Pulsational pair instability as an explanation for the most luminous supernovae

Abstract: The extremely luminous supernova SN 2006gy challenges the traditional view that the collapse of a stellar core is the only mechanism by which a massive star makes a supernova, because it seems too luminous by more than a factor of ten. Here we report that the brightest supernovae in the modern Universe arise from collisions between shells of matter ejected by massive stars that undergo an interior instability arising from the production of electron-positron pairs. This "pair instability" leads to explosive burning that is insufficient to unbind the star, but ejects many solar masses of the envelope. After the first explosion, the remaining core contracts and searches for a stable burning state. When the next explosion occurs, several solar masses of material are again ejected, which collide with the earlier ejecta. This collision can radiate 1E50 erg of light, about a factor of ten more than an ordinary supernova. Our model is in good agreement with the observed light curve for SN 2006gy and also shows that some massive stars can produce more than one supernova-like outburst.

• The paper shows that pulsational pair instability causes repeated mass ejections in massive stars (95-130 M☉), leading to supernovae with luminosities far exceeding typical type-II events.
• Advanced computational models like Kepler and Stella were used to simulate light curves that closely match observations of SN 2006gy.
• The findings suggest that PPI can trigger multiple supernova-like outbursts, challenging traditional core-collapse models and opening new avenues for astrophysical research.

Pulsational Pair Instability as an Explanation for the Most Luminous Supernovae: A Detailed Analysis

This paper explores an advanced theoretical model explaining the phenomena underlying extremely luminous supernovae, particularly focusing on SN 2006gy. Conventionally, the luminosity of supernovae has been attributed chiefly to the collapse of a stellar core. However, this paper challenges this paradigm by introducing the concept of pulsational pair instability (PPI) as a significant factor potentially causing supernovae of high luminosity surpassing that of typical type-II supernovae by an order of magnitude. The authors argue that the PPI mechanism involves the formation of electron-positron pairs, leading to pulsational thermonuclear eruptions that fail to completely unbind the star but sufficiently disrupt its outer layers.

Pulsational Pair Instability Supernovae (PPISN): Mechanism and Implications

The authors provide substantial evidence that stars within certain mass ranges (95-130 solar masses) may undergo this PPI, characterized by repeated pulsational ejections which result in collisions of massive expelled material. These interactions are responsible for the intense radiative output observed. The process starts with the conversion of thermal energy into rest mass energy of electron-positron pairs during the late stages of stellar evolution. This conversion induces contraction and subsequent explosive nuclear burning, ejecting several solar masses of the star’s envelope. The remnants continue to contract and may undergo multiple cycles of instability, ejecting more material in each event.

Mathematical and Computational Modeling

The paper uses rigorous computational models, notably the Kepler and Stella codes, to calculate the evolution of a 110-solar-mass star that eventually produces a helium core conducive to pulsational pair instability. The computational findings illustrate significant light curve outputs mimicking observed characteristics of SN 2006gy. The Stella radiation-hydrodynamics code simulates multi-wavelength light curves and interaction dynamics, correlating with real observational data, thus supporting their hypothesis about PPI as a realistic scenario for producing such luminous events. The emission is primarily in near-optical bands due to the nature of the shell collisions and resulting energy release.

Observational Consequences and Challenges

The implications of these findings are profound, both for understanding past and predicting future observations. The model implies that pair-instability mechanisms can generate varied light curve signatures, ranging from supernova impostors to brilliant radiative outputs, depending largely on initial stellar mass and mass loss history. It suggests that some massive stars might experience more than one supernova-like outburst due to successive PPI events – a concept that challenges conventional understanding of supernovae lifecycle.

The authors critically compare these theoretical implications with alternative models – such as traditional pair-instability supernovae requiring significant amounts of Nickel (Ni) for radiative luminosity. Such models may struggle to explain the compact light curve of SN 2006gy without invoking exceptionally massive progenitors or unrealistic assumptions about ejected masses.

Future Directions and Implications

The model's implications extend to astrophysical phenomena such as gamma-ray bursts and supernova impostors. The study opens avenues for exploration into rotational effects, magnetic fields, and initial mass distribution conditions influencing the final stages of stellar evolution. The potential observation of repeated supernova-like events in certain stellar remnants also poses an intriguing question, warranting more detailed temporal astronomical observations.

In conclusion, the pulsational pair instability paradigm provides a robust mechanism for the explanation of extremely luminous supernovae, potentially reshaping understanding in stellar astrophysics. Future studies are encouraged to further refine these models and address unresolved questions about the mass loss rates and chemical compositions required to enable such extraordinary stellar finales.