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Register a new userPredictions for the hydrogen-free ejecta of pulsational pair-instability supernovae
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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 agreement with previous studies, we find that for carbon-oxygen core masses 28Msun< M_CO<30.5Msun the explosions are not strong enough to affect the surface. With increasing mass, they first cause large radial expansion (30.5Msun<M_CO<31.4Msun), and finally, also mass ejection episodes (M_CO>31.4Msun). The lowest mass to be fully disrupted in a pair-instability supernova is M_CO=57Msun. Models with M_CO>121Msun reach the photodisintegration regime, resulting in BHs with M_BH>125Msun. If the pulsating models produce BHs via (weak) explosions, the previously-ejected material might be hit by the blast wave. We characterize the H-free circumstellar material from the pulsational pair-instability of helium cores assuming simply that the ejecta maintain a constant velocity after ejection. Our models produce He-rich ejecta with mass 10^{-3}Msun<M_CSM<40Msun. These ejecta are typically launched at a few thousand kms and reach distances of ~10^{12}-10^{15} cm before core-collapse. The delays between mass ejection events and the final collapse span a wide and mass-dependent range (from sub-hour to 10^4 years), and the shells ejected can also collide with each other. The range of properties we find suggests a possible connection with (some) type Ibn supernovae.
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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 collisions, we show that the development of a Rayleigh-Taylor instability truncates the growth of the high density spike and drives mixing between the shells. The progenitor is a 110 Msun solar-metallicity star that was shown in earlier work to produce a superluminous supernova. The light curve of this more realistic model has a peak luminosity and duration that are similar to those of 1D models but a structure that is smoother.
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 aspects to determine the subsequent observational characteristics of the explosion. We examine the dynamics of a sample of stellar models and rotation rates and discuss the implications for the first stars, for LBV-like phenomena, and for superluminous supernovae. We find that the shells ejected by pulsational pair-instability events with rapidly rotating progenitors (>30% the critical value) are hydrogen-poor and helium and oxygen-rich.
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 ($Z_odot/10$) single helium stars using the texttt{MESA} software instrument. For PPISN progenitors with pre-pulse masses $>50M_odot$ we find that, after a pulse, heat deposited throughout the layers of the star that remain bound cause it to expand to more than $100R_odot$ for periods of $10^2-10^4;$~yrs depending on the mass of the progenitor. This results in long-lived phases of Roche-lobe overflow or even common-envelope events if there is a close binary companion, leading to additional electromagnetic transients associated to PPISN eruptions. If we ignore the effect of these interactions, we find that mass loss from PPISNe reduces the final black hole spin by $sim 30%$, induces eccentricities below the threshold of detectability of the LISA observatory, and can produce a double-peaked distribution of measured chirp masses in BBH mergers observed by ground-based detectors.
We calculate the evolution of massive stars, which undergo pulsational pair-instability (PPI) when the O-rich core is formed. The evolution from the main-sequence through the onset of PPI is calculated for stars with the initial masses of $80 - 140$ $M_{odot}$ and metallicities of $Z = 10^{-3} - 1.0$ $Z_odot$. Because of mass loss, $Z leq 0.5$ $Z_odot$ is necessary for stars to form He cores massive enough (i.e., mass $>40 ~M_odot$) to undergo PPI. The hydrodynamical phase of evolution from PPI through the beginning of Fe core collapse is calculated for the He cores with masses of $40 - 62 ~M_odot$ and $Z = 0$. During PPI, electron-positron pair production causes a rapid contraction of the O-rich core which triggers explosive O-burning and a pulsation of the core. We study the mass dependence of the pulsation dynamics, thermodynamics, and nucleosynthesis. The pulsations are stronger for more massive He cores and result in such a large amount of mass ejection such as $3 - 13$ $M_odot$ for $40 - 62 ~M_odot$ He cores. These He cores eventually undergo Fe-core collapse. The $64 ~M_odot$ He core undergoes complete disruption and becomes a pair-instability supernova. The H-free circumstellar matter ejected around these He cores is massive enough for to explain the observed light curve of Type I (H-free) superluminous supernovae with circumstellar interaction. We also note that the mass ejection sets the maximum mass of black holes (BHs) to be $sim 50$ $M_{odot}$, which is consistent with the masses of BHs recently detected by VIRGO and aLIGO.
Massive stars of helium cores of 35-65 Msun eventually encounter the electron/positron creation instability, and it triggers explosive carbon or oxygen burning that produces several thermonuclear eruptions. The resulting catastrophe collisions of eruptive shells sometimes produce luminous transients with peak luminosity of $10^{43} - 10^{44}$ erg/sec, known as pulsational pair-instability supernovae (PPISNe). Previous 2D simulations of colliding shells show the development of Rayleigh-Taylor (RT) instabilities and mixing. Here we present radiation hydrodynamic PPISNe simulations of a 110 Msun solar-metallicity star that was promising to produce a superluminous transit in the early work. Our comprehensive study contains a suite of one-, two-, and three-dimensional models. We discuss the impact of dimensionality and fluid instabilities on the resulting light curves. The results show the RT mixing found in previous multidimensional hydro studies transforms into a thin and distorted shell due to radiative cooling. Radiation from the wiggly shell peaks at its bolometric light curve of $sim 2times10^{43}$ erg/sec, lasting about 150 days and following with a plateau of $sim 3times10^{42}$ erg/sec for another two hundred days before it fades away. The total radiation energy emitted from colliding shells is $sim 1.8 times 10^{50}$ erg, which is $sim 27%$ of the kinetic energy of the major eruption. The dimensional effects also manifest on the physical properties, such as irregularity and thickness of the shell. Our study suggests PPISNe is a promising candidate of luminous SNe, the radiation of which originates from colliding shells with a homogeneous mixing of ejecta.
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