Question 1

O-type stars in our galaxy are

Accepted Answer

O-type stars are very rare, constituting less than 1% of the stars in our galaxy. They are massive, luminous, and have very short lifespans compared to other types of stars.

Question 2

Solar-type stars in our galaxy are

Accepted Answer

Solar-type stars are fairly common in our galaxy, making up several percent of the total number of stars. This estimate is based on observations and modeling of the Milky Way, which suggest that there are around 100 billion stars in our galaxy, and that roughly 5 to 10 percent of these are similar in size and temperature to the Sun. While solar-type stars are not the most common type of star in the galaxy, they are considered important for studying the formation and evolution of planetary systems, as they provide a basis of comparison for our own solar system.

Question 3

High mass stars are much less common than low mass stars because they

Accepted Answer

D

Question 4

When a star finally runs out of hydrogen to fuse in its central core

Accepted Answer

When a star exhausts its hydrogen fuel, the core contracts under gravity, but the outer layers expand and the star becomes much larger and brighter, entering the giant or supergiant phase depending on its initial mass.

Question 5

The intrinsic brightness of a star is referred to as its

Accepted Answer

The intrinsic brightness of a star is referred to as its luminosity. Luminosity is defined as the total amount of energy a star emits in all directions every second.

Question 6

M-type stars in our galaxy are

Accepted Answer

M-type stars, also known as red dwarfs, are the most common type of star in our galaxy, making up 75% or more of the stellar population.

Question 7

A star less massive than our Sun

Accepted Answer

Stars less massive than the Sun burn their fuel more slowly and thus have longer lifetimes.

Question 8

Stars are mostly made of

Accepted Answer

According to current understanding, stars are mostly made of hydrogen and helium, with smaller amounts of other elements. This is based on observations and models of stellar evolution.

Question 9

The presence of elements heavier than helium in stars is very important because

Accepted Answer

Elements heavier than helium are formed through stellar nucleosynthesis, which means they are created within stars. These heavy elements are then scattered throughout space when the stars explode as supernovae. These heavier elements are crucial for the formation of planets and eventually life. Without them, our universe would consist only of hydrogen and helium.

Question 10

What is the most common class of star in our galaxy?

Accepted Answer

M-type stars, also known as red dwarfs, make up about 70% of the stars in our galaxy. They are smaller and cooler than other types of stars and can live for trillions of years, which gives any orbiting planets more time to potentially develop life. Therefore, M-dwarfs are of great interest to astronomers searching for habitable exoplanets.

Question 11

What is the minimum possible mass for a star?

Accepted Answer

The minimum mass required for a star to sustain hydrogen fusion in its core is approximately 0.08 solar masses. Below this mass, the object would be a brown dwarf, which cannot sustain hydrogen fusion.

Question 12

The most important property of a star which determines its evolution is its

Accepted Answer

The mass of a star is the most important property that determines its evolution because its mass affects its internal pressures and temperatures, nuclear reactions, lifetimes, and fate. A star's mass determines whether it will be a red giant, white dwarf, neutron star, or black hole, and it also determines the type and duration of each stage of its life cycle. Therefore, the mass of a star is considered the most critical factor that ultimately determines its fate.

Question 13

The color of a star is a measure of its

Accepted Answer

The color of a star is directly related to its surface temperature. Hotter stars appear blue or white, while cooler stars appear yellow, orange, or red. Therefore, the color of a star can be used to infer its surface temperature.

Question 14

What proportion of their lives do stars spend fusing hydrogen to helium in their cores?

Accepted Answer

This is because the process of fusing hydrogen to helium in a star's core is what sustains its energy production through nuclear fusion. This process continues for the majority of a star's "main sequence" life, which is the phase during which they are converting hydrogen into helium. Therefore, approximately 90% of a star's life is spent fusing hydrogen to helium in its core.

Question 15

Compared to young stars, very old stars have

Accepted Answer

Very old stars have had less time to undergo nucleosynthesis, the process by which heavier elements are created from lighter ones in stars. Therefore, they have a lower proportion of elements heavier than helium compared to younger stars.

Question 16

What is the least common class of star in our galaxy?

Accepted Answer

O-type stars are the least common class of star in our galaxy, accounting for less than 0.00003% of all stars. They are also the most massive and hottest, with temperatures reaching over 30,000 Kelvin. M-type stars, on the other hand, are the most common and make up about 76% of all stars. A-type and G-type stars are also more common than O-type stars.

Question 17

One of the fundamental principles of stellar evolution is that the more massive a star is

Accepted Answer

The more massive a star is, the faster it burns through its nuclear fuel, leading to a quicker evolution through its life stages compared to less massive stars.

Question 18

Stars spend most of their lives

Accepted Answer

Stars spend most of their lives fusing hydrogen into helium in their cores through a process called nuclear fusion. This is what provides the energy that makes the star shine and stay stable for millions or even billions of years.

Question 19

A star more massive than our Sun

Accepted Answer

A star more massive than our Sun will have a shorter lifetime. This is because the higher mass results in a stronger gravitational force, which causes the star to burn through its fuel more quickly, resulting in a shorter lifespan. Additionally, more massive stars undergo more violent and energetic nuclear reactions, further shortening their lifetimes.

Question 20

Approximately what proportion of stars have masses lower than the Sun?

Accepted Answer

The majority of stars in the universe are red dwarfs, which are smaller and less massive than the Sun. These stars make up about 70-75% of the stars in the Milky Way, leading to an estimate that around 90% or more of all stars have masses lower than the Sun.

Quiz 11: Extrasolar Planets: Their Nature and Potential Habitability