The Final Helium Flash

On February 20th, 1996, Yukio Sakurai identified what first appeared to be an ordinary nova in the constellation Sagittarius. Further study revealed something far more extraordinary: the star was not undergoing a typical outburst but was instead caught in a rare evolutionary phase.

The object, now known as Sakurai’s Object, was experiencing a final helium flash, a brief reignition of nuclear fusion in the thin shell of helium surrounding its core. This phenomenon occurs when a star that has already shed most of its outer layers suddenly fuses its remaining helium in one last burst of energy. Only one other such event had been identified during the entire 20th century.

Sakurai’s Object, with a mass several times that of the Sun, had already fused most of its hydrogen into helium. As the core contracted and heated, conditions became extreme enough to trigger this final flash, causing the star to brighten dramatically before collapsing again into its late evolutionary state.

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