Deck 33: Astrophysics and Cosmology

Question 1

Choose the one alternative that best completes the statement or answers the question.
The earth's orbit has a mean radius of $1.5 \times 10 ^ { 8 } \mathrm {~km}$ . Over a six-month period, the apparent position of a particular star varies by $0.00014 ^ { \circ }$ due to parallax. How many kilometers is this star from Earth?

A) $1.2 \times 10 ^ { 17 } \mathrm {~km}$
B) $1.2 \times 10 ^ { 20 } \mathrm {~km}$
C) $1.2 \times 10 ^ { 11 } \mathrm {~km}$
D) $1.2 \times 10 ^ { 14 } \mathrm {~km}$

Answer 1

D

Question 2

Choose the one alternative that best completes the statement or answers the question.
What is the parallax angle for Proxima Centauri, which is Earth's nearest star at $4.3$ ly? The earth's orbit has a mean radius of $1.5 \times 10 ^ { 8 } \mathrm {~km}$ , and $1 \mathrm { ly } = 9.46 \times 10 ^ { 15 } \mathrm {~m}$ .

A) $2.1 \times 10 ^ { - 7 }$ degrees
B) $1.2 \times 10 ^ { - 14 }$ degrees
C) $1.2 \times 10 ^ { - 7 }$ degrees
D) $2.1 \times 10 ^ { - 4 }$ degrees

Answer 2

D

Question 3

Choose the one alternative that best completes the statement or answers the question.
The earth's orbit has a mean radius of $1.5 \times 10 ^ { 8 } \mathrm {~km}$ . Over a six-month period, the apparent position of a particular star varies by $0.00014 ^ { \circ }$ due to parallax. How many light-years is this star from Earth? (1 ly $= 9.46 \times 10 ^ { 15 } \mathrm {~m}$ )

A) $130 \mathrm { ly }$
B) $13 \mathrm { ly }$
C) $0.13 \mathrm { ly }$
D) $1.3 \mathrm { ly }$

Answer 3

B

Question 4

Choose the one alternative that best completes the statement or answers the question.
Four different main-sequence stars are colored blue, orange, red, and yellow. What is their rank from coolest to hottest?

A) orange, blue, yellow, red
B) red, orange, yellow, blue
C) red, yellow, orange, blue
D) blue, yellow, orange, red

Question 5

Choose the one alternative that best completes the statement or answers the question.
The cosmic background radiation corresponds to a temperature of about

A) 20 K.
B) 2.7 K.
C) 1.4 K.
D) 8.0 K.

Question 6

Choose the one alternative that best completes the statement or answers the question.
Black holes

A) are a violation of Einstein's general theory of relativity.
B) are gaps in space, containing no matter.
C) cannot be detected in binary star systems.
D) are predicted by Einstein's special theory of relativity.
E) are the collapsed remnant of giant stars.

Question 7

Choose the one alternative that best completes the statement or answers the question.
The apparent brightness of a star is $1.0 \times 10 ^ { - 12 } \mathrm {~W} / \mathrm { m } ^ { 2 }$ and the peak wavelength in its light is 600 $\mathrm { nm }$ . Assuming it is the same size as our sun and that it radiates like an ideal blackbody, estimate its distance from us, in parsecs. The constant in Wien's law is $0.00290 \mathrm {~m} \cdot \mathrm { K }$ , and 1 parsec is equal to $3.09 \times 10 ^ { 16 } \mathrm {~m} . \left( R _ { \text {sun } } = 6.96 \times 108 \mathrm {~m} , \sigma = 5.67 \times 10 ^ { - 8 } \frac { \mathrm { W } } { \mathrm { m } ^ { 2 } \cdot \mathrm { K } ^ { 4 } } \right)$

A) $1.2 \mathrm { pc }$
B) $120 \mathrm { pc }$
C) $1200 \mathrm { pc }$
D) $12 \mathrm { pc }$

Question 8

Choose the one alternative that best completes the statement or answers the question.
Many supernovas are thought to result in

A) red giant stars.
B) white dwarfs.
C) neutron stars.
D) regular stars like our sun.

Question 9

Choose the one alternative that best completes the statement or answers the question.
When a distant source emits light of a particular wavelength in the visible, and the source is moving away from us, the color of the light appears to us to be shifted toward the

A) red end of the visible spectrum.
B) blue end of the visible spectrum.

Question 10

Choose the one alternative that best completes the statement or answers the question.
Stars A and B are both black holes but have different masses. If the mass of star A is twice as much as the mass of star B, the average density of star A, compared to the average density of star
B will be

A) the same.
B) half as much.
C) one-fourth as much.
D) four times as much.
E) twice as much.

Question 11

Choose the one alternative that best completes the statement or answers the question.
To what radius would the sun have to be compressed in order for it to become a black hole? The mass of the sun is $1.99 \times 10 ^ { 30 } \mathrm {~kg} , G = 6.67 \times 10 ^ { - 11 } \mathrm {~N} \cdot \mathrm { m } ^ { 2 } / \mathrm { kg } ^ { 2 }$ , and $c = 3.00 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s }$

A) $6.96 \times 10 ^ { 8 } \mathrm {~m}$
B) $2950 \mathrm {~m}$
C) $3.72 \times 10 ^ { 4 } \mathrm {~m}$
D) $2.66 \times 10 ^ { 6 } \mathrm {~m}$
E) $1470 \mathrm {~m}$

Question 12

Write the word or phrase that best completes each statement or answers the question.
Suppose a 70-kg student were to be compressed to form a black hole. What would be the
Schwarzschild radius of this black hole? (G = 6.67 × 10-11 N · m2/kg2, c = 3.0 × 108 m/s)

Question 13

Choose the one alternative that best completes the statement or answers the question.
A white dwarf star with a mass equal to that of the sun is about the size of

A) the sun.
B) a proton.
C) the earth.
D) a basketball.

Question 14

Choose the one alternative that best completes the statement or answers the question.
A Hertzsprung-Russell diagram shows stars on a plot of

A) apparent brightness vs. temperature.
B) luminosity vs. distance.
C) magnitude vs. apparent brightness.
D) luminosity vs. temperature.

Question 15

Choose the one alternative that best completes the statement or answers the question.
The appearance of the great range of brightness among stars is due to

A) only to the differences in the amount of light different stars emit.
B) only to the differences in the distances of stars from us.
C) both of the differences indicated above.
D) none of the above answers.

Question 16

Choose the one alternative that best completes the statement or answers the question.
The sun has apparent brightness $B$ at the earth, which is $1.5 \times 10^{8} \mathrm {~km}$ away. What would be the apparent brightness of the sun at Pluto, which is $6.0 \times 10 ^ { 9 } \mathrm {~km}$ from the sun?

A) $0.025 \mathrm {~B}$
B) $0.00063 B$
C) $0.25 B$
D) $0.063 \mathrm {~B}$

Question 17

Choose the one alternative that best completes the statement or answers the question.
Pulsars are rapidly spinning

A) white dwarfs.
B) neutron stars.
C) red giant stars.
D) regular stars like our sun.

Question 18

Choose the one alternative that best completes the statement or answers the question.
In terms of the mass M of our sun, what is the Chandrasekhar limit of stellar mass, below which a star will eventually collapse into a white dwarf?

A) 1.9 M
B) 1.2 M
C) 0.8 M
D) 1.4 M

Question 19

Choose the one alternative that best completes the statement or answers the question.
A star has absolute luminosity equal to that of the sun but is 10 pc away from the Earth. By what factor will it appear dimmer than the sun? The earth is $1.5 \times 10 ^ { 8 } \mathrm {~km}$ from the sun, and 1 parsec is equal to $3.09 \times 10 ^ { 16 } \mathrm {~m}$ .

A) $2 \times 10 ^ { - 9 }$
B) $2 \times 10 ^ { - 11 }$
C) $2 \times 10 ^ { - 15 }$
D) $2 \times 10 ^ { - 13 }$

Question 20

Choose the one alternative that best completes the statement or answers the question.
What mass would have to be compressed to a radius of $1.0 \times 10 ^ { - 15 } \mathrm {~m}$ (the order of magnitude of the radius of an atomic nucleus) in order for it to become a black hole? ( $G = 6.67 \times 10 ^ { - 11 } \mathrm {~N}$ .
$\mathrm { m } ^ { 2 } / \mathrm { kg } ^ { 2 } , c = 3.0 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s }$ )

A) $6.7 \times 10 ^ { 11 } \mathrm {~kg}$
B) $2.2 \times 10 ^ { 3 } \mathrm {~kg}$
C) $1.1 \times 10 ^ { - 6 } \mathrm {~kg}$
D) $8.3 \times 10 ^ { 15 } \mathrm {~kg}$
E) $4.1 \times 10 ^ { - 8 } \mathrm {~kg}$

Question 21

Choose the one alternative that best completes the statement or answers the question.
Estimate the observed wavelength for the $656 \mathrm {~nm}$ line in the spectrum of a star which is 100 million light-years from us if $H = 20 \frac { \mathrm { km } / \mathrm { s } } { \mathrm { Mly } }$ ? $\left( c = 3.00 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s } \right)$

A) $660 \mathrm {~nm}$
B) $640 \mathrm {~nm}$
C) $690 \mathrm {~nm}$
D) $620 \mathrm {~nm}$

Question 22

Choose the one alternative that best completes the statement or answers the question.
If a galaxy is moving away from us at $1.0 \%$ of the speed of light, how far away is it from us if $H = 20 \frac { \mathrm { km } / \mathrm { s } } { \mathrm { Mly } } ? \left( c = 3.00 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s } \right)$

A) 150 thousand ly
B) 150 billion ly
C) 200 million ly
D) 150 million ly
E) $150 \mathrm { ly }$

Question 23

Choose the one alternative that best completes the statement or answers the question.
About $1 \mu \mathrm { s }$ after the Big Bang, the temperature of the universe was about $10 ^ { 13 } \mathrm {~K}$ . What particle kinetic energy (in $\mathrm { eV } )$ does this correspond to? $\left( 1 \mathrm { eV } = 1.60 \times 10 ^ { - 19 } \mathrm {~J} , k = 1.38 \times 10 ^ { - 23 } \mathrm {~J} / \mathrm { K } \right)$

A) $1 \mathrm { TeV }$
B) $1 \mathrm { keV }$
C) $1 \mathrm { GeV }$
D) $1 \mathrm { MeV }$

Question 24

Choose the one alternative that best completes the statement or answers the question.
It can be shown that the approximate age of the universe is $1 / H$ , where $H$ is the Hubble constant Taking $H = 20 \frac { \mathrm { km } / \mathrm { s } } { \mathrm { Mly } }$ , estimate the age of the universe, in years. (1 ly $\left. = 9.46 \times 10^{15} \mathrm {~m} \right)$

A) 15 billion years
B) 15 million years
C) 15 thousand years
D) 50 billion years

Question 25

Choose the one alternative that best completes the statement or answers the question.
Estimate the speed of recession of a galaxy that is 10 billion light-years away if $H = 20 \frac { \mathrm { km } / \mathrm { s } } { \mathrm { Mly } }$ ? $\left( c = 3.00 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s } \right)$

A) $0.5 \mathrm { c }$
B) $0.3 \mathrm { c }$
C) $0.7 \mathrm { c }$
D) $0.1 \mathrm { c }$