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Register a new userMass ejection by pulsational pair instability in very massive stars and implications for luminous supernovae
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Massive stars having a CO core of $sim$40-60 M$_odot$ experience pulsational pair-instability (PPI) after carbon-burning. This instability induces strong pulsations of the whole star and a part of outer envelope is ejected. We investigate the evolution and mass ejection of metal-poor very massive stars which experience PPI. We use stellar models with initial masses of 140, 200, and 250 M$_odot$ and the metallicity Z=0.004. Their masses decrease to 54.09, 58.65, and 61.03 M$_odot$ before the neon-burning owing to mass-loss and He mass fraction at the surface becomes about 20%. During the PPI period of $sim$1-2000 yr, they experience six, four, and three pulsations, respectively. The larger CO-core model has the longer PPI period and ejects the larger amount of mass. Since almost all surface He has been lost by the pulsations, these stars become Type Ic supernovae if they explode. Light curves during the PPI stage and supernovae are investigated and are implicated in luminous supernovae. The luminosity created by the interaction of different PPI ejecta becomes $M_{rm bol} sim -16$ to $-20$. The interaction between the circumstellar shell ejected by PPI and the supernova ejecta can be more luminous. These luminous transients could be an origin of Type I superluminous supernovae and supernovae with precursor.
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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.
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.
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.
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.
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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