Numerical studies of primordial star formation suggest that the first stars in the universe may have been very massive. Stellar models indicate that non-rotating Population III stars with initial masses of 140-260 Msun die as highly energetic pair-instability supernovae. We present new two-dimensional simulations of primordial pair-instability supernovae done with the CASTRO code. Our simulations begin at earlier times than previous multidimensional models, at the onset of core collapse, to capture any dynamical instabilities that may be seeded by collapse and explosive burning. Such instabilities could enhance explosive yields by mixing hot ash with fuel, thereby accelerating nuclear burning, and affect the spectra of the supernova by dredging up heavy elements from greater depths in the star at early times. Our grid of models includes both blue supergiants and red supergiants over the range in progenitor mass expected for these events. We find that fluid instabilities driven by oxygen and helium burning arise at the upper and lower boundaries of the oxygen shell $\sim$ 20 - 100 seconds after core bounce. Instabilities driven by burning freeze out after the SN shock exits the helium core. As the shock later propagates through the hydrogen envelope, a strong reverse shock forms that drives the growth of Rayleigh--Taylor instabilities. In red supergiant progenitors, the amplitudes of these instabilities are sufficient to mix the supernova ejecta.
Pristine stars with masses between ~140 and 260 M_sun are theoretically predicted to die as pair-instability supernovae. These very massive progenitors could come from Pop III stars in the early universe. We model the light curves and spectra of pair-instability supernovae over a range of masses and envelope structures. At redshifts of reionization z >= 6, we calculate the rates and detectability of pair-instability and core collapse supernovae, and show that with the James Webb Space Telescope, it is possible to determine the contribution of Pop III and Pop II stars toward reionization by con…
We present 2D simulations of pair-instability supernovae considering rapid rotation during their explosion phases. Recent studies of the Pop III star formation suggested that these stars could be born with a mass scale about 100 Msun and with a strong rotation. Based on stellar evolution models, these massive Pop III stars might have died as highly energetic pair-instability supernovae. We perform 2D calculations to investigate the impact of rotation on pair-instability supernovae. Our results suggest that rotation leads to an aspherical explosion due to an anisotropic collapse. If the first s…
Observed supermassive black holes in the early universe have several proposed formation channels, in part because most of these channels are difficult to probe. One of the more promising channels, the direct collapse of a supermassive star, has several possible probes including the explosion of a helium-core supermassive star triggered by a general relativistic instability. We develop a straightforward method for evaluating the general relativistic radial instability without simplifying assumptions and apply it to population III supermassive stars taken from a post Newtonian stellar evolution …
The observational signatures of the first cosmic explosions and their chemical imprint on second-generation stars both crucially depend on how heavy elements mix within the star at the earliest stages of the blast. We present numerical simulations of the early evolution of Population III pair-instability supernovae with the new adaptive mesh refinement code CASTRO. In stark contrast to 15 - 40 Msun core-collapse primordial supernovae, we find no mixing in most 150 - 250 Msun pair-instability supernovae out to times well after breakout from the surface of the star. This may be the key to determ…
Massive stars that end their lives with helium cores in the range of 35 to 65 Msun are known to produce repeated thermonuclear outbursts due to a recurring pair-instability. In some of these events, solar masses of material are ejected in repeated outbursts of several times 10$^{50}$ erg each. Collisions between these shells can sometimes produce very luminous transients that are visible from the edge of the observable universe. Previous 1D studies of these events produce thin, high-density shells as one ejection plows into another. Here, in the first multidimensional simulations of these coll…
In this Letter, we report the outcomes of 1-D modelling of a rotating 25 M$_{\odot}$ zero-age main-sequence Population III star up to the stage of the onset of core collapse. Rapidly rotating models display violent and sporadic mass losses after the Main-Sequence stage. In comparison to the solar metallicity model, Pop III models show very small pre-supernova radii. Further, with models at the stage of the onset of core collapse, we simulate the hydrodynamic simulations of resulting supernovae. Depending upon the mass losses due to corresponding rotations and stellar winds, the resulting super…
Interactions between massive stars in binaries are thought to be responsible for much of the observed diversity of supernovae. As surveys probe rarer populations of events, we should expect to see supernovae arising from increasingly uncommon progenitor channels. Here we examine a scenario in which massive stars merge after they have both formed a hydrogen-exhausted core. We suggest this could produce stars which explode as pair-instability supernovae (PISNe) with significantly more hydrogen, at a given metallicity, than in single-star models with the same pre-explosion oxygen-rich core mass. …
ULTIMATE-Subaru (Ultra-wide Laser Tomographic Imager and MOS with AO for Transcendent Exploration on Subaru) and WFIRST (Wide Field Infra-Red Survey Telescope) are the next generation near-infrared instruments that have a large field-of-view. They allow us to conduct deep and wide transient surveys in near-infrared. Such a near-infrared transient survey enables us to find very distant supernovae that are redshifted to the near-infrared wavelengths. We have performed the mock transient surveys with ULTIMATE-Subaru and WFIRST to investigate their ability to discover Population III pair-instabili…
We present preliminary results from two dimensional numerical studies of pair instability supernova (PSN). We study nuclear burning, hydrodynamic instabilities and explosion of very massive stars. Use a new radiation-hydrodynamics code, CASTRO.
The final evolution of stars in the mass range 70 - 140 solar masses is explored. Depending upon their mass loss history and rotation rates, these stars will end their lives as pulsational pair-instability supernovae producing a great variety of observational transients with total durations ranging from weeks to millennia and luminosities from 10$^{41}$ to over 10$^{44}$ erg s$^{-1}$. No non-rotating model radiates more than $5 \times 10^{50}$ erg of light or has a kinetic energy exceeding $5 \times 10^{51}$ erg, but greater energies are possible, in principle, in magnetar-powered explosions w…
We investigated the impacts of magnetorotational instability (MRI) on the dynamics of weakly magnetized, rapidly rotating core-collapse by conducting high resolution MHD simulations in axisymmetry with simplified neutrino transfer. We found that an initially sub-magnetar class magnetic field is drastically amplified by MRI and substantially affects the dynamics thereafter. Although the magnetic pressure is not strong enough to eject matter, the amplified magnetic field efficiently transfers angular momentum from higher to lower latitudes, which causes the expansion of the heating region at low…
Population III stars that die as pair-instability supernovae are usually thought to fall in the mass range of 140 - 260 M$_{\odot}$. But several lines of work have now shown that rotation can build up the He cores needed to encounter the pair instability at stellar masses as low as 90 $_{\odot}$. Depending on the slope of the initial mass function of Population III stars, there could be 4 - 5 times as many stars from 90 - 140 $_{\odot}$ in the primordial universe than in the usually accepted range. We present numerical simulations of the pair-instability explosions of such stars performed with…
In certain mass ranges, massive stars can undergo a violent pulsation triggered by the electron/positron pair instability that ejects matter, but does not totally disrupt the star. After one or more of these pulsations, such stars are expected to undergo core-collapse to trigger a supernova explosion. The mass range susceptible to this pulsational phenomena may be as low as 50-70 Msun if the progenitor is of very low metallicity and rotating sufficiently rapidly to undergo nearly homogeneous evolution. The mass, dynamics, and composition of the matter ejected in the pulsation are important asp…
It was recently proposed that exotic particles can trigger a new stellar instability which is analogous to the e-e+ pair instability if they are produced and reach equilibrium in the stellar plasma. In this study, we construct axion instability supernova (AISN) models caused by the new instability to predict their observational signatures. We focus on heavy axion-like particles (ALPs) with masses of ~400 keV--2 MeV and coupling with photons of g_{ag}~10^{-5} GeV^{-1}. It is found that the 56Ni mass and the explosion energy are significantly increased by ALPs for a fixed stellar mass. As a resu…
Galaxy clusters contain much more metal per star, typically 3 times as much, than is produced in normal galaxies. We set out to determine what changes are needed to the stellar mass function and supernovae rates to account for this excess metal. In particular, we vary the Type Ia supernovae rate, IMF slope, upper and lower mass cutoffs, and the merger rate of massive stars. We then use existing simulation results for metal production from AGB stars, Type Ia SNe and core-collapse SNe to calculate the total amount of each element produced per solar mass of star formation. For models with very ma…
We discuss the relevance of the magnetorotational instability (MRI) in core-collapse supernovae (CCSNe). Our recent numerical studies show that in CCSNe, the MRI is terminated by parasitic instabilities of the Kelvin-Helmholtz type. To determine whether the MRI can amplify initially weak magnetic fields to dynamically relevant strengths in CCSNe, we performed three-dimensional simulations of a region close to the surface of a differentially rotating proto-neutron star in non-ideal magnetohydrodynamics with two different numerical codes. We find that under the conditions prevailing in proto-neu…
Super-luminous supernovae that radiate more than 10^44 ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of 'pair-instability' supernovae. Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-30 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of 56Ni are synthesized; this isotope decays to…
Pair Instability Supernovae have been suggested as candidates for some Super Luminous Supernovae, such as SN 2007bi, and as one of the dominant types of explosion occurring in the early Universe from massive, zero-metallicity Population III stars. The progenitors of such events can be rapidly rotating, therefore exhibiting different evolutionary properties due to the effects of rotationally-induced mixing and mass-loss. Proper identification of such events requires rigorous radiation hydrodynamics and radiative transfer calculations that capture not only the behavior of the light curve but als…
Superluminous supernovae have been proposed to arise from Population III progenitors that explode as pair-instability supernovae. Pop III stars are the first generation of stars in the Universe, and are thought to form as late as $z \sim 6$. Future near-infrared imaging facilities such as ULTIMATE-Subaru can potentially detect and identify these PISNe with a dedicated survey. Gravitational lensing by intervening structure in the Universe can aid in the detection of these rare objects by magnifying the high-$z$ source population into detectability. We perform a mock survey with ULTIMATE-Subaru,…
We investigated r-process nucleosynthesis in magneto-rotational supernovae, based on a new explosion mechanism induced by the magneto-rotational instability. A series of axisymmetric magneto-hydrodynamical simulations with detailed microphysics including neutrino heating is performed, numerically resolving the magneto-rotational instability. Neutrino-heating dominated explosions, enhanced by magnetic fields, showed mildly neutron-rich ejecta producing nuclei up to $A \sim 130$ (i.e. the weak r-process), while explosion models with stronger magnetic fields reproduce a solar-like r-process patte…
Stars with helium cores between ~64 and 133 M_sun are theoretically predicted to die as pair-instability supernovae. This requires very massive progenitors, which are theoretically prohibited for Pop II/I stars within the Galactic stellar mass limit due to mass loss via line-driven winds. However, the runaway collision of stars in a dense, young star cluster could create a merged star with sufficient mass to end its life as a pair-instability supernova, even with enhanced mass loss at non-zero metallicity. We show that the predicted rate from this mechanism is consistent with the inferred volu…
Context. Pulsational pair-instabilitye supernovae (PPISNe) and pair instability supernovae (PISNe) are the result of a thermonuclear runaway in the presence of a background electron-positron pair plasma. As such, their evolution and resultant black hole (BH) masses could possibly be affected by screening corrections due to the electron pair plasma. Aims. Sensitivity of PISNe and PPISNe to relativistic weak screening has been explored. Methods. In this paper a weak screening model that includes effects from relativistic pair production has been developed and applied at temperatures approaching …
We show that a self-interacting neutrino gas can spontaneously acquire a non-stationary pulsating component in its flavor content, with a frequency that can exactly cancel the "multi-angle" refractive effects of dense matter. This can then enable homogeneous and inhomogeneous flavor conversion instabilities to exist even at large neutrino and matter densities, where the system would have been stable if the evolution were strictly stationary. Large flavor conversions, especially close to a supernova core, are possible via this novel mechanism. This may have important consequences for the explos…
The discovery of 150 - 300 M$_{\odot}$ stars in the Local Group and pair-instability supernova candidates at low redshifts has excited interest in this exotic explosion mechanism. Realistic light curves for pair-instability supernovae at near-solar metallicities are key to identifying and properly interpreting these events as more are found. We have modeled pair-instability supernovae of 150 - 500 M$_{\odot}$ Z $\sim$ 0.1 - 0.4 Z$_{\odot}$ stars. These stars lose up to 80% of their mass to strong line-driven winds and explode as bare He cores. We find that their light curves and spectra are qu…
We present preliminary results from multidimensional numerical studies of pair instability supernova (PSN), studying the fluid instabilities that occur in multiple spatial dimensions. We use the new radiation-hydrodynamics code, CASTRO, and introduce a new mapping procedure that defines the initial conditions for the multidimensional runs in such a way that conservation of physical quantities is guaranteed at any level of resolution.
We consider the synchrotron emission from high energy electrons accelerated in supernova explosions of massive Population III stars in high redshift minihaloes of mass $10^{5\hbox {--}7} \rm M_\odot$. We show the resulting intensity of radio background from this process can be substantial, which could potentially explain the recently reported EDGES result, if not for the associated heating of the IGM by CR protons which are also produced at the same time. The trade-off between the radio background and heating is such that the 21 cm brightness temperature cannot be larger than $\vert ΔT_{21}\ve…
Observational evidence suggests that some very massive stars in the local Universe may die as pair-instability supernovae. We present 2D simulations of the pair-instability supernova of a non-zero metallicity star. We find that very little mixing occurs in this explosion because metals in the stellar envelope drive strong winds that strip the hydrogen envelope from the star prior to death. Consequently, a reverse shock cannot form and trigger fluid instabilities during the supernova. Only weak mixing driven by nuclear burning occurs in the earliest stages of the supernova, and it is too weak t…
New particles coupled to the Standard Model can equilibrate in stellar cores if they are sufficiently heavy and strongly coupled. In this work, we investigate the astrophysical consequences of such a scenario for massive stars by incorporating new contributions to the equation of state into a state of the art stellar structure code. We focus on axions in the "cosmological triangle", a region of parameter space with $300{\rm\,keV} \lesssim m_a \lesssim 2$ MeV, $g_{aγγ}\sim 10^{-5}$ GeV$^{-1}$ that is not presently excluded by other considerations. We find that for axion masses $m_a \sim m_e $, …
An increasing number of so-called superluminous supernovae (SLSNe) are discovered. It is believed that at least some of them with slowly fading light curves originate in stellar explosions induced by the pair instability mechanism. Recent stellar evolution models naturally predict pair instability supernovae (PISNe) from very massive stars at wide range of metallicities (up to Z=0.006, Yusof et al. 2013). In the scope of this study we analyse whether PISN models can match the observational properties of SLSNe with various light curve shapes. Specifically, we explore the influence of different …
The gravitational instability, responsible for the formation of the structure of the Universe, occurs below energy thresholds and above spatial scales of a self-gravitating expanding region, when thermal energy can no longer counterbalance self-gravity. I argue that at sufficiently-large scales, dark energy may restore thermal stability. This stability re-entrance of an isothermal sphere defines a turnaround radius, which dictates the maximum allowed size of any structure generated by gravitational instability. On the opposite limit of high energies and small scales, I will show that an ideal,…
Theoretical models predict that some of the first stars ended their lives as extremely energetic pair-instability supernovae (PISNe). With energies approaching 10^53 ergs, these supernovae are expected to be within the detection limits of the upcoming James Webb Space telescope (JWST), allowing observational constraints to be placed on the properties of the first stars. We estimate the source density of PISNe using a semi-analytic halo mass function based approach, accounting for the effects of feedback from star formation on the PISN rates using cosmological simulations. We estimate an upper …
Understanding the link between massive ($\gtrsim 30$ M$_{\odot{}}$) stellar black holes (BHs) and their progenitor stars is a crucial step to interpret observations of gravitational-wave events. In this paper, we discuss the final fate of very massive stars (VMSs), with zero-age main sequence (ZAMS) mass $>150$ M$_{\odot}$, accounting for pulsational pair-instability supernovae (PPISNe) and for pair-instability supernovae (PISNe). We describe an updated version of our population synthesis code SEVN, in which we added stellar evolution tracks for VMSs with ZAMS mass up to $350 $M$_{\odot{}}$ an…
Synchrotron emission from a supernova necessitates a magnetic field, but it is unknown how strong the relevant magnetic fields are, and what mechanism generates them. In this study, we perform high-resolution numerical gas dynamics calculations to determine the growth of turbulence due to Rayleigh-Taylor instability, and the resulting kinetic energy in turbulent fluctuations, to infer the strength of magnetic fields amplified by this turbulence. We find that Rayleigh-Taylor instability can produce turbulent fluctuations strong enough to amplify magnetic fields to a few percent of equipartition…
We infer the expected detection number of pair instability supernovae (PISNe) during the operation of the Euclid space telescope based on binary population models. Our models reproduce the global maximum of the rate at the primary BH mass of $\sim 9-10$ $M_\odot$, and the overall gradient of the primary BH mass distribution in the binary BH merger rate consistent with recent observations. We consider different PISN conditions depending on the $^{12}$C$(α, γ)^{16}$O reaction rate. The fiducial and $3σ$ models adopt the standard and $3σ$-smaller reaction rate, respectively. Our fiducial model pr…
A very massive star with a carbon-oxygen core in the range of $64$ M$_{\odot}<M_{\mathrm{CO}}<133$ M$_{\odot}$ is expected to undergo a very different kind of explosion known as a pair instability supernova. Pair instability supernovae are candidates for superluminous supernovae due to the prodigious amounts of radioactive elements they create. While the basic mechanism for the explosion is understood, how a star reaches a state is not, thus observations of a nearby pair-instability supernova would allow us to test current models of stellar evolution at the extreme of stellar masses. Much will…
The magnetorotational instability (MRI) can be a powerful mechanism amplifying the magnetic field in core-collapse supernovae. Whether initially weak magnetic fields can be amplified by this instability to dynamically relevant strengths is still a matter of debate. One of the main uncertainties concerns the process that terminates the growth of the instability. Parasitic instabilities of both Kelvin-Helmholtz and tearing-mode type have been suggested to play a crucial role in this process, disrupting MRI channel flows and quenching magnetic field amplification. We perform two-dimensional and t…
Both recent observations and stellar evolution models suggest that pair-instability supernovae (PISNe) could occur in the local Universe, at metallicities below Z_Sun/3. Previous PISN models were mostly produced at very low metallicities in the context of the early Universe. We present new PISNe models at a metallicity of Z=0.001, which are relevant for the local Universe. We take the self-consistent stellar evolutionary models of pair-instability progenitors with initial masses of 150 and 250 solar masses at metallicity of Z=0.001 by Langer et al. (2007) and follow the evolution of these mode…
Very massive 140-260 Msun stars can die as highly-energetic pair-instability supernovae (PI SNe) with energies of up to 100 times those of core-collapse SNe that can completely destroy the star, leaving no compact remnant behind. These explosions can synthesize $0.1-30$ Msun of radioactive Ni56, which can cause them to rebrighten at later times when photons due to Ni56 decay diffuse out of the ejecta. However, heat from the decay of such large masses of Ni56 could also drive important dynamical effects deep in the ejecta that are capable of mixing elements and affecting the observational signa…
The most iron-deficient stars in the Milky Way provide important observational constraints on the nature of astrophysical objects that have enriched the primordial gas with heavy elements from which these stars were formed. Among them, the recently discovered iron-deficient star SMSS J031300.36-670839.3 shows a remarkable chemical composition with non-detection of iron ([Fe/H]$<-7.1$) and large enhancement of carbon and magnesium relative to calcium. We investigate the supernova yields of metal-free (Population III) stars to interpret the observed abundance pattern for this star. We report tha…
The era of the universe's first (Population III) stars is essentially unconstrained by observation. Ultra-luminous and massive stars from this time altered the chemistry of the cosmos, provided the radiative scaffolding to support the formation of the first protogalaxies, and facilitated the creation and growth of now-supermassive black holes. Unfortunately, because these stars lie literally at the edge of the observable universe, they will remain beyond the reach of even the next generation of telescopes such as the James Webb Space Telescope and the Thirty-Meter Telescope. In this paper, we …
Some ancient, dim, metal-poor stars may have formed in the ashes of the first supernovae (SNe). If their chemical abundances can be reconciled with the elemental yields of specific Population III (Pop III) explosions, they could reveal the properties of primordial stars. But multidimensional simulations of such explosions are required to predict their yields because dynamical instabilities can dredge material up from deep in the ejecta that would otherwise be predicted to fall back on to the central remnant and be lost in one-dimensional (1D) models. We have performed two-dimensional (2D) nume…
Mergers of two stellar origin black holes are a prime source of gravitational waves and are under intensive investigations. One crucial ingredient in their modeling has so far been neglected. Pair-instability pulsation supernovae with associated severe mass loss may suppress formation of massive black holes, decreasing black hole merger rates for the highest black hole masses. The mass loss associated with pair-instability pulsation supernovae limits the Population I/II stellar-origin black hole mass to 50 Msun, in tension with earlier predictions that the maximum black hole mass could be as h…
In a previously presented proof-of-principle study, we established a parametrized spherically symmetric explosion method (PUSH) that can reproduce many features of core-collapse supernovae for a wide range of pre-explosion models. The method is based on the neutrino-driven mechanism and follows collapse, bounce and explosion. There are two crucial aspects of our model for nucleosynthesis predictions. First, the mass cut and explosion energy emerge simultaneously from the simulation (determining, for each stellar model, the amount of Fe-group ejecta). Second, the interactions between neutrinos …
The explosion mechanism of core-collapse supernovae has not been fully understood yet but multi-dimensional fluid instabilities such as standing accretion shock instability (SASI) and convection are now believed to be crucial for shock revival. Another multi-dimensional effect that has been recently argued is the asymmetric structures in progenitors, which are induced by violent convections in silicon/oxygen layers that occur before the onset of collapse, as revealed by recent numerical simulations of the last stage of massive star evolutions. Furthermore, it has been also demonstrated numeric…
The issue of which stars may reach the conditions of electron/positron pair formation instability is of importance to understand the final evolution both of the first stars and of contemporary stars. The criterion to enter the pair instability regime in density and temperature is basically controlled by the mass of the oxygen core. The main sequence masses that produce a given oxygen core mass are, in turn, dependent on metallicity, mass loss, and convective and rotationally-induced mixing. We examine the evolution of massive stars to determine the minimum main sequence mass that can encounter…
Pair-instability and pulsational pair-instability supernovae (PPISN) 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 ($Z_\odot/10$) singl…
We show that the backreaction of left-handed neutrinos out of equilibrium on the matter sector induces an electric current proportional to a magnetic field even without a chiral imbalance for electrons in core-collapse supernovae. We derive the transport coefficient of this effect based on the recently formulated chiral radiation transport theory for neutrinos. This chiral electric current generates a strong magnetic field via the so-called chiral plasma instability, which could provide a new mechanism for the strong and stable magnetic field of magnetars. We also numerically study the physica…
We study the stability of disc accretion in the recurrent nova RS Ophiuchi. We construct a one-dimensional time-dependent model of the binary-disc system, which includes viscous heating and radiative cooling and a self-consistent treatment of the binary potential. We find that the extended accretion disc in this system is always unstable to the thermal-viscous instability, and undergoes repeated disc outbursts on ~10-20yr time-scales. This is similar to the recurrence time-scale of observed outbursts in the RS Oph system, but we show that the disc's accretion luminosity during outburst is insu…
Since the discovery of GW190521, several proposals have been put forward to explain the formation of a black hole in the mass gap caused by (pulsational) pair-instability, $M = 65-130 M_\odot$. We calculate the mass ejection of Pop III stars by the pulsational pair-instability (PPI) process using a stellar evolution and hydrodynamical code. If a relatively small, but reasonable value is adopted for the overshooting parameter, the stars do not become red super giants during the PPI phase. We show that in this case most of the hydrogen envelope remains after the mass ejection by PPI. We find tha…
Bearing in mind the application to core-collapse supernovae, we study nonlinear properties of the magneto-rotational instability (MRI) by means of three- dimensional simulations in the framework of a local shearing box approximation. By changing systematically the shear rates that symbolize the degree of differential rotation in nascent proto-neutron stars (PNSs), we derive a scaling relation between the turbulent stress sustained by the MRI and the shear- vorticity ratio. Our parametric survey shows a power-law scaling between the turbulent stress ($<< w_{\rm tot}>>$) and the shear- vorticity…
Pair-instability supernovae (PISNe) are the ultimate cosmic lighthouses, capable of being observed at z<25 and revealing the properties of primordial stars at cosmic dawn. But it is now understood that the spectra and light curves of these events evolved with redshift as the universe became polluted with heavy elements because chemically enriched stars in this mass range typically lose most of their hydrogen envelopes and explode as bare helium cores. The light curves of such transients can be considerably dimmer in the near infrared (NIR) today than those of primordial PISNe of equal energy a…
Present time-domain astronomy efforts will unveil a variety of rare transients. We focus here on pulsational pair-instability evolution, which can result in signatures observable with electromagnetic and gravitational waves. We simulate grids of bare helium stars to characterize the resulting black hole (BH) masses and ejecta composition, velocity, and thermal state. The stars do not react "elastically" to the thermonuclear explosion: there is not a one-to-one correspondence between pair-instability driven ignition and mass ejections, causing ambiguity in what is an observable pulse. In agreem…
For the initial mass range (140 < M < 260 Msun) stars die in a thermonuclear runaway triggered by the pair-production instability. The supernovae they make can be remarkably energetic (up to ~10^53 ergs) and synthesize considerable amounts of radioactive isotopes. Here we model the evolution, explosion, and observational signatures of representative pair-instability supernovae (PI SNe) spanning a range of initial masses and envelope structures. The predicted light curves last for hundreds of days and range in luminosity, from very dim to extremely bright, L ~ 10^44 ergs/s. The most massive eve…
So called superluminous supernovae have been recently discovered in the local Universe. It appears possible that some of them originate from stellar explosions induced by the pair instability mechanism. Recent stellar evolution models also predict pair instability supernovae (PISNe) from very massive stars at fairly high metallicities (i.e. Z~0.004). We provide supernova (SN) models and synthetic light curves for two progenitor models, a 150 Msun red-supergiant and a 250 Msun yellow-supergiant at a metallicity of Z=0.001, for which the evolution from the main sequence to collapse, and the init…
