SN 2002cx-like and SN Ia-CSM objects show similar early spectra and both belong to a young stellar population, suggesting that they could share the same progenitor origin. Adopting the framework of ...the common-envelope-wind model developed in Meng & Podsiadlowski, we propose that both subclasses of SNe Ia are caused by the explosion of hybrid carbon-oxygen-neon white dwarfs (CONe WDs) in single-degenerate systems, where SNe Ia-CSM explode in systems with a massive common envelope (CE) of ∼1 M , while SN 2002cx-like events correspond to those events where most of the CE has been lost in a wind. Using binary-population-synthesis calculations, we estimate a number ratio of SNe Ia-CSM to SN 2002cx-like objects between 1/3 and 2/3, consistent with observational constraints, and an overall contribution from hybrid CONe WDs to the total SN Ia population that also matches the observed number from these peculiar objects. Our model predicts a statistical sequence of circumstellar material density from SN Ia-CSM to SN 2002cx-like events and normal SNe Ia, consistent with existing radio constraints. We also find a new subclass of hybrid SNe that share the properties of Type II and Type Ia SNe, consistent with some observed SNe, which do not have a surviving companion. In some cases, these could even produce SNe Ia from apparently single WDs.
The era of large transient surveys, gravitational-wave observatories, and multi-messenger astronomy has opened up new possibilities for our understanding of the evolution and final fate of massive ...stars. Most massive stars are born in binary or higher-order multiple systems and exchange mass with a companion star during their lives. In particular, the progenitors of a large fraction of compact-object mergers, and Galactic neutron stars (NSs) and black holes (BHs) have been stripped of their envelopes by a binary companion. Here, we study the evolution of single and stripped binary stars up to core collapse with the stellar evolution code M
ESA
and their final fates with a parametric supernova (SN) model. We find that stripped binary stars can have systematically different pre-SN structures compared to genuine single stars and thus also different SN outcomes. These differences are already established by the end of core helium burning and are preserved up to core collapse. Consequently, we find that Case A and B stripped stars and single and Case C stripped stars develop qualitatively similar pre-SN core structures. We find a non-monotonic pattern of NS and BH formation as a function of CO core mass that is different in single and stripped binary stars. In terms of initial mass, single stars of ≳35
M
⊙
all form BHs, while this transition is only at about 70
M
⊙
in stripped stars. On average, stripped stars give rise to lower NS and BH masses, higher explosion energies, higher kick velocities, and higher nickel yields. Within a simplified population-synthesis model, we show that our results lead to a significant reduction in the rates of BH–NS and BH–BH mergers with respect to typical assumptions made on NS and BH formation. Therefore, our models predict lower detection rates of such merger events with for example the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) than is often considered. Further, we show how certain features in the NS–BH mass distribution of single and stripped stars relate to the chirp-mass distribution of compact object mergers. Further implications of our findings are discussed with respect to the missing red-supergiant problem, a possible mass gap between NSs and BHs, X-ray binaries, and observationally inferred nickel masses from Type Ib/c and IIP SNe.
Detached, symbiotic binaries are generally assumed to interact via Bondi-Hoyle-Littleton (BHL) wind accretion. However, the accretion rates and outflow geometries that result from this mass-transfer ...mechanism cannot adequately explain the observations of the nearest and best studied symbiotic binary, Mira, or the formation of some post-AGB binaries, e.g. barium stars. We propose a new mass-transfer mode for Mira-type binaries, which we call ‘wind Roche-lobe overflow’ (WRLOF), and which we demonstrate with 3D hydrodynamic simulations. Importantly, we show that the circumstellar outflows which result from WRLOF tend to be highly aspherical and strongly focused towards the binary orbital plane. Furthermore, the subsequent mass-transfer rates are at least an order of magnitude greater than the analogous BHL values. We discuss the implications of these results for the shaping of bipolar (proto)-planetary nebulae and other related systems.
The energy budget in common-envelope events (CEEs) is not well understood, with substantial uncertainty even over to what extent the recombination energy stored in ionized hydrogen and helium might ...be used to help envelope ejection. We investigate the reaction of a red giant envelope to heating which mimics limiting cases of energy input provided by the orbital decay of a binary during a CEE, specifically during the post-plunge-in phase during which the spiral-in has been argued to occur on a time-scale longer than dynamical. We show that the outcome of such a CEE depends less on the total amount of energy by which the envelope is heated than on how rapidly the energy was transferred to the envelope and on where the envelope was heated. The envelope always becomes dynamically unstable before receiving net heat energy equal to the envelope's initial binding energy. We find two types of outcome, both of which likely lead to at least partial envelope ejection: 'runaway' solutions in which the expansion of the radius becomes undeniably dynamical, and superficially 'self-regulated' solutions, in which the expansion of the stellar radius stops but a significant fraction of the envelope becomes formally dynamically unstable. Almost the entire reservoir of initial helium recombination energy is used for envelope expansion. Hydrogen recombination is less energetically useful, but is nonetheless important for the development of the dynamical instabilities. However, this result requires the companion to have already plunged deep into the envelope; therefore this release of recombination energy does not help to explain wide post-common-envelope orbits.
The majority of massive stars are expected to exchange mass or merge with a companion during their lives. This immediately implies that most supernovae (SNe) are from such post-mass-exchange objects. ...Here, we explore how mass accretion and merging affect the pre-SN structures of stars and their final fates. To this end, we modelled these complex processes by rapid mass accretion onto stars of different evolutionary stages and followed their evolution up to iron core collapse. We used the stellar evolution code M ESA and inferred the outcome of core-collapse using a neutrino-driven SN model. Our models cover initial masses from 11 to 70 M ⊙ and the accreted mass ranges from 10−200% of the initial mass. All models are non-rotating and for solar metallicity. The rapid accretion model offers a systematic way to approach the landscape of mass accretion and stellar mergers. It is naturally limited in scope and serves as a clean zeroth order baseline for these processes. We find that mass accretion, in particular onto post-main-sequence (post-MS) stars, can lead to a long-lived blue supergiant (BSG) phase during which stars burn helium in their cores. In comparison to genuine single stars, post-MS accretors have small core-to-total mass ratios, regardless of whether they end their lives as BSGs or cool supergiants (CSGs), and they can have genuinely different pre-SN core structures. As in single and binary-stripped stars, we find black-hole (BH) formation for the same characteristic CO core masses M CO of ≈7 M ⊙ and ≳13 M ⊙ . In models with the largest mass accretion, the BH formation landscape as a function of M CO is shifted by about 0.5 M ⊙ to lower masses, that is, such accretors are more difficult to explode. We find a tight relation between our neutron-star (NS) masses and the central entropy of the pre-SN models in all accretors and single stars, suggesting a universal relation that is independent of the evolutionary history of stars. Post-MS accretors explode both as BSGs and CSGs, and we show how to understand their pre-SN locations in the Hertzsprung-Russell (HR) diagram. Accretors exploding as CSGs can have much higher envelope masses than single stars. Some BSGs that avoid the luminous-blue-variable (LBV) regime in the HR diagram are predicted to collapse into BHs of up to 50 M ⊙ , while others explode in SNe and eject up to 40 M ⊙ , greatly exceeding ejecta masses from single stars. Both the BH and SN ejecta masses increase to about 80 M ⊙ in our models when allowing for multiple mergers, for example, in initial triple-star systems, and they can be even higher at lower metallicities. Such high BH masses may fall into the pair-instability-SN mass gap and could help explain binary BH mergers involving very massive BHs as observed in GW190521. We further find that some of the BSG models explode as LBVs, which may lead to interacting SNe and possibly even superluminous SNe.
We use a collection of 14 well-measured neutron-star masses to strengthen the case that a substantial fraction of these neutron stars were formed via electron-capture (e-capture) supernovae (SNe) as ...opposed to Fe core-collapse SNe. The e-capture SNe are characterized by lower resultant gravitational masses and smaller natal kicks, leading to lower orbital eccentricities when the e-capture SN has led to the formation of the second neutron star in a binary system. Based on the measured masses and eccentricities, we identify four neutron stars, which have a mean post-collapse gravitational mass of {approx}1.25 M {sub sun}, as the product of e-capture SNe. We associate the remaining 10 neutron stars, which have a mean mass of {approx}1.35 M {sub sun}, with Fe core-collapse SNe. If the e-capture SN occurs during the formation of the first neutron star, then this should substantially increase the formation probability for double neutron stars, given that more systems will remain bound with the smaller kicks. However, this does not appear to be the case for any of the observed systems and we discuss possible reasons for this.
ABSTRACT
During the first three observing runs of the Advanced gravitational-wave detector network, the LIGO/Virgo collaboration detected several black hole binary (BHBH) mergers. As the population ...of detected BHBH mergers grows, it will become possible to constrain different channels for their formation. Here we consider the chemically homogeneous evolution (CHE) channel in close binaries, by performing population synthesis simulations that combine realistic binary models with detailed cosmological calculations of the chemical and star-formation history of the Universe. This allows us to constrain population properties, as well as cosmological and aLIGO/aVirgo detection rates of BHBH mergers formed through this pathway. We predict a BHBH merger rate at redshift zero of $5.8 \textrm {Gpc}^{-3} \textrm {yr}^{-1}$ through the CHE channel, to be compared with aLIGO/aVirgo’s measured rate of ${53.2}_{-28.2}^{+55.8} \text{Gpc}^{-3}\text{yr}^{-1}$, and find that eventual merger systems have BH masses in the range $17{-}43 \,\textrm {M}_{\odot }$ below the pair-instability supernova (PISN) gap, and ${\gt}124 \textrm {M}_{\odot }$ above the PISN gap. We investigate effects of momentum kicks during black hole formation, and calculate cosmological and magnitude limited PISN rates. We also study the effects of high-redshift deviations in the star formation rate. We find that momentum kicks tend to increase delay times of BHBH systems, and our magnitude limited PISN rate estimates indicate that current deep surveys should be able to detect such events. Lastly, we find that our cosmological merger rate estimates change by at most ${\sim}8{{\ \rm per\ cent}}$ for mild deviations of the star formation rate in the early Universe, and by up to ${\sim}40\,\text{per cent}$ for extreme deviations.
A massive star can explode in powerful supernova (SN) and form a neutron star, but it may also collapse directly into a black hole. Understanding and predicting the final fate of such stars is ...increasingly important, for instance, in the context of gravitational-wave astronomy. The interior mixing of stars (in general) and convective boundary mixing (in particular) remain some of the largest uncertainties in their evolution. Here, we investigate the influence of convective boundary mixing on the pre-SN structure and explosion properties of massive stars. Using the 1D stellar evolution code M ESA , we modeled single, non-rotating stars of solar metallicity, with initial masses of 5 − 70 M ⊙ and convective core step-overshooting of 0.05 − 0.50 pressure scale heights. Stars were evolved until the onset of iron core collapse and the pre-SN models were exploded using a parametric, semi-analytic SN code. We used the compactness parameter to describe the interior structure of stars at core collapse and we found a pronounced peak in compactness at carbon-oxygen core masses of M CO ≈ 7 M ⊙ , along with generally high compactness at M CO ≳ 14 M ⊙ . Larger convective core overshooting will shift the location of the compactness peak by 1 − 2 M ⊙ to higher M CO . These core masses correspond to initial masses of 24 M ⊙ (19 M ⊙ ) and ≳40 M ⊙ (≳30 M ⊙ ), respectively, in models with the lowest (highest) convective core overshooting parameter. In both high-compactness regimes, stars are found to collapse into black holes. As the luminosity of the pre-supernova progenitor is determined by M CO , we predict black hole formation for progenitors with luminosities of 5.35 ≤ log( L / L ⊙ )≤5.50 and log( L / L ⊙ )≥5.80. The luminosity range of black hole formation from stars in the compactness peak is in good agreement with the observed luminosity of the red supergiant star N6946 BH1, which disappeared without a bright supernova, indicating that it had likely collapsed into a black hole. While some of our models in the luminosity range of log( L / L ⊙ ) = 5.1 − 5.5 do indeed collapse to form black holes, this does not fully explain the lack of observed SN IIP progenitors at these luminosities. This case specifically refers to the “missing red supergiant” problem. The amount of convective boundary mixing also affects the wind mass loss of stars, such that the lowest black hole masses are 15 M ⊙ and 10 M ⊙ in our models, with the lowest and highest convective core overshooting parameter, respectively. The compactness parameter, central specific entropy, and iron core mass describe a qualitatively similar landscape as a function of M CO , and we find that entropy is a particularly good predictor of the neutron-star masses in our models. We find no correlation between the explosion energy, kick velocity, and nickel mass production with the convective core overshooting value, but we do see a tight relation with the compactness parameter. Furthermore, we show how convective core overshooting affects the pre-supernova locations of stars in the Hertzsprung–Russell diagram (HRD) and the plateau luminosity and duration of SN IIP light curves.
Recent discoveries of weak and fast optical transients raise the question of their origin. We investigate the minimum ejecta mass associated with core-collapse supernovae (SNe) of Type Ic. We show ...that mass transfer from a helium star to a compact companion can produce an ultra-stripped core which undergoes iron core collapse and leads to an extremely fast and faint SN Ic. In this Letter, a detailed example is presented in which the pre-SN stellar mass is barely above the Chandrasekhar limit, resulting in the ejection of only ~0.05-0.20 M sub(middot in circle) of material and the formation of a low-mass neutron star (NS). We compute synthetic light curves of this case and demonstrate that SN 2005ek could be explained by our model. We estimate that the fraction of such ultra-stripped to all SNe could be as high as 10 super(?3)-10 super(?2). Finally, we argue that the second explosion in some double NS systems (for example, the double pulsar PSR J0737?3039B) was likely associated with an ultra-stripped SN Ic.
The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analog of large star-formation events in the distant universe. We determined the recent formation history and the initial ...mass function (IMF) of massive stars in 30 Doradus on the basis of spectroscopic observations of 247 stars more massive than 15 solar masses (Formula: see text). The main episode of massive star formation began about 8 million years (My) ago, and the star-formation rate seems to have declined in the last 1 My. The IMF is densely sampled up to 200 Formula: see text and contains 32 ± 12% more stars above 30 Formula: see text than predicted by a standard Salpeter IMF. In the mass range of 15 to 200 Formula: see text, the IMF power-law exponent is Formula: see text, shallower than the Salpeter value of 2.35.
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