaction in a dense cluster. The events from this channel may be distinguished by the preference for nearly equal-mass components and high masses, with typical total masses between 50 and 110 M⊙. Unlike the conventional isolated binary evolution scenario that involves shrinkage of the orbit during a common-envelope phase, short time delays are unlikely for this channel, implying that we do not expect mergers at high redshift.
Pair-instability and pulsational pair-instability supernovae (PPISNe) have not been unambiguously observed so far. They are, however, promising candidates for the progenitors of the heaviest binary ...black hole (BBH) mergers detected. If these BBHs are the product of binary evolution, then PPISNe could occur in very close binaries. Motivated by this, we discuss the implications of a PPISN happening with a close binary companion and what impact these events have on the formation of merging BBHs through binary evolution. For this, we have computed a set of models of metal-poor (Z /10) single helium stars using the MESA software instrument. For PPISN progenitors with pre-pulse masses >50 M we find that, after a pulse, heat deposited throughout the layers of the star that remain bound causes it to expand to more than 100 R for periods of 102-104 yr depending on the mass of the progenitor. This results in long-lived phases of Roche lobe overflow or even common-envelope events if there is a close binary companion, leading to additional electromagnetic transients associated with PPISN eruptions. If we ignore the effect of these interactions, we find that mass loss from PPISNe reduces the final BH spin by ∼30%, induces eccentricities below the threshold of detectability of the LISA observatory, and can produce a double-peaked distribution of measured chirp masses in BBH mergers observed by ground-based detectors.
ABSTRACT
We investigate the impact of uncertainty in the metallicity-specific star formation rate over cosmic time on predictions of the rates and masses of double compact object mergers observable ...through gravitational waves. We find that this uncertainty can change the predicted detectable merger rate by more than an order of magnitude, comparable to contributions from uncertain physical assumptions regarding binary evolution, such as mass transfer efficiency or supernova kicks. We statistically compare the results produced by the COMPAS population synthesis suite against a catalogue of gravitational-wave detections from the first two Advanced LIGO and Virgo observing runs. We find that the rate and chirp mass of observed binary black hole mergers can be well matched under our default evolutionary model with a star formation metallicity spread of 0.39 dex around a mean metallicity 〈Z〉 that scales with redshift z as 〈Z〉 = 0.035 × 10−0.23z, assuming a star formation rate of $0.01 \times (1+z)^{2.77} / (1+((1+z)/2.9)^{4.7}) \, \rm {M}_\odot$ Mpc−3 yr−1. Intriguingly, this default model predicts that 80 per cent of the approximately one binary black hole merger per day that will be detectable at design sensitivity will have formed through isolated binary evolution with only dynamically stable mass transfer, i.e. without experiencing a common-envelope event.
We present HST/WFC3 ultraviolet imaging in the F275W and F336W bands of the Type IIb SN 2001ig at an age of more than 14 years. A clear point source is detected at the site of the explosion, with ...mF275W = 25.39 0.10 and mF336W = 25.88 0.13 mag. Despite weak constraints on both the distance to the host galaxy NGC 7424 and the line-of-sight reddening to the supernova, this source matches the characteristics of an early B-type main-sequence star with 19,000 < Teff < 22,000 K and . A BPASS v2.1 binary evolution model, with primary and secondary masses of 13 M and 9 M , respectively, is found to simultaneously resemble, in the Hertzsprung-Russell diagram, both the observed location of this surviving companion, and the primary star evolutionary endpoints for other Type IIb supernovae. This same model exhibits highly variable late-stage mass loss, as expected from the behavior of the radio light curves. A Gemini/GMOS optical spectrum at an age of 6 years reveals a narrow He ii λ4686 emission line, indicative of continuing interaction with a dense circumstellar medium at large radii from the progenitor. We review our findings on SN 2001ig in the context of binary evolution channels for stripped-envelope supernovae. Owing to the uncrowded nature of its environment in the ultraviolet, this study of SN 2001ig represents one of the cleanest detections to date of a surviving binary companion to a Type IIb supernova.
During its first four months of taking data, Advanced LIGO has detected gravitational waves from two binary black hole mergers, GW150914 and GW151226, along with the statistically less significant ...binary black hole merger candidate LVT151012. Here we use the rapid binary population synthesis code COMPAS to show that all three events can be explained by a single evolutionary channel-classical isolated binary evolution via mass transfer including a common envelope phase. We show all three events could have formed in low-metallicity environments (Z=0.001) from progenitor binaries with typical total masses ≳160M
, ≳60M
and ≳90M
, for GW150914, GW151226 and LVT151012, respectively.
ABSTRACT
Mergers of black hole–neutron star (BHNS) binaries have now been observed by gravitational wave (GW) detectors with the recent announcement of GW200105 and GW200115. Such observations not ...only provide confirmation that these systems exist but will also give unique insights into the death of massive stars, the evolution of binary systems and their possible association with gamma-ray bursts, r-process enrichment, and kilonovae. Here, we perform binary population synthesis of isolated BHNS systems in order to present their merger rate and characteristics for ground-based GW observatories. We present the results for 420 different model permutations that explore key uncertainties in our assumptions about massive binary star evolution (e.g. mass transfer, common-envelope evolution, supernovae), and the metallicity-specific star formation rate density, and characterize their relative impacts on our predictions. We find intrinsic local BHNS merger rates spanning $\mathcal {R}_{\rm {m}}^0 \approx$ 4–830 $\, \rm {Gpc}^{-3}$$\, \rm {yr}^{-1}$ for our full range of assumptions. This encompasses the rate inferred from recent BHNS GW detections and would yield detection rates of $\mathcal {R}_{\rm {det}} \approx 1$–180$\, \rm {yr}^{-1}$ for a GW network consisting of LIGO, Virgo, and KAGRA at design sensitivity. We find that the binary evolution and metallicity-specific star formation rate density each impacts the predicted merger rates by order $\mathcal {O}(10)$. We also present predictions for the GW-detected BHNS merger properties and find that all 420 model variations predict that $\lesssim 5{{\ \rm per\ cent}}$ of the BHNS mergers have BH masses $m_{\rm {BH}} \gtrsim 18\, \rm {M}_{\odot }$, total masses $m_{\rm {tot}} \gtrsim 20\, \rm {M}_{\odot }$, chirp masses ${\mathcal {M}}_{\rm {c}} \gtrsim 5.5\, \rm {M}_{\odot }$, and mass ratios qf ≳ 12 or qf ≲ 2. Moreover, we find that massive NSs with $m_{\rm {NS}} \gt 2\, \rm {M}_{\odot }$ are expected to be commonly detected in BHNS mergers in almost all our model variations. Finally, a wide range of $\sim 0{{\ \rm per\ cent}}$ to $70{{\ \rm per\ cent}}$ of the BHNS mergers are predicted to eject mass during the merger. Our results highlight the importance of considering variations in binary evolution and cosmological models when predicting, and eventually evaluating, populations of BHNS mergers.
Abstract State-of-the-art surveys reveal that most massive stars in the Universe evolve in close binaries. Massive stars in such systems are expected to develop aspherical envelopes due to tidal ...interactions and/or rotational effects. Recently, it was shown that point explosions in oblate stars can produce relativistic equatorial ring-like outflows. Moreover, since stripped-envelope stars in binaries can expand enough to fill their Roche lobes anew, it is likely that these stars die with a greater degree of asphericity than the oblate spheroid geometry previously studied. We investigate the effects of this asymmetry by studying the gas dynamics of axisymmetric point explosions in stars in various stages of filling their Roche lobes. We find that point explosions in these pear-shaped stars produce transrelativistic ejecta that coalesce into bullets pointed both toward and away from the binary companion. We present this result and comment on key morphological differences between core-collapse explosions in spherical versus distorted stars in binary systems, effects on gravitational wave sources, and observational signatures that could be used to glean these explosion geometries from current and future surveys.
Abstract
Type Ia supernovae (SNe Ia) are thought to be the result of thermonuclear explosions in white dwarfs (WDs). Commonly considered formation pathways include two merging WDs (the ...double-degenerate channel) and a single WD accreting material from a H or He donor (the single-degenerate channel). Since the predicted SN Ia rates from WDs in binaries are thought to be insufficient to explain the observed SN Ia rate, it is important to study similar interactions in higher-order multiple-star systems such as triple systems. We use the evolutionary population synthesis code Multiple Stellar Evolution (MSE) to study the stellar evolution, binary interactions, and gravitational dynamics of the triple-star systems. Also, unlike previous studies, prescriptions are included to simultaneously take into account the single- and double-degenerate channels, and we consider triples across the entire parameter space (including those with tight inner binaries). We explore the impact of typically ignored or uncertain physics such as flybys and common envelope prescription parameters on our results. The majority of systems undergo circular mergers to explode as SNe Ia, while eccentric collisions contribute to 0.4%−4% of SN Ia events. The time-integrated SN Ia rate from the triple channel is found to be
(
3.60
±
0.04
)
×
10
−
4
M
⊙
−
1
, which is, surprisingly, similar to that of the isolated binary channel, where the SN Ia rate is
(
3.2
±
0.1
)
×
10
−
4
M
⊙
−
1
. This implies that triples, when considering their entire parameter space, yield an important contribution to the overall SN Ia rate.
Abstract
Most massive stars experience binary interactions in their lifetimes that can alter both the surface and core structure of the stripped star with significant effects on their ultimate fate ...as core-collapse supernovae. However, core-collapse supernovae simulations to date have focused almost exclusively on the evolution of single stars. We present a systematic simulation study of single and binary-stripped stars with the same initial mass as candidates for core-collapse supernovae (11–21
M
⊙
). Generally, we find that binary-stripped stars core tend to have a smaller compactness parameter, with a more prominent, deeper silicon/oxygen interface, and explode preferentially to the corresponding single stars of the same initial mass. Such a dichotomy of behavior between these two modes of evolution would have important implications for supernovae statistics, including the final neutron star masses, explosion energies, and nucleosynthetic yields. Binary-stripped remnants are also well poised to populate the possible mass gap between the heaviest neutron stars and the lightest black holes. Our work presents an improvement along two fronts, as we self-consistently account for the pre-collapse stellar evolution and the subsequent explosion outcome. Even so, our results emphasize the need for more detailed stellar evolutionary models to capture the sensitive nature of explosion outcome.
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