RR Lyrae Stars

Definition

RR Lyrae stars are a type of pulsating variable star that exhibit regular changes in brightness due to pulsations in their outer layers. These stars are primarily found in globular clusters and are considered important standard candles for measuring astronomical distances because of their predictable luminosity variations.

5 Must Know Facts For Your Next Test

1. RR Lyrae stars typically have periods of variability ranging from about 0.5 to 1 day, making them some of the fastest pulsating variables.
2. They are mostly horizontal branch stars, indicating they are in a later stage of stellar evolution where helium fusion occurs in their cores.
3. The light curve of an RR Lyrae star shows a characteristic shape with a rapid rise to maximum brightness followed by a slower decline.
4. Because of their consistent luminosity variations, RR Lyrae stars serve as key indicators for measuring distances to globular clusters and other galaxies.
5. RR Lyrae stars are generally found in old stellar populations, which helps astronomers understand the age and evolution of these star systems.

Review Questions

• What characteristics define RR Lyrae stars, and how do these properties make them useful for distance measurement?
  • RR Lyrae stars are characterized by their regular pulsations, with brightness variations typically ranging from 0.5 to 1 day. Their predictable luminosity allows astronomers to use them as standard candles for distance measurement. By observing the period-luminosity relationship, scientists can calculate how far away these stars are, aiding in our understanding of the structure of our galaxy and beyond.
• Compare and contrast RR Lyrae stars with Cepheid variables regarding their pulsation periods and role in distance measurement.
  • RR Lyrae stars have shorter pulsation periods (0.5 to 1 day) compared to Cepheid variables, which can have periods from a few days to several weeks. Both types of stars are used as standard candles for distance measurements; however, RR Lyrae stars are more commonly found in older stellar populations like globular clusters, while Cepheids are typically found in younger populations such as spiral galaxies. This distinction allows astronomers to use both types effectively for different regions of the universe.
• Evaluate the significance of RR Lyrae stars in understanding the evolution of stellar populations within globular clusters.
  • RR Lyrae stars provide significant insights into the evolutionary processes within globular clusters, as they represent a specific phase in stellar evolution where stars have moved off the main sequence and are undergoing helium fusion. By studying their properties and distribution, astronomers can infer the age and chemical composition of the globular clusters they inhabit. The presence of RR Lyrae stars helps identify the history of star formation in these clusters, enhancing our understanding of galactic evolution over cosmic time.

Related terms

Pulsating Variables: A class of variable stars that change in brightness due to periodic expansion and contraction of their outer layers.

Cepheid Variables: A type of pulsating variable star that has a longer period of brightness variation compared to RR Lyrae stars, used as another type of standard candle.

Globular Clusters: Dense groups of stars that are tightly bound by gravity and often contain older stars, including RR Lyrae stars.