What type of supernova occurs due to a white dwarf gaining excessive mass, leading to an explosion?

A Type Ia supernova occurs when a white dwarf, which is a remnant of a star that has exhausted its nuclear fuel, gains excessive mass. This typically happens in a binary system where the white dwarf accretes matter from a companion star. When the mass of the white dwarf approaches the Chandrasekhar limit, which is approximately 1.4 times the mass of the Sun, the pressure and temperature in its core become sufficient to ignite carbon fusion in a runaway reaction. This leads to a catastrophic explosion, resulting in a Type Ia supernova.

In contrast, Type II supernovae are the result of the core collapse of massive stars that have gone through their fusion cycles and developed a supernova progenitor. Type Ib supernovae are similar but occur in stars that have lost their hydrogen layers prior to collapse. Core-collapse supernovae generally refer to those events that occur in massive stars once their nuclear fusion processes can no longer support them against gravitational collapse, unlike the process that triggers a Type Ia supernova. Therefore, Type Ia is the correct classification for the explosion caused by a white dwarf accumulating mass beyond its threshold.