Type Ia supernova
Type Ia supernovae are thermonuclear stellar explosions arising from white dwarfs in binary systems and are distinguished spectroscopically by the absence of hydrogen and the presence of strong Si II absorption near 6355 Å. Owing to the width–luminosity (Phillips) relation and related standardization methods, they serve as primary distance indicators on the cosmic distance ladder and were central to the discovery of the accelerating expansion of the Universe. Their progenitors, explosion mechanisms, and environmental dependencies remain active areas of research, with single- and double-degenerate scenarios and sub‑Chandrasekhar double detonations all under consideration.
