Periodic Reporting for period 1 - TransPIre (Transients Illuminating the Fates of the Most Massive Stars)
Période du rapport: 2023-01-01 au 2025-06-30
The TransPIre project seeks to understand the final fates of the most massive stars in the Universe. The evolution and end fate of such stars are important for many different areas of astrophysics, ranging from understanding the very first stars and galaxies, the formation of heavy elements and galaxy enrichment, the physics of supernova explosions, and the formation of compact objects like neutron stars and black holes.
Since the 1960s, it has been hypothesised that the most massive stars -- those whose helium cores exceed about 35 solar masses -- will evolve in a fundamentally different way than their less massive counterparts, because the core temperatures get high enough for spontaneous electron-positron production. This in turn momentarily softens the equation of state, removing pressure support in the stellar core and leads to an instability that can either give rise to a series of pulsations and mass ejections before the star ends in a core-collapse, or, in the most massive regime, lead to the runaway thermonuclear explosion of the entire stellar core, a so-called pair-instability supernova. In the latter case, there is no compact remnant left behind. With the discovery of black holes in the pair-instability mass range by gravitational wave experiments like LIGO/Virgo, as well as the focus on the first stars and galaxies with the successful launch of James Webb Space Telescope, it is crucial to understand this regime in stellar evolution in order to be able to interpret the results.
At the same time, new experiments in time-domain astronomy are coming online, such as the LSST project at the Vera Rubin Observatory in 2025. Its combination of area, depth and cadence gives unprecedented survey volumes allowing for the detection of rare events, and in particular, predictions from stellar evolution modeling tuned to explain the black hole population seen by LIGO/Virgo suggests that there should be pair-instability supernovae present in the LSST data stream. This project aims to exploit this opening of parameter space to search for transients related to the pair-instability phenomenon -- both full-blown pair-instability supernovae, and those resulting from pulsational pair-instability mass loss.
Since the 1960s, it has been hypothesised that the most massive stars -- those whose helium cores exceed about 35 solar masses -- will evolve in a fundamentally different way than their less massive counterparts, because the core temperatures get high enough for spontaneous electron-positron production. This in turn momentarily softens the equation of state, removing pressure support in the stellar core and leads to an instability that can either give rise to a series of pulsations and mass ejections before the star ends in a core-collapse, or, in the most massive regime, lead to the runaway thermonuclear explosion of the entire stellar core, a so-called pair-instability supernova. In the latter case, there is no compact remnant left behind. With the discovery of black holes in the pair-instability mass range by gravitational wave experiments like LIGO/Virgo, as well as the focus on the first stars and galaxies with the successful launch of James Webb Space Telescope, it is crucial to understand this regime in stellar evolution in order to be able to interpret the results.
At the same time, new experiments in time-domain astronomy are coming online, such as the LSST project at the Vera Rubin Observatory in 2025. Its combination of area, depth and cadence gives unprecedented survey volumes allowing for the detection of rare events, and in particular, predictions from stellar evolution modeling tuned to explain the black hole population seen by LIGO/Virgo suggests that there should be pair-instability supernovae present in the LSST data stream. This project aims to exploit this opening of parameter space to search for transients related to the pair-instability phenomenon -- both full-blown pair-instability supernovae, and those resulting from pulsational pair-instability mass loss.
In the first two years of the project, we have made substantial progress in the study of luminous, interacting supernovae, including those that are candidates for the pulsational pair-instability mechanism, i.e. that are consistent with having very massive progenitors and eruptive mass-loss. This work is also important for building machine-learning tools for searching for pair-instability supernovae, since luminous, interacting supernovae occupy a similar part of parameter space and have been missing from previous training sets, and are in themselves candidates for pulsational pair-instability supernovae. We have:
- Compiled and published the first sample study of hydrogen-rich superluminous supernovae, the most extreme transients powered by circumstellar interaction.
- Performed the first systematic search for superluminous supernovae with eruptive mass loss through a novel absorption spectroscopy technique. Prior to this work, only two examples were known, and both discovered serendipitously. Our search has uncovered three more examples, consistent with a large mass eruption in the final year before the star exploded. The modeling techniques developed can also be used to put constraints from the spectra where the mass loss signature is not seen.
- Carried out and published several single-object analyses of interacting supernovae, as well as those with signs of an eruption close to the time of explosion.
Moving forward, we are focusing on improving our search tools to be deployed on the LSST data stream, and expect to be following up the best candidates live.
- Compiled and published the first sample study of hydrogen-rich superluminous supernovae, the most extreme transients powered by circumstellar interaction.
- Performed the first systematic search for superluminous supernovae with eruptive mass loss through a novel absorption spectroscopy technique. Prior to this work, only two examples were known, and both discovered serendipitously. Our search has uncovered three more examples, consistent with a large mass eruption in the final year before the star exploded. The modeling techniques developed can also be used to put constraints from the spectra where the mass loss signature is not seen.
- Carried out and published several single-object analyses of interacting supernovae, as well as those with signs of an eruption close to the time of explosion.
Moving forward, we are focusing on improving our search tools to be deployed on the LSST data stream, and expect to be following up the best candidates live.
Before this project, only a handful of single-object analysis of luminous, interacting supernovae existed, and they had never been studied systematically as a class before. Our work both provides insight into the extremes of mass loss and interaction in supernovae, and provides a large sample of light curves that can be used in future training sets for supernova identification and classification.
We are currently working on incorporating these results into our machine-learning based classification and alert filtering tools. Once LSST comes online later in 2025, we will be using these tools to search for, and follow up, candidates for the most massive stellar explosions.
We are currently working on incorporating these results into our machine-learning based classification and alert filtering tools. Once LSST comes online later in 2025, we will be using these tools to search for, and follow up, candidates for the most massive stellar explosions.