Glossary term: Horizontal Branch

Description: Stars that are fusing helium to carbon in their cores are called horizontal branch stars. The name arises because these stars lie along a horizontal branch in the HR diagram, displaying a range of "surface" temperatures (effective temperatures) but nearly constant luminosity. These are stars that have evolved beyond the red giant phase with variable amounts of mass (outer layers) lost. Main-sequence stars with mass up to eight times the mass of the Sun can go through this evolutionary phase.

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Term and definition status: This term and its definition is still awaiting approval

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