Question 1

The main difference between Cepheid stars and RR Lyrae stars is:

Accepted Answer

The answer of The main difference between Cepheid stars and...

Question 2

Each stage of nuclear burning in 25 M_⨀ star is __________ in duration than in a star of 15 M_⨀.

Accepted Answer

As the mass of the star increases, the core temperature and pressure also increase leading to faster and more efficient nuclear reactions. Hence, each stage of nuclear burning in a 25 M_⨀ star happens much faster than in a 15 M_⨀ star.

Question 3

Once silicon burning begins to fuse iron in the core of a high-mass main-sequence star,it only has a few __________ left to live.

Accepted Answer

The answer of Once silicon burning begins to fuse iron...

Question 4

Massive stars explode when they:

Accepted Answer

Massive stars (those with more than 8 times the mass of the sun) undergo a series of fusion reactions that produce heavy elements, until they eventually run out of fuel in their core. Once this happens, there is no longer enough outward pressure from fusion to counteract the force of gravity, and the core collapses. This collapse triggers a massive explosion known as a supernova.

Question 5

How does nucleosynthesis depend on the mass of the star?

Accepted Answer

Nucleosynthesis depends on the mass of the star because with increasing mass, the temperature and pressure in the star's core increase, allowing for heavier elements to be synthesized through fusion reactions. Therefore, with increasing mass, heavier elements are formed in the cores of stars.

Question 6

Which of these begins first in the core of a massive star?

Accepted Answer

Hydrogen fusion to helium is the first fusion reaction that occurs in the core of a massive star. This is because the core temperature and pressure are only high enough to sustain this reaction. Once the hydrogen fuel is exhausted, the core contracts and heats up, allowing helium fusion to occur. This process continues with heavier elements until iron is produced, which cannot be fused further without an input of energy.

Question 7

Why does the luminosity of a high-mass star remain nearly constant as the star burns heavy elements in its core,even though it is producing millions of times more energy per second than it did on the main sequence?

Accepted Answer

The answer of Why does the luminosity of a high-mass...

Question 8

Each kilogram of hydrogen that fuses into helium releases about 6 × 10¹⁴ Joules of energy.How many tons of hydrogen are fused each second to power a massive main-sequence star with a luminosity of 100 L_⨀? Note that 1 L_⨀ = 4 × 10²⁶ Joule/second and 1 ton = 10³ kg.

Accepted Answer

The answer of Each kilogram of hydrogen that fuses into...

Question 9

What mechanism drives the pulsations in Cepheid variables?

Accepted Answer

The ionization and recombination of helium is the mechanism that drives the pulsations in Cepheid variables. This process causes the star's outer layers to expand and contract, which in turn changes its luminosity and causes it to pulsate.

Question 10

Massive stars explode soon after fusion to iron begins because:

Accepted Answer

Fusion of elements heavier than iron requires energy, so the star runs out of fuel and cannot hold itself up against gravity, leading to a catastrophic collapse and explosion.

Question 11

Massive stars synthesize chemical elements going from helium up to iron:

Accepted Answer

Heavy element synthesis through fusion reactions only occurs in the core of the star where temperatures and pressures are high enough for nuclear reactions to occur.

Question 12

What causes massive stars to expel their outer layers?

Accepted Answer

Radiation pressure is the force that drives the outer layers of massive stars outwards, causing them to eventually shed their outer layers and become supernovae. This is due to the enormous amount of energy produced by fusion reactions in the core, which creates a high amount of radiation pressure pushing outwards.

Question 13

The luminosity of a Cepheid star varies in time because:

Accepted Answer

The outer envelope of the star pulsates in radius, causing its luminosity to vary over time. This is due to the fact that as the star's radius changes, its surface area also changes, and the temperature and brightness of the surface change as a result. This pulsation in radius is what makes Cepheid stars such useful tools for measuring cosmic distances.

Question 14

If a 25M_⨀ main-sequence star loses mass at a rate of 10⁻⁶ M_⨀/yr,then how much mass will it lose in its lifetime of 3 million years?

Accepted Answer

The star loses mass at a rate of 10⁻⁶ M_⨀/yr over 3 million years, resulting in a total mass loss of 3M_⨀.

Question 15

As a high-mass main-sequence star evolves off the main sequence,it follows a: __________ on the H-R diagram.

Accepted Answer

The answer of As a high-mass main-sequence star evolves off...

Question 16

The collapse of the core of a high-mass star at the end of its life lasts approximately:

Accepted Answer

The collapse of the core of a high-mass star at the end of its life, also known as a supernova, typically only lasts around one second.

Question 17

If you measure the average brightness and pulsation period of a Cepheid variable star,you can also determine its:

Accepted Answer

The average brightness and pulsation period of a Cepheid variable star are related to its intrinsic luminosity and can be used as a standard candle to determine the star's distance from Earth. This is known as the period-luminosity relationship. Therefore, choice C is the best option. The age, rotation period, mass, and composition of the star cannot be determined solely by measuring its brightness and pulsation period.

Question 18

During the main-sequence evolution of a massive star,increasingly heavier elements are fused in the core,giving the core support for:

Accepted Answer

The answer of During the main-sequence evolution of a massive...

Question 19

An iron core cannot support a massive main-sequence star because:

Accepted Answer

Iron cannot fuse to make heavier nuclei and produce energy, which is necessary to support the massive main-sequence star. Once a star's core fuses to iron, it cannot produce more energy by fusion, and the core collapses, leading to a supernova explosion.

Question 20

The nuclear reaction that releases the most energy per kilogram is:

Accepted Answer

Hydrogen fusing to helium in the process of nuclear fusion releases the most energy per kilogram. This is because it follows Einstein's famous equation E=mc², where the mass defect (the difference between the mass of the initial hydrogen and the mass of the resulting helium) is converted into energy. This is the process that powers the sun and other stars in the universe. The other options, such as oxygen fusing to silicon or carbon fusing to magnesium, also release energy in nuclear reactions, but not as much as hydrogen fusing to helium.

Quiz 17: Evolution of High-Mass Stars