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Where do RR Lyrae stars appear on a globular cluster’s colour-magnitude diagram?

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Dense cluster of thousands of stars forming a bright, spherical shape in the night sky, representing globular cluster M13. — Globular cluster Globular cluster M13.

On a globular cluster’s colour-magnitude diagram, RR Lyrae stars are located in a specific region known as the RR Lyrae gap. This gap is situated near the blue end of the horizontal branch, which is a distinct feature of the diagrams for these old Population II star systems.12