21st Century Astronomy
21st Century Astronomy
6th Edition
ISBN: 9780393428063
Author: Kay
Publisher: NORTON
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Chapter 20, Problem 1QP
To determine

The size of the Milky Way is determined from studying stars in globular clusters.

Expert Solution & Answer
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Answer to Problem 1QP

Option (c) RR Lyrae is the correct option.

Explanation of Solution

A globular cluster is a spherical collection of stars that orbits a galactic core. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes, and relatively high stellar densities toward their centers.

RR Lyrae stars are easy to spot in globular clusters because they are relatively luminous and have a distinctive light curve. They lie in the instability strip of the Hertzsprung-Russell (H-R) diagram and suffer instabilities that cause their size to periodically change. This change in size also changes the temperature of the star giving rise to their variability.

The size of the Milky Way is determined from studying RR Lyrae stars in globular clusters.

Conclusion:

Since the period-luminosity relationship to determine the distances to globular clusters, option (c) is correct.

RR Lyrae is easy to spot in the globular cluster than the Cepheid variable. Thus, option (a) is incorrect.

Blue supergiant are found towards the top left of H-R diagram. Thus, option (b) is incorrect.

The density of stars inside a globular cluster is significantly higher than the density of stars around the Sun. Thus, option (d) is incorrect.

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Students have asked these similar questions
A group of 10 to 100 stars that formed at the same time but are so widely scattered in space their mutual gravity cannot hold them together is called   a. a globular cluster.   b. an open cluster.   c. an association.   d. a spherical component   e. an accretion disk.
The age of the Milky Way Galaxy has been estimated to be at least 13 billion years based on   a. observations of globular clusters.   b. observations of open clusters.   c. 21-cm radiation from HI regions.   d. the rotation curve of the galaxy.   e. the energy produced by Sagittarius A*.
The approximate diameter of the disk of the Milky Way is   a. 8.0 A.U.   b. 8.0 light-years.   c. 80 light-years.   d. 80,000 light-years.   e. 80,000,000 light-years.
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