Question 1

What observations confirm the existence of protostars?

Accepted Answer

The answer of What observations confirm the existence of protostars?...

Question 2

____ are small dark nebulae about 1 light-year in diameter that contain 10 to 1,000 solar masses.

Accepted Answer

A)  HI regions 
B)  HII regions 
C)  Emission nebulae 
D)  Bok globules 
E)  Reflection nebulae

Question 3

As a star begin to form the initial energy source is from

Accepted Answer

A)  nuclear fusion. 
B)  nuclear fission. 
C)  gravitational potential energy. 
D)  magnetic fields.

Question 4

What observations reveal star formation in the Orion nebula?

Accepted Answer

The answer of What observations reveal star formation in the...

Question 5

Which of the following is NOT evidence of the existence of an interstellar medium?

Accepted Answer

A)  extinction of light from distant stars 
B)  very narrow calcium absorption lines in the spectra of O and B stars 
C)  reddening of more distant stars 
D)  dark cloud silhouetted against background stars 
E)  molecular absorption lines in the spectra of cool stars

Question 6

The Orion region contains young main-sequence stars and an emission nebula, but the original molecular cloud they formed out of has been dispersed.

Accepted Answer

A) True 
 B)False

Question 7

What must occur for an object to be considered a main-sequence star?

Accepted Answer

A)  hydrostatic equilibrium 
B)  nuclear fusion reaction in the core 
C)  protostar life begins 
D)  both a and b

Question 8

How does a gas cloud become hot enough to ignite nuclear reactions?

Accepted Answer

The answer of How does a gas cloud become hot...

Question 9

Opacity is

Accepted Answer

A)  the balance between the pressure and force of gravity inside a star. 
B)  the force that binds protons and neutrons together to form a nucleus. 
C)  the force that binds an electron to the nucleus in an atom. 
D)  a measure of the resistance to the flow of radiation (photons) through a gas. 
E)  the temperature and density at which a gas will undergo thermonuclear fusion.

Question 10

The hottest stars in the Orion Nebula ____________hydrogen gas and make it _____________.

Accepted Answer

A)  ionize; glow 
B)  neutralize; glow 
C)  ionize; swallow the star

Question 11

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

A) True 
 B)False

Question 12

Why do nuclear fusion reactions only take place in the interior of a star?

Accepted Answer

A)  The magnetic fields are strongest there. 
B)  The temperature is the hottest in the center. 
C)  The density of material is very high in the center. 
D)  Both b and c 
E)  FALSE; Nuclear fusion reactions can take place in the core and corona where temperatures are high enough.

Question 13

What causes the outward pressure that balances the inward pull of gravity in a star?

Accepted Answer

A)  the outward flow of energy 
B)  the opacity of the gas 
C)  the temperature of the gas 
D)  the density of the gas 
E)  c and d

Question 14

Ninety percent of all stars fuse helium to form carbon and lie on the main sequence.

Accepted Answer

A) True 
 B)False

Question 15

T Tauri stars are believed to be young, high-mass main-sequence stars.

Accepted Answer

A) True 
 B)False

Question 16

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

A) True 
 B)False

Question 17

High-mass stars evolve more slowly to the main sequence than lower-mass stars.

Accepted Answer

A) True 
 B)False

Question 18

There is a main-sequence mass-luminosity relation because

Accepted Answer

A)  helium fusion produces carbon. 
B)  stars expand when they become giants. 
C)  more massive stars support their larger weight by making more energy. 
D)  the helium flash occurs in degenerate matter. 
E)  all stars on the main sequence have about the same radius.

Question 19

Why are distant stars redder than nearby stars of the same spectral type?

Accepted Answer

The answer of Why are distant stars redder than nearby...

Question 20

The proton-proton chain

Accepted Answer

A)  combines two hydrogen nuclei to produce a single helium nucleus and energy. 
B)  splits a helium nucleus to produce 4 hydrogen nuclei and energy. 
C)  is the mechanism that increases the temperature between the photosphere and corona of the sun. 
D)  is the interactions between protons in Earth's atmosphere that produces auroras. 
E)  produces energy in the core of the sun in the form of gamma-rays, positrons, and neutrinos.

Exam 9: The Formation and Structure of Stars

What observations confirm the existence of protostars?

____ are small dark nebulae about 1 light-year in diameter that contain 10 to 1,000 solar masses.

As a star begin to form the initial energy source is from

What observations reveal star formation in the Orion nebula?

Which of the following is NOT evidence of the existence of an interstellar medium?

The Orion region contains young main-sequence stars and an emission nebula, but the original molecular cloud they formed out of has been dispersed.

What must occur for an object to be considered a main-sequence star?

How does a gas cloud become hot enough to ignite nuclear reactions?

Opacity is

The hottest stars in the Orion Nebula hydrogen gas and make it _.

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.

Why do nuclear fusion reactions only take place in the interior of a star?

What causes the outward pressure that balances the inward pull of gravity in a star?

Ninety percent of all stars fuse helium to form carbon and lie on the main sequence.

T Tauri stars are believed to be young, high-mass main-sequence stars.

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

High-mass stars evolve more slowly to the main sequence than lower-mass stars.

There is a main-sequence mass-luminosity relation because

Why are distant stars redder than nearby stars of the same spectral type?

The proton-proton chain