Question 1

If a star's pressure increases in its interior to push the star outward, its temperature will drop, causing the star to contract and eventually return to equilibrium.

Accepted Answer

This is a description of how stars maintain hydrostatic equilibrium. When the pressure inside a star increases, it expands, which in turn decreases its internal temperature and pressure (due to the gas laws). This reduction in temperature and pressure causes the star to contract, moving it back towards a state of equilibrium. This process is part of the star's natural cycle of balancing gravitational forces (pulling inward) and pressure (pushing outward).

Question 2

The visual wavelength image shown above is an object that is found in and near star-forming regions.

Accepted Answer

The image is likely showing a nebula, which is a cloud of gas and dust in space where stars are often formed or located nearby. Therefore, the statement is likely true.

Question 3

Bok globules are small, dark fragments of the interstellar medium.

Accepted Answer

Bok globules are indeed small, dark fragments of the interstellar medium. They are often considered as the embryonic stage of star formation, as they contain gas and dust that can eventually collapse and form stars.

Question 4

Protostars are in hydrostatic equilibrium.

Accepted Answer

Protostars are not in hydrostatic equilibrium because they are still contracting and have not yet reached the stable phase where gravitational forces are balanced by internal pressure, which characterizes stars in hydrostatic equilibrium.

Question 5

Main-sequence stars many times the mass of the Sun produce their energy by the set of nuclear reactions called the CNO cycle.

Accepted Answer

This is true. Main-sequence stars with more than 1.3 solar masses generate energy through the CNO cycle, which involves the fusion of hydrogen into helium using carbon, nitrogen, and oxygen as catalysts. This process is more efficient at higher temperatures and densities, which is why it only occurs in larger stars.

Question 6

YSOs are in hydrostatic equilibrium.

Accepted Answer

Young Stellar Objects (YSOs) are not yet in hydrostatic equilibrium as they are still contracting and accumulating mass, which causes the internal pressure to rise, and will eventually reach a point of equilibrium known as the Zero Age Main Sequence (ZAMS) once stable fusion reactions begin in their cores.

Question 7

T Tauri stars are in hydrostatic equilibrium.

Accepted Answer

T Tauri stars are young, pre-main sequence stars that have not yet reached the state of hydrostatic equilibrium, where the inward gravitational force is balanced by the outward pressure of nuclear fusion at their cores.

Question 8

Pre-main-sequence stars are above and to the right of the main sequence.

Accepted Answer

Pre-main-sequence stars are in the process of contracting and heating up towards the main sequence, so they are younger, hotter, and more luminous than main sequence stars. Therefore, they are located above and to the right of the main sequence on the Hertzsprung-Russell diagram.

Question 9

The thermal motions of the atoms in a gas cloud can make it collapse to form a protostar.

Accepted Answer

The thermal motions of the atoms in a gas cloud actually resist collapse. It is the gravitational attraction between the atoms that can overcome these motions and lead to the collapse of the cloud to form a protostar.

Question 10

The dust in the interstellar medium can make distant stars look redder than they really are.

Accepted Answer

The interstellar dust can scatter and absorb blue light, making stars appear redder than they actually are when observed from Earth. This phenomenon is known as interstellar reddening.

Question 11

The pressure of a gas depends on the temperature and density of the gas.

Accepted Answer

The pressure of a gas is directly proportional to its temperature and density according to the ideal gas law. When the temperature or density of a gas increases, so does its pressure. Therefore, the statement is true.

Question 12

Some massive stars only live a few million years.

Accepted Answer

This statement is true. Massive stars have shorter lifetimes compared to low-mass stars. This is because they burn their fuel at a faster rate and exhaust it quickly. Some massive stars can live for only a few million years before exploding as a supernova.

Question 13

If a star's temperature increases in its interior, then more nuclear reactions will occur to push the star outward and its temperature will drop, causing the star to contract and eventually return to equilibrium.

Accepted Answer

When the temperature in a star's interior increases, it causes an increase in the rate of nuclear reactions, which in turn increases the pressure outward. This expansion cools the star, reducing the rate of nuclear reactions, and gravity will cause the star to contract until hydrostatic equilibrium is re-established.

Question 14

If the Sun ceased to generate nuclear fusion in its core, the Sun would immediately begin to collapse inward.

Accepted Answer

When nuclear fusion stops in the Sun's core, the outward pressure generated by the fusion reactions would no longer counterbalance gravity. As a result, the Sun would begin to collapse inward under its own weight.

Question 15

The above image shows stars behind a cloud.

Accepted Answer

The image shows stars that appear to be located behind a cloud.

Question 16

Both the CNO cycle and the proton-proton fusion chain convert hydrogen to helium using catalysts.

Accepted Answer

The CNO cycle involves catalysts (carbon, nitrogen, and oxygen act as catalysts), but the proton-proton fusion chain does not use catalysts; it directly fuses hydrogen nuclei (protons) into helium.

Question 17

The CNO cycle requires higher temperatures than those needed in the proton-proton fusion chain.

Accepted Answer

The CNO cycle requires temperatures of around 15 million Kelvin, which is higher than the temperatures needed for the proton-proton fusion chain, which only requires temperatures of around 4 million Kelvin.

Question 18

HII regions are found near stars cooler than 25,000 K because large amounts of ultraviolet photons would totally destroy the hydrogen atoms in the gas.

Accepted Answer

HII regions are found near hot, young stars that are much hotter than 25,000 K because their large amounts of ultraviolet photons ionize the hydrogen atoms in the gas, not destroy them.

Question 19

More massive stars have more weight to support, so these stars are more luminous.

Accepted Answer

More massive stars have more gravity acting on their interiors, leading to higher pressures and temperatures. This results in stronger nuclear reactions and greater luminosity.

Question 20

How long a star can stay on the main sequence depends upon its size.

Accepted Answer

The answer of How long a star can stay on...

Quiz 9: The Formation and Structure of Stars