Type Ia Supernova Explosions in Binary Systems:A Review

Type Ia supernovae(SNe Ia)play a key role in the fields of astrophysics and cosmology.It is widely accepted that SNe Ia arise from thermonuclear explosions of white dwarfs(WDs)in binary systems.However,there is no consensus on the fundamental aspects of the nature of SN Ia progenitors and their actual explosion mechanism.This fundamentally flaws our understanding of these important astrophysical objects.In this review,we outline the diversity of SNe Ia and the proposed progenitor models and explosion mechanisms.We discuss the recent theoretical and observational progress in addressing the SN Ia progenitor and explosion mechanism in terms of the observables at various stages of the explosion,including rates and delay times,pre-explosion companion stars,ejecta–companion interaction,early excess emission,early radio/X-ray emission from circumstellar material interaction,surviving companion stars,late-time spectra and photometry,polarization signals and supernova remnant properties.Despite the efforts from both the theoretical and observational sides,questions of how the WDs reach an explosive state and what progenitor systems are more likely to produce SNe Ia remain open.No single published model is able to consistently explain all observational features and the full diversity of SNe Ia.This may indicate that either a new progenitor paradigm or an improvement in current models is needed if all SNe Ia arise from the same origin.An alternative scenario is that different progenitor channels and explosion mechanisms contribute to SNe Ia.In the next decade,the ongoing campaigns with the James Webb Space Telescope,Gaia and the Zwicky Transient Facility,and upcoming extensive projects with the Vera C.Rubin Observatory's Legacy Survey of Space and Time and the Square Kilometre Array will allow us to conduct not only studies of individual SNe Ia in unprecedented detail but also systematic investigations for different subclasses of SNe Ia.This will advance theory and observations of SNe Ia sufficiently far to gain a deeper understanding of their origin and explosion mechanism.

How to Build the Engine of and to Provide the Fuel for Quasars

We present a model in which a galaxy galaxy merger can provide not only the fuel for quasar activity, but can also build a super massive black hole, i.e., the engine.

Metal Poor Accretion in the Early Universe

In the early Universe, the chemical composition of matter was different from the one today, as then the heavier elements present today were still missing. The structure, evolution and stability of accretion discs in AGNs depends on the chemical composition of the material. I will present first results of model calculations of such primordial accretion discs.For the calculations, I use a generalized viscosity prescription and newly computed opacities in the range 40-40000 K. I will discuss the influence of the primordial chemical composition on the structure and stability of AGN accretion disks and compare them to the present day Universe situation.