Astronomy 14-17

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(T/F) The Galactic disk contains only old stars.

F

(T/F) Stars and gas in the Galactic disk move in roughly circular orbits around the Galactic center.

T

(T/F) Globular clusters trace out the structure of the Galactic disk.

F

(T/F) Herschel’s attempt to map the Milky Way by counting stars led to an inaccurate estimate of the Galaxy’s size because he was unaware of absorption by interstellar dust.

T

(T/F) The most likely explanation of the high-speed motion of stars and gas near the Galactic center is that they are orbiting a supermassive black hole.

T

(T/F) Cepheid variables can be used to determine the distances to the nearest galaxies.

T

(T/F) The Galactic halo contains as much gas and dust as the disk.

F

(T/F) We can use 21-cm radiation to study molecular clouds.

F

Most of the mass of the Milky Way exists in the form of
A. dust.
B. stars.
C. dark matter.
D. gas.

C. dark matter.

The location of the galactic center was identified using
a) supernova remnants.
b) white dwarf stars in the spiral arms.
c) red giant variable stars in globular clusters.
d) bright O and B stars in open clusters.
e) X-ray sources.

c) red giant variable stars in globular clusters. Explanation: Harlow Shapley used pulsating RR-Lyrae variables as distance indicators to the globular clusters. He then deduced the distance and direction of the Milky Way’s center.

When we observe stars near the center of the Milky Way Galaxy, we detect light that was emitted from those stars about:
a) 200 million years ago
b) 25,000 years ago
c) 8 years ago
d) 8 minutes ago
e) when the galaxy was formed.

b) 25,000 years ago Explanation: (8000 pc)(3.3 ly/pc) ~ 25,000 ly

Our Sun is located in the Milky Way Galaxy
a) about 30 Kpc from the center in the halo.
b) 30,000 light-years from the center in a globular cluster.
c) at the outer edge of the galactic disk, in the plane.
d) about halfway from the center, in the spiral arms.
e) in the bulge, near the Orion arm.

d) about halfway from the center, in the spiral arms. Explanation: The Sun orbits the center of the Galaxy within the disk, taking about 225 million years to complete one orbit.

What two observations allow us to estimate the Galaxy’s mass?
a) the Sun’s mass and velocity in orbit around the galactic center
b) the rotation of the bulge and disk components
c) the Sun’s age and age of the globular cluster stars
d) the motion of spiral arms and the mass of the central black hole
e) the orbital period and distance from the galactic center of objects near the edge of the Galaxy

e) the orbital period and distance from the galactic center of objects near the edge of the Galaxy Explanation: Use the modified form of Kepler’s law to find the mass: Total mass = (orbital size)^3 / (orbital period)^2

A telescope searching for newly formed stars would make the most discoveries if it were pointed
a) directly away from the Galactic center
b) perpendicular to the Galactic disk
c) within the spiral arm
d) between spiral arms

b) perpendicular to the Galactic disk

The first stars that formed in the Milky Way now
a) have chaotic orbits
b) orbit in the Galactic plane
c) orbit near the Galactic center
d) orbit in the same direction as the Milky Way spins.

a) have chaotic orbits

Stars in the outermost regions of the Milky Way Galaxy
a) are youngest
b) orbit faster than astronomers would expect based on the Galactic mass we can see
c) are more likely to explode as supernovae
d) are more luminous than other stars

b) orbit faster than astronomers would expect based on the Galactic mass we can see

(T/F) Most galaxies are spirals like the Milky Way.

F

(T/F) Most elliptical galaxies contain only old stars.

T

(T/F) Irregular galaxies, although small, often have lots of star formation taking place in them.

T

(T/F) Type I supernovae can be used to determine distances to galaxies.

T

(T/F) Most galaxies are receding from the Milky Way Galaxy.

T

(T/F) Hubble’s law can be used to determine distances to the farthest objects in the universe.

T

(T/F) Active galaxies can emit thousands of times more energy than our own Galaxy.

T

Using the method of standard candles, we could, in principle, estimate the distance to a campfire if we knew
a) the number of logs used
b) the fire’s temperature
c) the length of time the fire has been burning
d) the type of wood used in the fire

a) the number of logs used

Within 30 Mpc of the Sun, there are about
A. a few thousand galaxies.
B. a few million galaxies.
C. 30 galaxies.
D. 3 galaxies.

A. a few thousand galaxies.

Hubble’s law states that
A. the greater the distance to a galaxy, the fainter a galaxy appears.
B. the greater the distance to a galaxy, the greater is the galaxy’s redshift.
C. more distant galaxies are younger.
D. most galaxies are found in clusters.

B. the greater the distance to a galaxy, the greater is the galaxy’s redshift.

If the light from a galaxy fluctuates in brightness very rapidly, the region producing the radiation must be
a) very large
b) very small
c) very hot
d) rotating very rapidly

b) very small

Quasar spectra
a) are strongly redshifted
b) show no spectral lines
c) look like the spectra of stars
d) contain emission lines from unknown elements

a) are strongly redshifted

Active galaxies are very luminous because they
a) are hot
b) contain black holes in their cores
c) are surrounded by hot gas
d) emit jets

b) contain black holes in their cores

(T/F) Intergalactic gas in galaxy clusters emits large amounts of energy in the form of radio waves.

F

(T/F) Distant galaxies appear to be much larger than those nearby.

F

(T/F) Collisions between galaxies are rare and have little or no effect on the stars and interstellar gas in the galaxies involved.

F

(T/F) The quasar stage of a galaxy ends because the central black hole swallows up all the matter around it.

T

(T/F) Elliptical galaxies may be formed by mergers between spirals.

T

(T/F) The fact that a typical quasar would consume an entire galaxy’s worth of mass in 10 billion years suggests that quasar lifetimes are relatively long.

F

(T/F) On the largest scales, galaxies in the universe appear to be arranged on huge sheets surrounding nearly empty voids.

T

(T/F) The image of a distant quasar can be split into several images by gravitational field of a foreground cluster.

T

A galaxy containing substantial amounts of dark matter will
a) appear darker
b) spin faster
c) repel other galaxies
d) have more tightly wound arms

b) spin faster

According to X-ray observations, the space between galaxies in a galaxy cluster is
a) completely devoid of matter
b) very cold
c) very hot
d) filled with faint stars

c) very hot

The fraction of mass of the universe made up of dark matter is
a) zero
b) less than 10%
c) roughly 50%
d) more than 90%

d) more than 90%

In current theories of galaxy evolution, quasars occur
a) early in the evolutionary sequence
b) near the Milky Way
c) when elliptical galaxies merge
d) late in evolutionary sequence

a) early in the evolutionary sequence

Many nearby galaxies
a) may be much more active in the future
b) contain quasars
c) have radio lobes
d) may have been much more active in the past

d) may have been much more active in the past

(T/F) Deep surveys of the universe indicate that the largest structures in space are about 50 Mpc in size.

F

(T/F) If the universe had an edge, the fact would violate the assumption of isotropy in the cosmological principle.

F

(T/F) Hubble’s law implies that the universe will expand forever.

F

(T/F) The cosmological redshift is a direct measure of cosmic expansion.

T

(T/F) The cosmic microwave background is the highly redshifted radiation of the early Big Bang.

T

(T/F) Observations suggest that the density of the universe is made up mostly of dark matter.

F

(T/F) The microwave background radiation last interacted with matter around the time of decoupling.

T

(T/F) The theory of inflation predicts that the density of the universe is exactly equal to the critical density.

T

Obler’s paradox is resolved by
a) the finite size of the universe
b) the finite age of the universe
c) light from distant galaxies being redshifted so we can’t see them
d) the fact that there is an edge to the universe

a) the finite size of the universe

The galactic distances used to measure the acceleration of the universe are determined by observations of
a) trigonometric parallax
b) line broadening
c) Cepheid variable stars
d) exploding white dwarfs

d) exploding white dwarfs

On the basis of our current best estimate of the present mass density of the universe, astronomers think that
a) the universe is finite in extent and will expand forever
b) the universe is finite in extent and will eventually collapse
c) the universe is infinite in extent and will expand forever
d) the universe is infinite in extent and will eventually collapse

c) the universe is infinite in extent and will expand forever

The age of the universe is estimated to be
a) less than Earth’s age
b) the same age as the Sun
c) the same age off the Milky Way Galaxy
d) greater than the age of the Milky Way Galaxy

d) greater than the age of the Milky Way Galaxy

The horizon problem in the standard Big Bang model is solved by having the universe
a) accelerate
b) inflate rapidly early in its existence
c) have tiny, but significantly fluctuations in temperature
d) geometrically flat

b) inflate rapidly early in its existence

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