| 其他摘要 | Type Ia supernovae (SNe Ia) are "standardizable candles". At the end of the last century, researchers discovered the accelerated expansion of the universe by means of luminosity distance measurements via SNe Ia, from which the existence of dark energy was derived, which in turn ushered in a new age for cosmology. This work consequently won the 2011 Nobel Prize. However, the origin of SNe Ia, namely the identity of their progenitor systems, remains unknown. The single degenerate (SD) model has been dominant over the past few decades, and is still currently considered one of the most probable candidates for SN Ia progenitors, yet the process of accretion onto a carbon-oxygen white dwarf (CO WD), which is vital to the SD scenario, is not well understood. This work summarizes previous research on SNe Ia in detail, including observational progress, detonation models, and progenitor models, before proceeding to explain the current status and outstanding problems regarding CO WD accretion models. At the end, the author’s work concerning CO WD accretion, as well as its implications for future research, will be introduced.According to research based on steady-state models, accreting WD properties are a direct indicator of their accretion rates. Using MESA, the most advanced stellar evolution code to date, we studied the properties of accreting WDs with an authentic WD model. We assume the accreted material is of a similar chemical composition to solar material. Our study focuses on WD masses ranging from 0.5 to 1.378Msun, and on accretion rates ranging from 10^(-8) to 10^(-5)Msun/yr. Our model yields results similar to the steady-state model: when the accretion rate is too high, the WD will expand into a red giant, while when it is too low, H flashes will occur on the surface of the WD, thereby leaving only a very narrow accretion rate window to allow stable accretion.The Eddington luminosity (EL) is the luminosity at which the photon pressure at the surface of a celestial body is in equilibrium with its gravity. When the luminosity of a star exceeds its EL, it will trigger a phenomenon known as the Super-Eddington Wind (SEW). Previous research on the criteria for SEW focused exclusively on the accretion luminosity. However, if the matter accreted onto the COWD undergoes stable H shell burning, and this H shell is located beneath the WD’s photosphere, the luminosity which arises from this burning can also be used to counter gravity. We found that the SEW is triggered at much lower accretion rates,than previously thought, when the contribution of nuclear burning to the total luminosity is included. In this model, the H inthe accreted material is burnt into He at a rate around $\dot{M}_{\rm Edd}$. If the underlying He is further burnt into C and O, the WD mass then increases and possibly reaches the Chandrasekhar limit and produce a SN Ia. Thus presenting an alternative to the optically thick wind proposed by Hachisu et al. Furthermore, the SEW works in low-metallicity environments. Therefore, our model may explain SNe Ia observed at high redshifts which the optically thick wind cannot explain. |
修改评论