Periodic Reporting for period 5 - SUPERSTARS (Type Ia supernovae: from explosions to cosmology)
Periodo di rendicontazione: 2023-09-01 al 2024-08-31
Type Ia supernovae are the luminous deaths of small incredibly dense stars called white dwarfs. They are the main producers of the element, iron, in the Universe that are produced during the hot dense explosions that mark the ends of their lives. They are also essential for understanding the make-up of our Universe and were instrumental in the discovery of dark energy. However, despite a number of decades of research, we still do not understand how exactly they explode. We are now in a position to make big leaps forward in our understanding through the advent of new state-of-the-art astrophysical transient surveys that are scanning the sky looking for new transients that have just exploded. Catching the explosions very early is crucial for solving the mystery of how they explode because subtle clues are present at this time. The aim of the project SUPERSTARS was to use data from these next-generation surveys, combined with the latest theoretical models, to understand the origin of Type Ia supernovae. This involved two distinct work packages, i) to build a legacy sample of Type Ia supernovae with the best data possible and ii) to explore the diversity of how the explode by observing the zoo of exotic transients that have recently begun to be detected in these surveys. Together these data will be used to constrain the explosion mechanisms and diversity of Type Ia supernovae, allowing us to understand the origin of elements such as iron in the Universe as well as improving the use of Type Ia supernovae as cosmological distance indicators in the Universe. The main conclusions of the action, include constraining for the first time in a meaningful sample the relative rates of white dwarf explosions in the Universe, as well as understanding the presence of circumstellar material around SNe Ia and the link to their explosion mechanisms.
One of the main results achieved from the project so far are an increased understanding of the very early times after the SN explosion both from an observational perspective and from a theoretical perspective. The other is the studies of the diversity of supernovae explosions that although we have found good model matches to all the new transients have suggested that circumstellar interaction may play a much more prominent role than previously thought.This project is split into two work packages (WP1 and WP2). WP1 focuses on producing a combined sample of multiple progenitor probes (early light curves, circumstellar material, late-time observations) for Type Ia supernovae. WP2 focuses on understanding exotic thermonuclear transients and comparing them to modelling predictions. The project made extensive use of data from the Zwicky Transient Facility (ZTF), as well as radiative transfer modelling, resulting in numerous publications - many of these are released as part of the ZTF Type Ia supernovae working group's Data Release 2 (DR2). These have resulted in new insights into the explosion mechanisms of normal Type Ia supernovae, including the occurrence rates of flux excesses in early light curves, the properties of their host galaxies and the presence of circumstellar material, as well as linking to detailed explosion models via radiative transfer and neural network modelling. The diversity of white-dwarf transients was also constrained including calculating relative rates of rare subclasses of thermonuclear transients and discovery of unusual classes of exotic transients in the transient data streams as part of the project. This has led to new insights into their production of heavy elements as well as understanding how many ways white dwarfs can explode.
The progress beyond the state-of-the-art has come from two aspects, one is the novel data that is available from the high-cadence surveys and follow-up that the team has access to (in particular the Zwicky Transient Facility), as well as the theoretical modelling efforts that have been performed within the group. The grant has allowed both to be performed within the group and this has greatly enhanced our scientific outputs and our understanding of exotic explosions. We have performed an in-depth study of mutiple progenitor probes of Type Ia supernovae from within hours to days of explosion out to many hundreds of days later, as well as increasing our understanding of the diversity of thermonuclear explosions by finding and following these events in the high-cadence surveys.