Astronomy Chapter 11

How does this "thermostat" regulate nuclear fusion in the core? If the star becomes too hot, it will expand until it cools enough to regain equilibrium. If a star becomes too cool, it will contract until it heats up enough to regain equilibrium. A change in pressure will be balanced by a corresponding change in temperature. All of the above are true.

All of the above are true.

What causes a gas cloud to flatten as it collapses into a star? Conservation of momentum. Conservation of energy. Collisions reduce particle motions perpendicular to the rotational plane. Conservation of angular momentum. Collisions reduce particle motions in the rotational plane.

Collisions reduce particle motions perpendicular to the rotational plane.

Why does a protostellar disks rotation speed up as it shrinks? Newtons 3rd Law Conservation of Momentum Conservation of Angular Momentum Newtons 2nd Law Conservation of Energy

Conservation of Angular Momentum

Ask Your Teacher Based on what you learned about making stars from the interstellar medium, select all of the correct statements from the following list. Gravity causes molecular clouds to contract. Most protostars can be detected by the jets of gas they emit. Protostars are observable at visible wavelengths. There is no resistance to the contraction in a molecular cloud caused by gravity. Gas will heat up as it collapses. There is no evidence that star formation is a continuous process. Stars are born from the gas and dust of the interstellar medium.

Gravity causes molecular clouds to contract. Gas will heat up as it collapses. Stars are born from the gas and dust of the interstellar medium.

If fusion slowed in the core of a main-sequence star, what would happen? Would the star be in hydrostatic equilibrium? Less heat would be produced as fusion slowed, raising the pressure pushing outwards and causing the star to expand in order to maintain hydrostatic equilibrium. Less heat would be produced as fusion slowed, lowering the pressure pushing outwards and causing the star to contract in order to maintain hydrostatic equilibrium. More heat would be produced as fission replaced fusion as the dominant reaction, lowering the pressure pushing outwards and causing the star to contract in order to maintain hydrostatic equilibrium. More heat would be produced as fission replaced fusion as the dominant reaction, raising the pressure pushing outwards and causing the star to expand in order to maintain hydrostatic equilibrium.

Less heat would be produced as fusion slowed, lowering the pressure pushing outwards and causing the star to contract in order to maintain hydrostatic equilibrium.

What happens to the temperature and density inside a collapsing protostar? Temperature decreases and density increases. Temperature and density both increase. Temperature increases and density decreases. Temperature and density both decrease. The product of temperature and density remains constant.

Temperature and density both increase.

How does the CNO cycle differ from the proton-proton chain? The CNO cycle requires a higher temperature than the proton-proton chain and the rate of the CNO cycle is more temperature sensitive than the proton-proton chain. The CNO cycle requires a higher temperature than the proton-proton chain. The rate of the CNO cycle is more temperature sensitive than the proton-proton chain. The energy produced by one sequence through the CNO cycle is greater than for one sequence through the proton-proton chain. all of the above

The CNO cycle requires a higher temperature than the proton-proton chain and the rate of the CNO cycle is more temperature sensitive than the proton-proton chain.

How does the CNO cycle differ from the proton-proton chain? (Select all that apply.) The CNO cycle produces a helium nucleus, whereas the proton-proton chain does not. The CNO cycle produces energy, whereas the proton-proton chain does not. The CNO cycle uses a carbon nucleus as a catalyst for the reaction, whereas the proton-proton chain does not. The CNO cycle requires higher temperatures. The CNO cycle produces different byproducts.

The CNO cycle uses a carbon nucleus as a catalyst for the reaction, whereas the proton-proton chain does not. The CNO cycle requires higher temperatures. The CNO cycle produces different byproducts.

Describe how energy generated in the core of a 1-solar-mass star gets to the star's surface. The energy generated within the core is first transported outward by convective currents, until the gas is no longer opaque. At this point, radiation within the envelope becomes the dominant form of energy transport as photons carry the energy to the surface. The energy generated within the core is first radiated outward until the gas is too opaque for light to easily radiate through. At this point, convection within the envelope becomes the dominant form of energy transport as hot air rises to the surface. The energy generated by a 1-solar-mass star is transported outward along convective currents from the core to the surface. Stars of this mass have high opacity throughout, where convection remains the dominant form of energy transport. The energy generated by a 1-solar-mass star is radiated outward from the core to the surface. Stars of this mass have low opacity throughout, where radiation remains the dominant form of energy transport.

The energy generated within the core is first radiated outward until the gas is too opaque for light to easily radiate through. At this point, convection within the envelope becomes the dominant form of energy transport as hot air rises to the surface.

Which must be true for the state described in part (a) to be maintained? Most of the mass of a star must be in the core. The inner layers of the star must be hotter than the outer layers. The outer layer of a star must be radiative. The outer layers of a star must be convective.

The inner layers of the star must be hotter than the outer layers.

Which is not true about stars that use the CNO cycle? They are massive. They are hot. They are bright. They are long-lived.

They are long-lived.

Which is true about the outer layers of stars that use the CNO cycle? They are radiative only. They are first radiative, then convective. They are convective only. They are first convective, then radiative.

They are radiative only.

They both use a carbon nucleus as a catalyst for the reaction. They occur at similar temperatures. They both produce energy. They both produce the same byproducts. They both produce helium nuclei.

They both produce energy. They both produce helium nuclei.

What kind of gas cloud is most likely to give birth to stars? a cold, low-density gas cloud a hot, low-density gas cloud a hot, dense gas cloud a cold, dense gas cloud

a cold, dense gas cloud

What triggers the gravitational collapse of material inside a molecular cloud? a passing shock wave collisional cooling tidal forces slow the rate of rotation shielding of the interstellar magnetic field a subsidence in turbulence due to internal friction Correct: Your answer is correct.

a passing shock wave

How does a contracting protostar convert gravitational energy into thermal energy? It heats up. Its molecules pick up speed. Gravitational energy is converted to thermal energy. all of the above

all of the above

Which factor resists the contraction of a cloud of interstellar matter? all of the below thermal energy interstellar magnetic field rotation turbulence

all of the below

At any layer in a star, the weight pressing down is _____ the pressure in the gas. greater than less than equal to it depends on the star's temperature

equal to

What is the state described in part (a) called? radiative transfer hydrostatic equilibrium core reduction convective balance

hydrostatic equilibrium

At what wavelengths can we observe the early stages of protostar formation? infrared and visible visible ultraviolet infrared infrared and ultraviolet Correct: Your answer is correct.

infrared

In which component of the interstellar medium do new stars form? hot coronal gas HII intercloud medium HI and molecular clouds HI clouds molecular clouds

molecular clouds

What eventually halts the slow contraction of a newly forming star? a second shock wave the Coulomb barrier gravity nuclear fusion electrostatic repulsion

nuclear fusion

The "thermostat" in a star is a relationship between which of the following? weight and pressure pressure and temperature temperature and weight all three: weight, pressure, and temperature

pressure and temperature

What characteristic of the collapsing cloud that forms a protostar allows it to also form a protostellar disk? rotation thermal energy the interstellar magnetic field turbulence all of the above

rotation

Explain three different ways a giant molecular cloud can be triggered to contract. (Select all that apply.) shock waves passing through molecular clouds mutual attraction between dense cores collisions between molecular clouds the interstellar magnetic field the spiral arms of the Milky Way, through which molecular clouds may pass Correct: Your answer is correct.

shock waves passing through molecular clouds collisions between molecular clouds the spiral arms of the Milky Way, through which molecular clouds may pass

What four factors cause a cloud of interstellar matter to resist contraction? (Select all that apply.) the interstellar magnetic field collisions between molecular clouds thermal energy in the gas the interstellar electric field rotation of the gas cloud turbulence in the interstellar medium Correct: Your answer is correct.

the interstellar magnetic field thermal energy in the gas rotation of the gas cloud turbulence in the interstellar medium

Radiation is ___. the process of transporting energy by photons. the process of transporting heat through the motion of atoms in contact with each other. the process of transporting heat when hot matter rises and cool matter sinks.

the process of transporting energy by photons.

Describe the three ways thermal energy can be transported. Conduction is ___. the process of transporting energy by photons. the process of transporting heat through the motion of atoms in contact with each other. the process of transporting heat when hot matter rises and cool matter sinks.

the process of transporting heat through the motion of atoms in contact with each other.

Convection is ___. the process of transporting energy by photons. the process of transporting heat through the motion of atoms in contact with each other. the process of transporting heat when hot matter rises and cool matter sinks.

the process of transporting heat when hot matter rises and cool matter sink

Most interstellar clouds remain stable in size because the force of gravity is opposed by _______ within the cloud. radiation pressure stellar winds thermal pressure degeneracy pressure

thermal pressure