This evolutionary pathway is known as accretion-induced collapse, a process where the stellar remnant accumulates matter transferred to it by a companion star. White dwarfs are stellar remnants with masses close to that of the Sun. While most consist of carbon and oxygen, certain types are composed of oxygen, neon, and magnesium. These oxygen-neon-magnesium white dwarfs are generally denser and more massive than carbon-oxygen counterparts, meaning they require less additional accumulated mass to approach the Chandrasekhar limit of approximately 1.4 solar masses.
Mechanisms of Accretion-Induced Collapse
When carbon-oxygen white dwarfs reach this threshold, they can undergo a Type Ia supernova explosion and be completely destroyed. In contrast, oxygen-neon-magnesium white dwarfs can potentially avoid complete destruction and instead become progenitors of neutron stars, provided the surrounding accretion conditions are met. Study leader Laurenz Tümmler of ETH Zurich noted that a white dwarf’s composition alone is not enough to drive the transformation. The rate at which matter arrives from the donor star must stay within a relatively narrow range. If the transfer rate is too low, nova outbursts can eject a major portion of the accumulated material. Conversely, if the rate is too high, envelope expansion, winds, or component interactions within the binary system can prevent the remnant from reaching the conditions necessary for collapse. When the proper criteria are satisfied, electrons are captured by neon and magnesium nuclei, which reduces the pressure supporting the star and triggers the collapse.
Observational Signatures and Detection
Estimates by the study’s authors suggest that such collapse events should be rare, though the exact rate of occurrence remains highly uncertain. The simulations demonstrated that the most neutron-rich matter is ejected not along the rotation axis, as previously expected by scientists, but rather at intermediate latitudes. In these specific regions, magnetically driven matter flows collide with neutrino-heated winds, meaning the visual appearance of the event may depend heavily on the viewing angle.
According to the models, accretion-induced collapse might manifest as a bright ultraviolet and optical event lasting between two and three days, potentially accompanied by X-ray and longer-lasting radio emissions. The underlying research was published as a preprint on arXiv.
