Review-Questions (exam next Thursday, April 06 chapter 21-25) Go Mason! Go Through My Notes.

Review-Questions(exam next Thursday, April 06

chapter 21-25)

Go Mason!

Go Through My Notes

CHAP21Stellar Evolution:

After the Main Sequence

Question 1:• What is happening in the interior of a star that is on the main sequence on the Hertzsprung-

Russell diagram? </div>

• A. Stars that have reached the main sequence have ceased nuclear “burning” and are simply cooling down by emitting radiation.

• B. The star is slowly shrinking as it slides down the main sequence from top left to bottom right.

• C. The star is generating energy by helium fusion, having stopped hydrogen

• D. The star is generating internal energy by hydrogen fusion.

(D)

Question 2:

• Over which of the following stages of stellar evolution does the radius of a star remain approximately constant?

• A. birth and initial formation • B. red giant • C. asymptotic giant branch phase • D. main-sequence phase

(D)

Question 3:• Which of the following statements about the mass and lifetime

of a star is true?

• A. Stars of about one solar mass have the shortest lives; less massive stars evolve slowly and live a longer time, whereas more massive stars have long lives because of the large amount of fuel they contain.

• B. The more massive the star, the faster it will evolve through its life.

• C.The mass of a star has no bearing on the length of a star's life or the speed of its evolution.

• D. The less massive the star, the shorter its life, because it has less hydrogen

(B)

Question 4:

• At which phase of a star's life will nuclear fusion reactions that convert helium into carbon and oxygen in the central core of a star occur?

• A. during and immediately after the (first) red giant or supergiant stage

• B. during the protostar stage, before the main sequence

• C. in the red giant stage, before the helium flash • D. after the main-sequence phase, before the star

becomes a red giant

(A)

Question 5:

• A helium flash occurs in the cores of all stars • A. that contain helium. • B. of more than 2 solar masses. • C. of fewer than 2 solar masses. • D. that have become red giants.

( C )

Question 6:

• The “turnoff” point for a star cluster is the point in the H-R diagram occupied by the

• A. highest-mass main-sequence stars in the cluster.

• B. stars undergoing (or about to undergo) the helium flash.

• C. lowest-mass main-sequence stars in the cluster.

• D. highest-mass stars that have not yet reached the main sequence.

(A)

Question 7:• What characteristic of Cepheid variables makes them

extremely useful to astronomers? • A. Their absolute magnitude is related directly to their

metal content (heavy element abundance). • B. Their absolute magnitude is directly related to their

diameter. • C.Their absolute magnitude is related directly to their

period of pulsation.

• D.Their absolute magnitude is related directly to their surface temperature.

( C )

Question 8:• Which factor, more than any other, modifies the

evolutionary tracks of stars in binary combinations compared to their single star counterparts?

• A. tidal distortion of the shapes of the stars • B. radiation from one star heating the surface of

the second star • C. mass exchange between the stars • D. reduction of the quantum mechanical limitation

on continued shrinking of one star by the gravitational field of the second star

( C )

CHAP22The Death of Stars

Question 1:

• Which physical phenomenon keeps a white dwarf star from collapsing inward on itself?

• A. electron degeneracy or “quantum crowding”

• B. normal gas pressure • C. convection currents or updrafts from the

nuclear furnace • D. the physical size of the neutrons

( A )

Question 2:• A sequence of thermonuclear fusion processes inside

massive stars can continue to transform the nuclei of elements such as carbon, oxygen, etc. into heavier nuclei AND also generate excess energy, up to a limit beyond which no further energy-producing reactions can occur. The element that is produced when this limit is reached is

• A. silicon. • B. oxygen. • C. uranium. • D. iron.

(D)

Question 3:

• The object seen at the center of a planetary nebula is

• A. an accretion disk around a black hole. • B. a planet in the process of forming.• C. composed almost entirely of neutrons, and

is spinning rapidly. • D.the former core of a red giant star, now a

white dwarf star.

(D)

Question 4:• A Type II supernova is the • A. explosion of a single massive star after silicon

burning has produced a core of iron nuclei. • B. explosion of a red giant star as a result of the

helium flash in the core. • C. collapse of a blue supergiant star to form a

black hole. • D. explosion of a white dwarf in a binary star

system after mass has been transferred to it from its companion.

(A)

CHAP23Neutron Stars

Question 1

• A pulsar is most probably formed • A. in the core of a star as it evolves through

its main sequence phase. • B. in the center of a supernova explosion. • C. within a huge gas cloud, by collisions

between stars. • D. just after the formation of a protostar by

gravitational condensation.

(B)

Question 2

• Synchrotron radiation is emitted whenever • A.charged particles are forced to move along

curved paths within a magnetic field. • B. matter and antimatter meet and annihilate.

C.charged particles are accelerated in straight lines into dense gas such as the outer atmosphere of a star.

• D.charged particles move at speeds faster than the speed of light in any medium.

(A)

Question 3• The fastest pulsars, called millisecond pulsars, have periods of

about 1/1000 second. The reason they pulse so much faster than (for example) the Crab and Vela pulsars is that they

• A. were formed from much more massive stars than were the Crab and Vela pulsars, and were spun up more as their cores collapsed to a smaller volume.

• B.are normal pulsars, whereas the Crab and Vela pulsars have been slowed down from millisecond speeds over their long lifetimes. C. are a totally different phenomenon, involving a black hole rather than a neutron

• D. were spun up by mass transferred on to them from a companion in a binary star system.

(D)

Question 4• The nova phenomenon, an occasional and sometimes repeated

intense brightening of a star by a factor of about 106, is caused by

• A. the beam of radiation from a nearby pulsar illuminating the surface of a red giant star and inducing rapid and intense heating.

• B. hydrogen “burning”; explosively on the surface of a white dwarf star after mass transfer from a companion star in a binary system.

• C. the capture and rapid compression of matter by a black hole. • D. the explosion of a single massive star at the end of its

thermonuclear burning phases.

(B )

CHAP24Black Holes

Question 1:• Suppose you are in the Space Shuttle in orbit around the Earth

at a speed of 7 km/s, and at some particular time your direction of travel is straight toward the Sun. The speed of light in a vacuum is 300,000 km/s. What speed will you measure for the light from the Sun?

• A. 300,000 km/s • B. 300,014 km/s because your speed is added to that of the

light and relativistic contraction has shortened your reference meter sticks

• C. 299,993 km/s because relativistic contraction has shortened all distances, including your reference meter sticks

• D. 300,007 km/s because your speed is added to that of the light

(A)

Question 2:

• What is the correct explanation of the bending of a beam of light as it passes close to a massive object like the Sun?

• A. The gravitational field interacts with the electromagnetic field of the photons to bend the light.

• B. It is traveling across and must follow the curved space surrounding a massive object.

• C. The gravitational field of the massive object changes the refractive index of the nearby space, leading to bending of the light.

• D. The photons of light are attracted by the gravitational field of

the massive object.

(B)

Question 3:

• What is believed to be the maximum mass for a neutron star?

• A.150 solar masses

• B.12 solar masses

• C.3 solar masses

• D.1.4 solar mass

(C )

Question 4:

• What is the event horizon of a black hole? • A. the “surface” from the inside of which nothing can

escape • B. the “surface” at which all “events” or activity

appear to happen because of general relativity • C. the infinitesimally small volume at the center of the

black hole that contains all of the black hole's mass • D. the “surface”; inside which any object entering will

leave with greater energy than that with which it entered

(A)

Question 5:• If you were watching a friend (or better still, an enemy!)

who has fallen as far as the event horizon of a black hole, what would you measure as his heartbeat (apart from effects caused by his adrenaline level)?

• A. It would appear to be normal because gravity has no effect on time intervals.

• B. It would appear to have slowed down somewhat, but not much, because of the change of the speed of light in the gravity field.

• C. It would appear to be zero, his heart would appear to have stopped.

• D. It would appear to have speeded up to an incredible rate.

( C)

CHAP25Galaxy

Question 1:• Interstellar matter blocks our view of the disk

of our galaxy • A. not at all at any wavelength. • B. more-or-less equally at all wavelengths

from radio waves to light waves. • C. most at radio wavelengths, where

hydrogen absorbs radio waves efficiently, and least at optical wavelengths.

• D. more at optical wavelengths, less in the infrared, and not at all at radio wavelengths.

( D )

Question 2:• What happens when the electron in a hydrogen atom

flips its direction of spin, from parallel to antiparallel to that of the proton?

• A. Nothing;this is a forbidden transition and never occurs.

• B. The atom emits a photon of 656.3 nm wavelength (H alpha), in the red region of the spectrum.

• C. The atom emits a photon of 121.5 nm wavelength (Lalpha), in the UV region of the spectrum.

• D. The atom emits a photon of 21-cm wavelength, in the radio region of the spectrum.

( D )

Question 3:• The speed of the Sun in its orbit around the

galaxy is deduced from observations of • A. the galactic center, about which the Sun is

orbiting. • B.Cepheid variables between spiral arms,

because distances can easily be measured to them.

• C.the orbital motions of stars near the Sun. • D. globular clusters in the galactic halo and

distant galaxies.

( D)

Question 4:

• What fraction of the mass of our galaxy is in a form that we have been able to see?

• A. about 10% • B. 100%. Who ever heard of matter that

can't be seen? • C. about 50% • D. about 90%

(A )