RR Lyrae Stars

Definition

RR Lyrae stars are a class of variable stars that exhibit periodic fluctuations in brightness, making them useful tools for measuring cosmic distances. These pulsating stars are old, metal-poor stars that serve as standard candles, providing insights into the structure and evolution of the Milky Way galaxy.

5 Must Know Facts For Your Next Test

1. RR Lyrae stars are old, metal-poor stars that belong to the halo population of the Milky Way galaxy.
2. They have periods of variability typically ranging from 0.2 to 1.2 days, with an average period of about 0.5 days.
3. The variations in brightness of RR Lyrae stars are caused by the star's pulsation, with the star expanding and contracting in a regular cycle.
4. RR Lyrae stars are considered standard candles because their intrinsic luminosities are well-understood, allowing astronomers to determine their distances from Earth.
5. By studying the properties of RR Lyrae stars, astronomers can gain insights into the structure and evolution of the Milky Way galaxy, including the age and composition of its halo.

Review Questions

• Explain how the periodic variations in brightness of RR Lyrae stars are related to their use as standard candles for measuring cosmic distances.
  • The periodic fluctuations in the brightness of RR Lyrae stars are caused by the star's pulsation, with the star expanding and contracting in a regular cycle. This pulsation pattern is well-understood, allowing astronomers to determine the intrinsic luminosity of RR Lyrae stars. By comparing the observed, or apparent, brightness of an RR Lyrae star with its known intrinsic brightness, astronomers can calculate the distance to that star using the inverse square law. This makes RR Lyrae stars valuable standard candles for measuring cosmic distances, particularly within the Milky Way galaxy and its halo.
• Describe the relationship between the properties of RR Lyrae stars and the structure and evolution of the Milky Way galaxy.
  • RR Lyrae stars are old, metal-poor stars that belong to the halo population of the Milky Way galaxy. By studying the properties of RR Lyrae stars, such as their periods of variability, intrinsic luminosities, and spatial distribution, astronomers can gain insights into the structure and evolution of the Milky Way. For example, the presence of RR Lyrae stars in the galactic halo suggests that this region is composed of an older, more metal-poor population of stars, which provides clues about the early formation and chemical enrichment of the Milky Way. Additionally, the use of RR Lyrae stars as standard candles allows astronomers to map the three-dimensional structure of the galactic halo, helping to elucidate the overall architecture of the Milky Way.
• Analyze how the study of RR Lyrae stars has contributed to our understanding of the age and composition of the Milky Way galaxy.
  • The study of RR Lyrae stars has been instrumental in advancing our understanding of the age and composition of the Milky Way galaxy. As old, metal-poor stars belonging to the halo population, RR Lyrae variables provide valuable information about the early formation and evolution of the galaxy. Their pulsation periods and intrinsic luminosities, which are well-characterized, allow astronomers to determine their ages, typically around 10-13 billion years old. This suggests that the galactic halo, where RR Lyrae stars are predominantly found, is composed of some of the oldest stellar populations in the Milky Way. Furthermore, the metal-poor nature of RR Lyrae stars indicates that the early Milky Way was relatively unenriched in heavier elements, providing insights into the chemical composition and evolution of the galaxy over time. By studying the properties of RR Lyrae stars, astronomers can piece together a more comprehensive understanding of the Milky Way's age, structure, and the processes that shaped its development.

Related terms

Variable Stars: Variable stars are celestial objects that exhibit periodic or irregular changes in brightness over time, allowing astronomers to study their properties and the underlying physical processes.

Standard Candles: Standard candles are astronomical objects with known intrinsic luminosities, which can be used to measure the distances to other objects by comparing their apparent and absolute brightnesses.

Pulsating Variables: Pulsating variable stars are a class of variable stars that exhibit periodic changes in size and brightness due to the expansion and contraction of their outer layers.