Detections of gravitational waves are now starting to probe the mass distribution of stellar mass black holes (BHs). Robust predictions from stellar models are needed to interpret these. Theory ...predicts the existence of a gap in the BH mass distribution because of pair-instability supernovae. The maximum BH mass below the gap is the result of pulsational mass loss. We evolve massive helium stars through their late hydrodynamical phases of evolution using the open-source MESA stellar evolution code. We find that the location of the lower edge of the mass gap at 45 is remarkably robust against variations in the metallicity ( 3 ), the treatment of internal mixing ( 1 ), and stellar wind mass loss ( 4 ), making it the most robust predictor for the final stages of the evolution of massive stars. The reason is that the onset of the instability is dictated by the near-final core mass, which in turn sets the resulting BH mass. However, varying the reaction rate within its 1 uncertainties shifts the location of the gap between 40 and 56 . We provide updated analytic fits for population synthesis simulations. Our results imply that the detection of merging BHs can provide constraints on nuclear astrophysics. Furthermore, the robustness against metallicity suggests that there is a universal maximum for the location of the lower edge of the gap, which is insensitive to the formation environment and redshift for first-generation BHs. This is promising for the possibility to use the location of the gap as a "standard siren" across the universe.
Self-induced electricity, including lightning, is often observed in dusty atmospheres. However, the physical mechanisms leading to this phenomenon remain elusive as they are remarkably challenging to ...determine due to the high complexity of the multi-phase turbulent flows involved. Using a fast multi-pole method in direct numerical simulations of homogeneous turbulence laden with hundreds of millions of inertial particles, here we show that mesoscopic electric fields can be aerodynamically created in bi-disperse suspensions of oppositely charged particles. The generation mechanism is self-regulating and relies on turbulence preferentially concentrating particles of one sign in clouds while dispersing the others more uniformly. The resulting electric field varies over much larger length scales than both the mean inter-particle spacing and the size of the smallest eddies. Scaling analyses suggest that low ambient pressures, such as those prevailing in the atmosphere of Mars, increase the dynamical relevance of this aerodynamic mechanism for electrical breakdown.
Abstract
Most massive stars are born in binaries close enough for mass transfer episodes. These modify the appearance, structure, and future evolution of both stars. We compute the evolution of a ...100-day-period binary, consisting initially of a 25
M
⊙
star and a 17
M
⊙
star, which experiences stable mass transfer. We focus on the impact of mass accretion on the surface composition, internal rotation, and structure of the accretor. To anchor our models, we show that our accretor broadly reproduces the properties of
ζ
Ophiuchi, which has long been proposed to have accreted mass before being ejected as a runaway star when the companion exploded. We compare our accretor to models of single rotating stars and find that the later and stronger spin-up provided by mass accretion produces significant differences. Specifically, the core of the accretor retains higher spin at the end of the main sequence, and a convective layer develops that changes its density profile. Moreover, the surface of the accretor star is polluted by CNO-processed material donated by the companion. Our models show effects of mass accretion in binaries that are not captured in single rotating stellar models. This possibly impacts the further evolution (either in a binary or as single stars), the final collapse, and the resulting spin of the compact object.
Gravitational-wave detections are starting to allow us to probe the physical processes in the evolution of very massive stars through the imprints they leave on their final remnants. Stellar ...evolution theory predicts the existence of a gap in the black hole mass distribution at high mass due to the effects of pair instability. Previously, we showed that the location of the gap is robust against model uncertainties, but it does depend sensitively on the uncertain rate. This rate is of great astrophysical significance and governs the production of oxygen at the expense of carbon. We use the open-source MESA stellar evolution code to evolve massive helium stars to probe the location of the mass gap. We find that the maximum black hole mass below the gap varies between and , depending on the strength of the uncertain reaction rate. With the first 10 gravitational-wave detections of black holes, we constrain the astrophysical S-factor for , at , to at 68% confidence. With detected binary black hole mergers, we expect to constrain the S-factor to within 10-30 . We also highlight a role for independent constraints from electromagnetic transient surveys. The unambiguous detection of pulsational pair-instability supernovae would imply that . Degeneracies with other model uncertainties need to be investigated further, but probing nuclear stellar astrophysics poses a promising science case for the future gravitational-wave detectors.
The majority of massive stars live in binary or multiple systems and will interact with a companion during their lifetimes, which helps to explain the observed diversity of core-collapse supernovae. ...Donor stars in binary systems can lose most of their hydrogen-rich envelopes through mass transfer. As a result, not only are the surface properties affected, but so is the core structure. However, most calculations of the core-collapse properties of massive stars rely on single-star models. We present a systematic study of the difference between the pre-supernova structures of single stars and stars of the same initial mass (11–21
M
⊙
) that have been stripped due to stable post-main-sequence mass transfer at solar metallicity. We present the pre-supernova core composition with novel diagrams that give an intuitive representation of the isotope distribution. As shown in previous studies, at the edge of the carbon-oxygen core, the binary-stripped star models contain an extended gradient of carbon, oxygen, and neon. This layer remains until core collapse and is more extended in mass for higher initial stellar masses. It originates from the receding of the convective helium core during core helium burning in binary-stripped stars, which does not occur in single-star models. We find that this same evolutionary phase leads to systematic differences in the final density and nuclear energy generation profiles. Binary-stripped star models have systematically higher total masses of carbon at the moment of core collapse compared to single-star models, which likely results in systematically different supernova yields. In about half of our models, the silicon-burning and oxygen-rich layers merge after core silicon burning. We discuss the implications of our findings for the “explodability”, supernova observations, and nucleosynthesis of these stars. Our models are publicly available and can be readily used as input for detailed supernova simulations.
Mass loss processes are a key uncertainty in the evolution of massive stars. They determine the amount of mass and angular momentum retained by the star, thus influencing its evolution and ...presupernova structure. Because of the high complexity of the physical processes driving mass loss, stellar evolution calculations must employ parametric algorithms, and usually only include wind mass loss. We carried out an extensive parameter study of wind mass loss and its effects on massive star evolution using the open-source stellar evolution code MESA. We provide a systematic comparison of wind mass loss algorithms for solar-metallicity, nonrotating, single stars in the initial mass range of 15 M⊙ to 35 M⊙. We consider combinations drawn from two hot phase (i.e., roughly the main sequence) algorithms, three cool phase (i.e., post-main-sequence) algorithms, and two Wolf-Rayet mass loss algorithms. We discuss separately the effects of mass loss in each of these phases. In addition, we consider linear wind efficiency scale factors of 1, 0.33, and 0.1 to account for suggested reductions in mass loss rates due to wind inhomogeneities. We find that the initial to final mass mapping for each zero-age main-sequence (ZAMS) mass has a ~ 50% uncertainty if all algorithm combinations and wind efficiencies are considered. The ad-hoc efficiency scale factor dominates this uncertainty. While the final total mass and internal structure of our models vary tremendously with mass loss treatment, final luminosity and effective temperature are much less sensitive for stars with ZAMS mass ≲ 30 M⊙. This indicates that uncertainty in wind mass loss does not negatively affect estimates of the ZAMS mass of most single-star supernova progenitors from pre-explosion observations. Our results furthermore show that the internal structure of presupernova stars is sensitive to variations in both main sequence and post main-sequence mass loss. The compactness parameter ξ ∝ ℳ /R(ℳ) has been identified as a proxy for the “explodability” of a given presupernova model. We find that ξ varies by as much as 30% for models of the same ZAMS mass evolved with different wind efficiencies and mass loss algorithm combinations. This suggests that the details of the mass loss treatment might bias the outcome of detailed core-collapse supernova calculations and the predictions for neutron star and black hole formation.
Abstract
Gravitational-wave detectors are starting to reveal the redshift evolution of the binary black hole (BBH) merger rate,
R
BBH
(
z
). We make predictions for
R
BBH
(
z
) as a function of black ...hole mass for systems originating from isolated binaries. To this end, we investigate correlations between the delay time and black hole mass by means of the suite of binary population synthesis simulations,
COMPAS
. We distinguish two channels: the common envelope (CE), and the stable Roche-lobe overflow (RLOF) channel, characterized by whether the system has experienced a common envelope or not. We find that the CE channel preferentially produces BHs with masses below about 30
M
⊙
and short delay times (
t
delay
≲ 1 Gyr), while the stable RLOF channel primarily forms systems with BH masses above 30
M
⊙
and long delay times (
t
delay
≳ 1 Gyr). We provide a new fit for the metallicity-dependent specific star formation rate density based on the Illustris TNG simulations, and use this to convert the delay time distributions into a prediction of
R
BBH
(
z
). This leads to a distinct redshift evolution of
R
BBH
(
z
) for high and low primary BH masses. We furthermore find that, at high redshift,
R
BBH
(
z
) is dominated by the CE channel, while at low redshift, it contains a large contribution (∼40%) from the stable RLOF channel. Our results predict that, for increasing redshifts, BBHs with component masses above 30
M
⊙
will become increasingly scarce relative to less massive BBH systems. Evidence of this distinct evolution of
R
BBH
(
z
) for different BH masses can be tested with future detectors.
ABSTRACT
Gravitational-wave detections are now probing the black hole (BH) mass distribution, including the predicted pair-instability mass gap. These data require robust quantitative predictions, ...which are challenging to obtain. The most massive BH progenitors experience episodic mass ejections on time-scales shorter than the convective turnover time-scale. This invalidates the steady-state assumption on which the classic mixing length theory relies. We compare the final BH masses computed with two different versions of the stellar evolutionary code $\tt{MESA}$: (i) using the default implementation of Paxton et al. (2018) and (ii) solving an additional equation accounting for the time-scale for convective deceleration. In the second grid, where stronger convection develops during the pulses and carries part of the energy, we find weaker pulses. This leads to lower amounts of mass being ejected and thus higher final BH masses of up to ∼$5\, \mathrm{M}_\odot$. The differences are much smaller for the progenitors that determine the maximum mass of BHs below the gap. This prediction is robust at $M_{\rm BH, max}\simeq 48\, \mathrm{M}_\odot$, at least within the idealized context of this study. This is an encouraging indication that current models are robust enough for comparison with the present-day gravitational-wave detections. However, the large differences between individual models emphasize the importance of improving the treatment of convection in stellar models, especially in the light of the data anticipated from the third generation of gravitational-wave detectors.
ABSTRACT
Several stars detected moving at velocities near to or exceeding the Galactic escape speed likely originated in the Milky Way disc. We quantitatively explore the ‘binary supernova scenario’ ...hypothesis, wherein these ‘hyper-runaway’ stars are ejected at large peculiar velocities when their close, massive binary companions undergo a core-collapse supernova and the binary is disrupted. We perform an extensive suite of binary population synthesis simulations evolving massive systems to determine the assumptions and parameters that most impact the ejection rate of fast stars. In a simulation tailored to eject fast stars, we find the most likely hyper-runaway star progenitor binary is composed of a massive (${\sim}30\, \mathrm{ M}_{\odot }$) primary and an ${\sim}3\!-\!4\, \mathrm{ M}_{\odot }$ companion on an orbital period that shrinks to ≲1 d prior to the core collapse following a common-envelope phase. The black hole remnant formed from the primary must receive a natal kick ≳1000 km s−1 to disrupt the binary and eject the companion at a large velocity. We compare the fast stars produced in these simulations to a contemporary census of early-type Milky Way hyper-runaway star candidates. We find that these rare objects may be produced in sufficient number only when poorly constrained binary evolution parameters related to the strength of post-core-collapse remnant natal kicks and common-envelope efficiency are adjusted to values currently unsupported – but not excluded – by the literature. We discuss observational implications that may constrain the existence of these putative progenitor systems.
Present and upcoming time-domain astronomy efforts, in part driven by gravitational-wave follow-up campaigns, will unveil a variety of rare explosive transients in the sky. Here, we focus on ...pulsational pair-instability evolution, which can result in signatures that are observable with electromagnetic and gravitational waves. We simulated grids of bare helium stars to characterize the resulting black hole (BH) masses together with the ejecta composition, velocity, and thermal state. We find that the stars do not react “elastically” to the thermonuclear ignition in the core: there is not a one-to-one correspondence between pair-instability driven ignition and mass ejections, which causes ambiguity as to what is an observable pulse. In agreement with previous studies, we find that for initial helium core masses of 37.5
M
⊙
≲
M
He, init
≲ 41
M
⊙
, corresponding to carbon-oxygen core masses 27.5
M
⊙
≲
M
CO
≲ 30.1
M
⊙
, the explosions are not strong enough to affect the surface. With increasing initial helium core mass, they become progressively stronger causing first large radial expansion (41
M
⊙
≲
M
He, init
≲ 42
M
⊙
, corresponding to 30.1
M
⊙
≲
M
CO
≲ 30.8
M
⊙
) and, finally, also mass ejection episodes (for
M
He, init
≳ 42
M
⊙
, or
M
CO
≳ 30.8
M
⊙
). The lowest mass helium core to be fully disrupted in a pair-instability supernova is
M
He, init
≃ 80
M
⊙
, corresponding to
M
CO
≃ 55
M
⊙
. Models with
M
He, init
≳ 200
M
⊙
(
M
CO
≳ 114
M
⊙
) reach the photodisintegration regime, resulting in BHs with masses of
M
BH
≳ 125
M
⊙
. Although this is currently considered unlikely, if BHs from these models form via (weak) explosions, the previously-ejected material might be hit by the blast wave and convert kinetic energy into observable electromagnetic radiation. We characterize the hydrogen-free circumstellar material from the pulsational pair-instability of helium cores by simply assuming that the ejecta maintain a constant velocity after ejection. We find that our models produce helium-rich ejecta with mass of 10
−3
M
⊙
≲
M
CSM
≲ 40
M
⊙
, the larger values corresponding to the more massive progenitor stars. These ejecta are typically launched at a few thousand km s
−1
and reach distances of ∼10
12
− 10
15
cm before the core-collapse of the star. The delays between mass ejection events and the final collapse span a wide and mass-dependent range (from subhour to 10
4
years), and the shells ejected can also collide with each other, powering supernova impostor events before the final core-collapse. The range of properties we find suggests a possible connection with (some) type Ibn supernovae.
PDF
