Question 1

Which of these statements about a globular cluster is NOT true?

Accepted Answer

Globular clusters do contain main-sequence stars, particularly older, low-mass stars that are still on the main sequence.

Question 2

The period of variability of a Cepheid variable star, which is easily measured, is directly related to which stellar parameter, thereby providing a reliable method for the measurement of distance to stars?

Accepted Answer

The period of variability of a Cepheid variable star is directly related to its luminosity. This relationship, known as the period-luminosity relation, allows astronomers to determine the distance to Cepheid variables by measuring their period of variability and calculating their absolute luminosity.

Question 3

Where do horizontal-branch stars get their energy?

Accepted Answer

Horizontal-branch stars generate energy through both core helium fusion and shell hydrogen fusion. This stage occurs after the red giant phase, where the core contracts and heats up enough for helium to begin fusing into carbon and oxygen, while hydrogen continues to fuse in a shell surrounding the core.

Question 4

What would one expect to find in the population of stars in a globular cluster?

Accepted Answer

Globular clusters are old and contain stars that have evolved into later stages of their life cycles, such as red giants and white dwarfs, as well as dim red stars that are still on the main sequence.

Question 5

How do the stars in a star cluster change with time?

Accepted Answer

The highest-mass stars evolve the most quickly because they burn through their nuclear fuel at a faster rate compared to lower-mass stars. This rapid consumption of fuel leads to a quicker progression through the stages of stellar evolution.

Question 6

What is the MOST important use of Cepheid variables for astronomers?

Accepted Answer

Cepheid variables are crucial for astronomers because their period of pulsation is directly related to their intrinsic brightness. By observing the period of pulsation, astronomers can determine the true brightness of the Cepheid and compare it to its apparent brightness as seen from Earth, allowing them to calculate the distance to the star. This relationship, known as the period-luminosity relation, makes Cepheids important standard candles for measuring cosmic distances.

Question 7

Which of these stars are metal-rich?

Accepted Answer

Population I stars are known to be metal-rich compared to Population II stars, which are older and contain fewer metals. Globular cluster stars and very old stars typically fall under Population II, characterized by their low metallicity.

Question 8

Why should the period-luminosity relationship be different for Type I Cepheids and Type II Cepheids?

Accepted Answer

Type I Cepheids are metal-rich, which affects their opacity and luminosity, leading to a different period-luminosity relationship compared to the metal-poor Type II Cepheids.

Question 9

What is the best way to estimate the age of a star cluster?

Accepted Answer

Plotting stars on a Hertzsprung-Russell (H-R) diagram and observing which stars are still on the main sequence allows astronomers to estimate the age of a star cluster. This method is based on understanding the evolutionary stages of stars and their positions on the H-R diagram.

Question 10

What are the main general features that make clusters of stars useful to astronomers?

Accepted Answer

Clusters of stars are useful to astronomers because they are at the same distance from Earth, which makes comparing their properties easier. They were also formed at approximately the same time from the same cloud of gas and dust, meaning they have a similar chemical composition. This allows astronomers to study the evolution of stars under similar conditions.

Question 11

Why does the Hertzsprung-Russell diagram of a globular cluster NOT contain any stars with high luminosity and high temperature on the main sequence?

Accepted Answer

High-mass stars have much shorter lifespans than low-mass stars. In a globular cluster, which is very old, the high-mass stars would have already evolved off the main sequence into later stages of stellar evolution, such as red giants or supernovae, long ago.

Question 12

The Sun is a member of which one of these stellar groups?

Accepted Answer

The Sun is a member of Population I, which consists of younger stars like our Sun that have a higher metallicity compared to Population II stars. These stars are found in the disk of the galaxy and are associated with spiral arms, where new stars are formed.

Question 13

How do astronomers know that globular clusters are very old?

Accepted Answer

Globular clusters are known to be very old because they lack massive main-sequence stars. Massive stars have shorter lifespans and would have already evolved off the main sequence if the cluster is old. This absence indicates the cluster's age, as massive stars would have already ended their lifecycle in an old cluster.

Question 14

Which of these statements about a globular cluster is NOT true?

Accepted Answer

Globular clusters primarily consist of older, low-mass stars. High-mass stars have shorter lifespans and would have evolved away from the main sequence by the time we observe these clusters.

Question 15

Horizontal-branch stars have a wide range of temperatures and luminosities between 50 and 100 times that of the Sun, so they are in what stage of their lives?

Accepted Answer

Horizontal-branch stars are in the stage of core helium burning and shell hydrogen burning. This phase occurs after the red giant phase, when the core contracts and heats up enough for helium to begin fusing into carbon and oxygen, while hydrogen continues to burn in a shell around the core.

Question 16

Which of these astronomical objects or systems is likely to be the oldest?

Accepted Answer

Globular clusters are among the oldest objects in the universe, containing some of the first stars to form after the Big Bang, often more than 10 billion years old.

Question 17

The characteristic of a globular cluster of stars is

Accepted Answer

Globular clusters are characterized by their large number of stars (often hundreds of thousands), which are generally very old and metal-poor. This is because they formed early in the history of the Universe, at a time when the interstellar medium was not yet enriched with heavy elements produced by previous generations of stars.

Question 18

How many stars are there in a large globular cluster?

Accepted Answer

Large globular clusters typically contain about 1 million stars. These dense collections of stars are found orbiting the outer regions of galaxies, including the Milky Way.

Question 19

The study of stars in clusters has especially helped astronomers to understand

Accepted Answer

Studying stars in clusters allows astronomers to observe stars of similar ages but different masses, helping them understand how stars evolve over time. This comparison is crucial for developing models of stellar evolution.

Question 20

Once astronomers obtain the apparent magnitude for a Cepheid variable star by direct observation and the absolute magnitude from the period-luminosity relation, what do they need to use to find its distance?

Accepted Answer

The distance-magnitude relationship, also known as the distance modulus formula, is used to calculate the distance to a star when its apparent magnitude and absolute magnitude are known. This method is particularly useful for distant objects like Cepheid variable stars, where direct parallax measurements are not feasible.

Quiz 13: The Lives of Stars From Birth Through Middle Age

Which of these statements about a globular cluster is NOT true?

The period of variability of a Cepheid variable star, which is easily measured, is directly related to which stellar parameter, thereby providing a reliable method for the measurement of distance to stars?

Where do horizontal-branch stars get their energy?

What would one expect to find in the population of stars in a globular cluster?

How do the stars in a star cluster change with time?

What is the MOST important use of Cepheid variables for astronomers?

Which of these stars are metal-rich?

Why should the period-luminosity relationship be different for Type I Cepheids and Type II Cepheids?

What is the best way to estimate the age of a star cluster?

What are the main general features that make clusters of stars useful to astronomers?

Why does the Hertzsprung-Russell diagram of a globular cluster NOT contain any stars with high luminosity and high temperature on the main sequence?

The Sun is a member of which one of these stellar groups?

How do astronomers know that globular clusters are very old?

Which of these statements about a globular cluster is NOT true?

Horizontal-branch stars have a wide range of temperatures and luminosities between 50 and 100 times that of the Sun, so they are in what stage of their lives?

Which of these astronomical objects or systems is likely to be the oldest?

The characteristic of a globular cluster of stars is

How many stars are there in a large globular cluster?

The study of stars in clusters has especially helped astronomers to understand

Once astronomers obtain the apparent magnitude for a Cepheid variable star by direct observation and the absolute magnitude from the period-luminosity relation, what do they need to use to find its distance?