Helium star transform into a red giant after losing its hydrogen envelope in the future. Helium star A helium star or helium strong star is a class O or B star (blue), which has extraordinarily strong helium lines and weaker than normal hydrogen lines, indicating strong stellar winds and a mass loss of the outer envelope. "Extreme helium stars" (EHe) entirely lack hydrogen in their spectra. Previously, a "helium star" was a synonym for a B class star, but this usage is considered obsolete. A "helium star" is also a term for a hypothetical star that could occur if two helium white
Red giant temperature and pressure are adequate to cause fusion to resume in a shell around the core. The outer layers of the star then expand greatly, thus beginning the red-giant phase of the star's life. As the star expands, the energy produced in the burning shell of the star is spread over a much larger surface area, resulting in a lower surface temperature and a shift in the star's visible light output towards the red—hence it becomes a "red giant". At this time, the star is said to be ascending the red-giant branch of the Hertzsprung–Russell (H–R) diagram. The evolutionary path