arXiv subjects

Ph. Podsiadlowski

Publications and source records attributed to Ph. Podsiadlowski.

At least 19 recordsLinked to original sources

arXiv2025

New gravitational-wave data support a bimodal black-hole mass distribution

Detailed stellar evolution and supernova models yield a bimodal black-hole mass distribution with a narrow peak around 10 solar masses from stars within a narrow range of progenitor properties and a second broader peak starting around 20 solar masses from very massive progenitors. This bimodal black-hole mass distribution leads to a characteristic distribution of chirp masses of merging binary black holes, with two main peaks arising from the merger of two black holes where both come either from the low- or the high-mass peak and a smaller peak in between from the mixed merger of a low-mass and a high-mass black hole. We carry out a population synthesis study of binary black hole formation and compare the results to the observed chirp masses of gravitational-wave events. We find that only the bimodal black-hole mass prescription is able to reproduce the structure of peaks and gaps in the observed chirp-mass distribution, which is not matched by predictions from other remnant mass prescriptions in the literature.

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arXiv2025

Explosions of pulsating red supergiants: a natural pathway for the diversity of Type II-P/L supernovae

Red supergiants (RSGs), which are progenitors of hydrogen-rich Type II supernovae (SNe), have been known to pulsate from both observations and theory. The pulsations can be present at core collapse and affect the resulting SN. However, SN light curve models of such RSGs commonly use hydrostatic progenitor models and ignore pulsations. Here, we model the final stages of a 15 solar-mass RSG and self-consistently follow the hydrodynamical evolution. We find the growth of large amplitude radial pulsations in the envelope. After a transient phase where the envelope restructures, the pulsations settle to a steady and periodic oscillation with a period of 817 days. We show that they are driven by the $κγ$-mechanism, which is an interplay between changing opacities and the release of recombination energy of hydrogen and helium. This leads to complex and non-coherent expansion and contraction in different parts of the envelope, which greatly affect the SN progenitor properties, including its location in the Hertzsprung-Russell diagram. We simulate SN explosions of this model at different pulsations phases. Explosions in the compressed state result in a flat light curve (Type II-P). In contrast, the SN light curve in the expanded state declines rapidly, reminiscent of a Type II-L SN. For cases in between, we find light curves with various decline rates. Features in the SN light curves are directly connected to features in the density profiles. These are in turn linked to the envelope ionization structure, which is the driving mechanism of the pulsations. We predict that some of the observed diversity in Type II SN light curves can be explained by RSG pulsations. For more massive RSGs, we expect stronger pulsations that might even lead to dynamical mass ejections of the envelope and to an increased diversity in SN light curves.

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arXiv2025

Supernovae from stellar mergers and accretors of binary mass transfer: Implications for Type IIP, 1987A-like and interacting supernovae

As most massive stars are born in binary and other multiple-star systems, many are expected to exchange mass with a companion star or merge with it during their lives. This means that most supernovae (SNe) are from such binary products. Here, we focus on hydrogen-rich Type II SNe from accretors of binary mass transfer and stellar mergers. We compute various SN properties such as the explosion energies, nickel yields, and neutron star (NS) kick velocities, but also consider NS masses. We find tight correlations between these parameters and, e.g., the central specific entropy and core compactness. However, there is no obvious relation between these explosion properties and the evolutionary history of the pre-SN stars. We find linear relations between the nickel mass and the SN explosion energy and the NS remnant mass. We further group our models into progenitors of SNe IIP, SN 1987A-like and interacting SNe, predict their SN and SN-progenitor properties and compare to observations. Accretors of binary mass transfer and stellar mergers naturally produce SNe IIP with long plateau durations from progenitors with relatively small CO-cores but large envelope masses (c.f. SN 2015ba). Our models give rise to tight relations between the plateau luminosity and the nickel mass as well as the SN ejecta velocity as inferred observationally for SNe IIP. We speculate that cool/red supergiants at $\log\,L/L_\odot\,{\geq}\,5.5$ encounter enhanced mass loss due to envelope instabilities and could then explode in interacting SNe IIn. The rate of such SNe from our models seems compatible with observations. Some of our binary models explode as $10^6\,L_\odot$ blue supergiants that may have encountered enhanced and/or eruptive mass loss shortly before their SNe and could thus help understand interacting SNe such as SN 1961V and SN 2005gl but also superluminous Type II SNe such as SN 2010jl. [abridged]

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arXiv2024

Going from 3D common-envelope simulations to fast 1D simulations

One-dimensional (1D) methods for simulating the common-envelope (CE) phase offer advantages over three-dimensional (3D) simulations regarding their computational speed and feasibility. We present the 1D CE method from Bronner et al. (2024), including the results of the CE simulations of an asymptotic giant branch star donor. We further test this method in the massive star regime by computing the CE event of a red supergiant with a neutron-star mass and a black-hole mass companion. The 1D model can reproduce the orbital evolution and the envelope ejection from 3D simulations when choosing suitable values for the free parameters in the model. The best-fitting values differ from the expectations based on the low mass simulations, indicating that the free parameters depend on the structure of the giant star. The released recombination energy from hydrogen and helium helps to expand the envelope, similar to the low-mass CE simulations.

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arXiv2024

It's written in the massive stars: The role of stellar physics in the formation of black holes

In the age of gravitational-wave (GW) sources and newly discovered local black holes (BH) and neutron stars (NS), understanding the fate of stars is a key question. Not every massive star is expected to successfully explode as a supernova and leave behind a NS; some stars form BHs. The remnant depends on explosion physics but also on the final core structure, often summarized by the compactness parameter or iron core mass, where high values have been linked to BH formation. Several groups have reported similar patterns in these parameters as a function of mass, characterized by a prominent compactness peak followed by another peak at higher masses, pointing to a common underlying physical mechanism. Here, we investigate its origin by computing single-star models from 17 to 50 solar masses with MESA. The first and second compactness increases originate from core carbon and neon burning, respectively, becoming neutrino dominated, which enhances the core contraction and ultimately increases the iron-core mass and compactness. An early core neon ignition during carbon burning, and an early silicon ignition during oxygen burning help counter the core contraction and decrease the final iron core mass and compactness. Shell mergers between C/Ne and O-burning shells further decrease the compactness and we show that they are due to an enhanced entropy production in these layers. We find that the final structure of massive stars is not random but already written in their cores at core helium exhaustion. The same mechanisms determine the final structure of any star in this core mass range, including binary products, though binary interactions systematical shift the range of expected BH formation. Finally, we discuss the role of stellar physics uncertainties and how to apply these findings to studies of GW sources. [Abridged]

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arXiv2024

Pre-supernova evolution and final fate of stellar mergers and accretors of binary mass transfer

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. We use the stellar evolution code MESA, infer the outcome of core-collapse using a neutrino-driven SN model, and apply a rapid-accretion model. Our models cover initial masses from 11 to 70 Msun and the accreted mass ranges from 10-200% of the initial mass. We find that mass accretion in particular onto post-main-sequence (post-MS) stars can lead to a long-lived blue supergiant (BSG) phase. 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 Msun and >13 Msun. In models with the largest mass accretion, the BH-formation landscape as a function of M_CO is shifted by about 0.5 Msun to lower masses. We find a tight relation between our neutron-star (NS) masses and the central entropy of the pre-SN models, 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 diagram. Some BSGs that avoid the luminous-blue-variable (LBV) regime are predicted to collapse into BHs of up to 50 Msun while others explode in supernovae and eject up to 40 Msun, greatly exceeding ejecta masses from single stars. These masses can be even higher at lower metallicities, and they may fall into the pair-instability-supernova mass gap. [abridged]

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arXiv2023

Going from 3D to 1D: A one-dimensional approach to common-envelope evolution

The common-envelope (CE) phase is a crucial stage in binary star evolution because the orbital separation can shrink drastically while ejecting the envelope of a giant star. Three-dimensional (3D) hydrodynamic simulations of CE evolution are indispensable to learning about the mechanisms that play a role during the CE phase. While these simulations offer great insight, they are computationally expensive. We propose a one-dimensional (1D) model to simulate the CE phase within the stellar evolution code $\texttt{MESA}$ by using a parametric drag force prescription for dynamical drag and adding the released orbital energy as heat into the envelope. We compute CE events of a $0.97\,\mathrm{M}_\odot$ asymptotic giant-branch star and a point mass companion with mass ratios of 0.25, 0.50, and 0.75, and compare them to 3D simulations of the same setup. The 1D CE model contains two free parameters, which we demonstrate are both needed to fit the spiral-in behavior and the fraction of ejected envelope mass of the 1D method to the 3D simulations. For mass ratios of 0.25 and 0.50, we find good-fitting 1D simulations, while for a mass ratio of 0.75, we do not find a satisfactory fit to the 3D simulation as some of the assumptions in the 1D method are no longer valid. In all our simulations, we find that the released recombination energy is important to accelerate the envelope and drive the ejection.

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arXiv2023

Convective-core overshooting and the final fate of massive stars

Massive stars can explode in powerful supernovae (SNe) forming neutron stars but they may also collapse directly into black holes (BHs). Understanding and predicting their final fate is increasingly important, e.g, in the context of gravitational-wave astronomy. The interior mixing of stars in general and convective boundary mixing 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 Mesa, we model single, non-rotating stars of solar metallicity with initial masses of $5-70\mathrm{M_\odot}$ and convective core step-overshooting of $0.05-0.50H_\mathrm{P}$. Stars are evolved until the onset of iron core collapse, and the pre-SN models are exploded using a parametric, semi-analytic SN code. We use the compactness parameter to describe the interior structure of stars at core collapse. Larger convective core overshooting shifts the location of the compactness peak by $1-2\mathrm{M_\odot}$ to higher $M_\mathrm{CO}$. As the luminosity of the pre-SN progenitor is determined by $M_\mathrm{CO}$, we predict BH formation for progenitors with luminosities $5.35<\log(L/\mathrm{L_\odot})<5.50$ and $\log(L/\mathrm{L_\odot})>5.80$. The luminosity range of BH formation agrees well with the observed luminosity of the red supergiant star N6946BH1 that disappeared without a bright SN and likely collapsed into a BH. While some of our models in the luminosity range $\log(L/\mathrm{L_\odot})=5.1-5.5$ indeed collapse to form BHs, this does not fully explain the lack of observed SN~IIP progenitors at these luminosities, ie the missing red-supergiant problem. Convective core overshooting affects the BH masses, the pre-SN location of stars in the Hertzsprung-Russell diagram, the plateau luminosity and duration of SN~IIP lightcurves.[Abridged]

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arXiv2022

Properties and applications of a predicted population of runaway He-sdO/B stars ejected from single degenerate He-donor SNe

This study builds on previous works, producing the most extensive prediction of the properties of such a hypothetical population to date, taking into account both Chandrasekhar and non-Chandrasekhar mass events. These results are then used to define criteria for membership of this population and characterise putative subpopulations This study contains 6x10^6 individual ejection trajectories out of the Galactic plane calculated with the stellar kinematics framework SHyRT, which are analysed with regard to their bulk observational properties. These are then put into context with the only previously identified population member US\,708 and applied to a number of other possible candidate objects. We find that two additional previously observed objects possess properties to warrant a designation as candidate objects. Characterisation of these object with respect to the predicted population finds all of them to be extreme in at least one astrometric observable. We find that current observations support a Galactic SN rate on the order of ~3x10^-7/yr to ~2x10^-6/yr, three orders of magnitude below the inferred Galactic SN Ia rate and two orders of magnitude below the formation rate of predicted He-donor progenitors. The number of currently observed population members suggests that the He-donor scenariois not a dominant contributor to the number of observed SNe Ia. However, we find that, even at the low event rate suggested, the majority of possibly detectable population members is still undetected. The extreme nature of current population members suggests that a still larger number of objects has simply evaded detection up to this point, hinting at a higher contribution than is currently supported by observation. - abridged -

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arXiv2020

Pre-supernova evolution, compact object masses and explosion properties of stripped binary stars

Most massive stars are born in binary or higher-order multiple systems and exchange mass with a companion 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 off 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 MESA 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. The bases of these differences are already established by the end of core helium burning and are preserved up to core collapse. 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 masses, single stars of >35 Msun all form BHs, while this transition is only at 70 Msun 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 of the rates of BH-NS and BH-BH mergers with respect to typical assumptions made on NS and BH formation. Therefore, we predict lower detection rates of such merger events by, e.g., advanced LIGO than is often considered. We further show how 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. [abridged]

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arXiv2020

Long-term evolution of a magnetic massive merger product

About 10% of stars more massive than ${\approx}\,1.5\,\mathrm{M}_\odot$ have strong, large-scale surface magnetic fields and are being discussed as progenitors of highly-magnetic white dwarfs and magnetars. The origin of these fields remains uncertain. Recent 3D magnetohydrodynamical simulations have shown that strong magnetic fields can be generated in the merger of two massive stars. Here, we follow the long-term evolution of such a 3D merger product in a 1D stellar evolution code. During a thermal relaxation phase after the coalescence, the merger product reaches critical surface rotation, sheds mass and then spins down primarily because of internal mass readjustments. The spin of the merger product after thermal relaxation is mainly set by the co-evolution of the star-torus structure left after coalescence. This evolution is still uncertain, so we also consider magnetic braking and other angular-momentum-gain and -loss mechanisms that may influence the final spin of the merged star. Because of core compression and mixing of carbon and nitrogen in the merger, enhanced nuclear burning drives a transient convective core that greatly contributes to the rejuvenation of the star. Once the merger product relaxed back to the main sequence, it continues its evolution similar to that of a genuine single star of comparable mass. It is a slow rotator that matches the magnetic blue straggler $τ$ Sco. Our results show that merging is a promising mechanism to explain some magnetic massive stars and it may also be key to understand the origin of the strong magnetic fields of highly-magnetic white dwarfs and magnetars.

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arXiv2018

Response to comment on "An excess of massive stars in the local 30 Doradus starburst"

Farr and Mandel reanalyse our data, finding initial-mass-function slopes for high mass stars in 30 Doradus that agree with our results. However, their reanalysis appears to underpredict the observed number of massive stars. Their technique results in more precise slopes than in our work, strengthening our conclusion that there is an excess of massive stars above $30\,\mathrm{M}_\odot$ in 30 Doradus.

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arXiv2018

Do SN 2002cx-like and SN Ia-CSM objects share the same origin?

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 (CEW) model developed in \citet{MENGXC17}, we here 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 $\sim1~M_{\odot}$, while SN 2002cx-like events correspond to those events where most of the CE has been lost in a wind. Using binary-population-synthesis (BPS) calculations, we estimate a number ratio of SNe Ia-CSM to SN 2002cx-like objects between $\frac{1}{3}$ and $\frac{2}{3}$, 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 CSM 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 which 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.

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arXiv2018

An excess of massive stars in the local 30 Doradus starburst

The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analogue of large star-formation events in the distant Universe. We determine the recent formation history and the initial mass function (IMF) of massive stars in 30 Doradus based on spectroscopic observations of 247 stars more massive than 15 solar masses ($\mathrm{M}_\odot$). The main episode of massive star formation started about $8\,\mathrm{Myr}$ ago and the star-formation rate seems to have declined in the last $1\,\mathrm{Myr}$. The IMF is densely sampled up to $200\,\mathrm{M}_\odot$ and contains $32\pm12\%$ more stars above $30\,\mathrm{M}_\odot$ than predicted by a standard Salpeter IMF. In the mass range $15-200\,\mathrm{M}_\odot$, the IMF power-law exponent is $1.90^{+0.37}_{-0.26}$, shallower than the Salpeter value of 2.35.

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arXiv2017

A kilonova as the electromagnetic counterpart to a gravitational-wave source

Gravitational waves were discovered with the detection of binary black hole mergers and they should also be detectable from lower mass neutron star mergers. These are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal called a kilonova. The gravitational wave source GW170817 arose from a binary neutron star merger in the nearby Universe with a relatively well confined sky position and distance estimate. Here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy NGC4993, which is spatially coincident with GW170817 and a weak short gamma-ray burst. The transient has physical parameters broadly matching the theoretical predictions of blue kilonovae from neutron star mergers. The emitted electromagnetic radiation can be explained with an ejected mass of 0.04 +/- 0.01 Msol, with an opacity of kappa <= 0.5 cm2/gm at a velocity of 0.2 +/- 0.1c. The power source is constrained to have a power law slope of beta = -1.2 +/- 0.3, consistent with radioactive powering from r-process nuclides. We identify line features in the spectra that are consistent with light r-process elements (90 < A < 140). As it fades, the transient rapidly becomes red, and emission may have contribution by a higher opacity, lanthanide-rich ejecta component. This indicates that neutron star mergers produce gravitational waves, radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements.

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arXiv2017

Formation of Double Neutron Star Systems

Double neutron star (DNS) systems represent extreme physical objects and the endpoint of an exotic journey of stellar evolution and binary interactions. Large numbers of DNS systems and their mergers are anticipated to be discovered using the Square-Kilometre-Array searching for radio pulsars and high-frequency gravitational wave detectors (LIGO/VIRGO), respectively. Here we discuss all key properties of DNS systems, as well as selection effects, and combine the latest observational data with new theoretical progress on various physical processes with the aim of advancing our knowledge on their formation. We examine key interactions of their progenitor systems and evaluate their accretion history during the high-mass X-ray binary stage, the common envelope phase and the subsequent Case BB mass transfer, and argue that the first-formed NSs have accreted at most $\sim 0.02\;M_{\odot}$. We investigate DNS masses, spins and velocities, and in particular correlations between spin period, orbital period and eccentricity. Numerous Monte Carlo simulations of the second supernova (SN) events are performed to extrapolate pre-SN stellar properties and probe the explosions. All known close-orbit DNS systems are consistent with ultra-stripped exploding stars. Although their resulting NS kicks are often small, we demonstrate a large spread in kick magnitudes which may, in general, depend on the past interaction history of the exploding star and thus correlate with the NS mass. We analyze and discuss NS kick directions based on our SN simulations. Finally, we discuss the terminal evolution of close-orbit DNS systems until they merge and possibly produce a short $γ$-ray burst.

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arXiv2017

A common-envelope wind model for Type Ia supernovae (I): binary evolution and birth rate

The single-degenerate (SD) model is one of the principal models for the progenitors of type Ia supernovae (SNe Ia), but some of the predictions in the most widely studied version of the SD model, i.e. the optically thick wind (OTW) model, have not been confirmed by observations. Here, we propose a new version of the SD model in which a common envelope (CE) is assumed to form when the mass-transfer rate between a carbon-oxygen white dwarf (CO WD) and its companion exceeds a critical accretion rate. The WD may gradually increase its mass at the base of the CE. Due to the large nuclear luminosity for stable hydrogen burning, the CE may expand to giant dimensions and will lose mass from the surface of the CE by a CE wind (CEW). Because of the low CE density, the binary system will avoid a fast spiral-in phase and finally re-emerge from the CE phase. Our model may share the virtues of the OTW model but avoid some of its shortcomings. We performed binary stellar evolution calculations for more than 1100 close WD + MS binaries. Compared with the OTW model, the parameter space for SNe Ia from our CEW model extends to more massive companions and less massive WDs. Correspondingly, the Galactic birth rate from the CEW model is higher than that from the OTW model by $\sim$30\%. Finally, we discuss the uncertainties of the CEW model and the differences between our CEW model and the OTW model.

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arXiv2016

Common envelope ejection in massive binary stars - Implications for the progenitors of GW150914 and GW151226

The recently detected gravitational wave signals (GW150914 and GW151226) of the merger event of a pair of relatively massive stellar-mass black holes (BHs) calls for an investigation of the formation of such progenitor systems in general. We analyse the common envelope (CE) stage of the "traditional" formation channel in binaries where the first-formed compact object undergoes an in-spiral inside the envelope of its evolved companion star and ejects the envelope in that process. We calculate envelope binding energies of donor stars with initial masses between 4 and 115 Msun for metallicities of Z=Zsun/2 and Z=Zsun/50, and derive minimum masses of in-spiralling objects needed to eject these envelopes. We find that CE evolution, besides from producing WD-WD and NS-NS binaries, may, in principle, also produce massive BH-BH systems with individual BH component masses up to ~50-60 Msun, in particular for donor stars evolved to giants. However, the physics of envelope ejection of massive stars remains uncertain. We discuss the applicability of the energy-budget formalism, the location of the bifurcation point, the recombination energy and the accretion energy during in-spiral as possible energy sources, and also comment on the effect of inflated helium cores. Massive stars in a wide range of metallicities and with initial masses up to at least 115 Msun may possibly shed their envelopes and survive CE evolution, depending on their initial orbital parameters, similarly to the situation for intermediate mass and low-mass stars with degenerate cores. We conclude that based on stellar structure calculations, and in the view of the usual simple energy budget analysis, events like GW150914 and GW151226 could possibly be produced from the CE channel. Calculations of post-CE orbital separations, however, and thus the estimated LIGO detection rates, remain highly uncertain. [Abridged]

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