page_title: Red-giant branch
section_title: Evolution
hierarchical_section_title: Red-giant branch / Evolution
caption_attribution_description: English: Stellar evolutionary tracks on an HR diagram with text along the Zero Age Main Sequence
context_page_description: The red-giant branch, sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of stellar evolution. It is a stage that follows the main sequence for low- to intermediate-mass stars. Red-giant-branch stars have an inert helium core surrounded by a shell of hydrogen fusing via the CNO cycle. They are K- and M-class stars much larger and more luminous than main-sequence stars of the same temperature.
context_section_description: When a star with a mass from about 0.4 M☉ (solar mass) to 12 M☉ (8 M☉ for low-metallicity stars) exhausts its core hydrogen, it enters a phase of hydrogen shell burning during which it becomes a red giant, larger and cooler than on the main sequence. During hydrogen shell burning, the interior of the star goes through several distinct stages which are reflected in the outward appearance.  The evolutionary stages vary depending primarily on the mass of the star, but also on its metallicity.
caption: Evolutionary tracks for stars of different masses:the 0.6 M☉ track shows the RGB and stops at the helium flash.the 1 M☉ track shows a short but long-lasting subgiant branch and the RGB to the helium flash.the 2 M☉ track shows the subgiant branch and RGB, with a barely detectable blue loop onto the AGB.the 5 M☉ track shows a long but very brief subgiant branch, a short RGB, and an extended blue loop.
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