Core-collapse (CC) SNe are thought to originate from massive stars with initial mass of around 8 solar masses or more. However, the association between different classes of CCSNe and various types of massive stars as their progenitors is not yet firmly established. Red supergiants are probably the only one with clear association — to H-rich SNe type II. Wolf-Rayet stars, traditionally thought to be the progenitors of the stripped-envelope type Ib/c SNe, cannot seem to account for all Ib/c events as they are rare. Many, if not most, of type Ib/c SNe are likely to come from interacting binaries with initial masses lower than typical Wolf-Rayet lower mass limit from single stellar evolution. Yellow supergiant, blue supergiant (cf. SN 1987A in the Large Magellanic Cloud), and luminous blue variable stars are among other types of late-phase massive stars complicating the SN type-progenitor picture. Multiplicity is one characteristic common to the majority of massive stars, hence its role especially in mass loss via binary interactions, and in the formation of circumstellar matter (CSM), has to be taken into account to understand CCSNe and related transients — a paradigm shift from the “standard” single stellar evolution. Clearly, there is a need for consistency check with what is known from the massive stars field.
In recent years, owing to large all-sky surveys, a growing number of new transients that do not seem to fit in traditional SN classification schemes are being discovered. The last decade has seen the establishment of these new objects as distinct types of SNe, such as the superluminous SNe, the type-Ibn SNe with He-rich CSM, and the emergence of other objects with peculiar evolutions and luminosities. More recently, puzzling objects such as the so-called fast-blue optical transients (FBOTs) and stripped-SNe with H/He-poor CSM interaction (type-Icn SNe) are starting to attract our attention. All these non-traditional SNe also seem to be related to massive stars, in addition to the classical types Ib/c and II.
This leads to a multitude of questions concerning the nature of the progenitors and the pre-SN evolution. What kind of massive stars give rise to those objects? What parameters differentiate the fates of massive stars? How do massive stars lose mass, and form CSM? Can the transient diversity be matched to the massive star diversity? Are there progenitor analogs in the nearby Universe? Or are we looking at the wrong places? Mass loss seems to be still one of the most important puzzle pieces in our understanding. It is likely that metallicity plays a critical role in massive star evolution, and thus turning the focus to massive stars outside the Milky Way may be the key in understanding the explosions that prefer low metallicity environments such as superluminous SNe and gamma-ray bursts. For decades, we have been too used to SNe in metal-rich, large host galaxies, and similarly, to massive stars in the Milky Way. The interconnections between mass loss, metallicity, binarity, rotation, and magnetic fields, are likely to be different in different environments.
While for the regular SNe our understanding of their progenitors and pre-SN evolutions is still incomplete, we are now faced with these questions also relevant to the more exotic objects. The Legacy Survey of Space and Time (LSST) at Rubin observatory is already around the corner, which along with the ongoing and upcoming transient surveys and facilities such as the Zwicky Transient Factory (ZTF) and the Son of X-Shooter, among others, will deliver a flood of new transient objects from all-sky untargeted positions. With an ever-increasing number of new discoveries there is no doubt that we are bound to encounter more objects with peculiar nature requiring new explanations. Now is the time to get excited, and also at the same time, to reflect back on our collective understanding. This Focus Meeting will be serving as the next checkpoint following previous discussions in 2016 (IAUS 329, “The Lives and Death-Throes of Massive Stars”, New Zealand), 2018 (“Massive Stars and SNe”, Argentina), and 2022 (IAUS 361, “Massive Stars Near and Far”, Ireland), and continuing the South African legacy of IAUS 339 “Southern Horizons in Time-Domain Astronomy”, Stellenbosch (2017), as we embark into the new age of discovery.
Topics included in this meeting:
- Transient surveys and new discoveries
- Observations and progenitors of core-collapse supernovae and related transients, such as superluminous supernovae, fast blue optical transients, and intermediate luminosity transients
- Observations of pre-supernova massive stars and supernova progenitor analogs in the local universe
- Circumstellar environments of massive stars and supernovae interacting with circumstellar medium
- Recent developments in late-stage massive stellar evolution theory
- Role of binary interactions and other mass loss mechanisms