page_title: Horizontal branch
hierarchical_section_title: Horizontal branch
caption_attribution_description: English: 15,000 stars in the Messier 5 globular cluster are plotted on a colour-magnitude diagram. Known red giant branch (RGB), RR Lyrae variable (RR), horizontal branch (HB), and asymptotic giant branch (AGB) stars are marked. Nederlands: Hertzsprung-Russell diagram voor de bolvormige sterrenhoop Messier 5. De rode reuzentak (RGB) is de oranje lijn. Geel is de horizontale tak en blauw de asymptotische reuzentak. In het donkerrood het einde van de hoofdreeks en de subreuzentak.
context_page_description: The horizontal branch is a stage of stellar evolution that immediately follows the red giant branch in stars whose masses are similar to the Sun's. Horizontal-branch stars are powered by helium fusion in the core and by hydrogen fusion in a shell surrounding the core. The onset of core helium fusion at the tip of the red giant branch causes substantial changes in stellar structure, resulting in an overall reduction in luminosity, some contraction of the stellar envelope, and the surface reaching higher temperatures.
context_section_description: The horizontal branch (HB) is a stage of stellar evolution that immediately follows the red giant branch in stars whose masses are similar to the Sun's. Horizontal-branch stars are powered by helium fusion in the core (via the triple-alpha process) and by hydrogen fusion (via the CNO cycle) in a shell surrounding the core. The onset of core helium fusion at the tip of the red giant branch causes substantial changes in stellar structure, resulting in an overall reduction in luminosity, some contraction of the stellar envelope, and the surface reaching higher temperatures.
caption: Hertzsprung–Russell diagram for globular cluster M5, with the horizontal branch marked in yellow, RR Lyrae stars in green, and some of the more luminous red giant branch stars in red
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