Helium flash

A helium flash is a sudden, intense burst of nuclear fusion that occurs in the core of a star like the Sun when it has exhausted its main fuel, hydrogen. As the core contracts and heats up, it reaches a temperature where helium nuclei rapidly fuse into heavier elements, releasing a huge amount of energy in a very short time. This rapid energy release causes the core to expand and stabilize, ending the flash. It marks a key transition in a star's lifecycle, moving from the red giant phase to a stable period of helium burning.