PHYS 1412: Quiz -- The Milky Way/Galaxies

Questions represent four tries. 10 questions per quiz, duplicates removed.

Where are most heavy elements made?

1. in the interstellar medium
2. in stars and supemovae
3. in the Big Bang, when the universe first began
4. none of the above
5. all of the above

What are cosmic rays?

1. subatomic particles that travel close to the speed of light
2. gamma rays and X rays
3. fast-moving dust particles in the interstellar medium
4. any light waves from space
5. lasers used as weapons by extraterrestrials

Why do we believe 90% of the mass of the Milky Way is in the form of dark matter?

1. The orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo.
2. Although dark matter emits no visible light, it can be seen with radio wavelengths, and such observations confirm that the halo is full of this material.
3. Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk, suggesting that the halo is full of dark matter.
4. Our view of distant galaxies is sometimes obscured by dark blotches in the sky, and we believe these blotches are dark matter located in the halo.

What do astronomers consider heavy elements?

1. elements that are heavier than iron
2. elements that are heavier than carbon
3. elements that are heavier than hydrogen
4. elements that are heavier than uranium
5. all elements besides hydrogen and helium

What evidence supports the theory that there is a black hole at the center of our galaxy?

1. We observe an extremely bright X-ray source at the center of our galaxy.
2. We can see gas falling into an accretion disk and central mass at the center of our galaxy.
3. The motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about 1 parsec across.
4. We observe a large, dark object that absorbs all light at the center of our galaxy.
5. All of the above.

There are more large spiral galaxies than there are large elliptical galaxies.

1. True
2. False

Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest?

1. the one that is reddest in color
2. the one that is bluest in color
3. the one that is farthest away
4. the one that is closest to us
5. the one that appears smallest in size

If the actual density of the universe is greater than the critical density, then the universe will someday stop expanding.

1. True
2. False

What makes white-dwarf supernovae good standard candles?

1. They are very bright, so they can be used to determine the distances to galaxies billion of light-years away.
2. They should all have approximately the same luminosity.
3. They occur so frequently that we can use them to measure the distances to virtually all galaxies.
4. We have had several occur close to us in the Milky Way, so we have been able to determine their luminosities very accurately.
5. Both A and B.

What is the most accurate way to determine the distance to a nearby star?

1. radar ranging
2. stellar parallax
3. main-sequence fitting
4. using Cepheid variables
5. Hubble's law

Open clusters and young stars are generally found only in the disk of the galaxy and not in the halo.

1. True
2. False

Approximately 90% of the mass of the Milky Way is located in the halo of the galaxy in the form of dark matter.

1. True
2. False

What is the most abundant molecule in interstellar clouds besides molecular hydrogen?

1. molecular helium
2. water
3. carbon monoxide
4. ammonia
5. methane

How are interstellar bubbles made?

1. by the collapse of a gas cloud to form stars
2. by planetary nebulae from low-mass stars
3. by the winds of massive stars and supernovae
4. by collisions between galaxies
5. by the rapidly rotating magnetic fields of pulsars

What is a shock wave?

1. a wave of pressure that moves faster than the speed of sound
2. a wave of pressure that moves slightly slower than the speed of sound
3. a wave of pressure that moves faster than the speed of light
4. a wave of electromagnetic energy that can create electrical shocks
5. the wave crea ted when protons slam into electrons

How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies?

1. There are no Cepheids in the Milky Way, so his discovery proved that it had to be in another galaxy.
2. He measured the stellar parallax of the Cepheid in Andromeda, was able to determine the distance to it, and showed that it was far outside the Milky Way Galaxy.
3. He used main-sequence fitting to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
4. From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
5. Since a Cepheid is a type of luminous galaxy, when he found it in Andromeda he was able to prove that Andromeda was a separate galaxy from the Milky Way.

What do scientists mean by the critical density of the universe?

1. the minimum density that a universe needs in order to form galaxies
2. the precise density marking the dividing line between a universe that has enough mass to contract again and a universe that will continue to expand forever
3. the minimum density that a universe needs in order to form stars
4. the average density of the space between galaxies
5. the minimum density that a universe needs in order to create hydrogen

Dr. X believes that the Hubble constant is HO = 55 km/ s/Mpc. Dr. y believes it is HO= 80 km/ s /Mpc. Which statement below automatically follows?

1. Dr. X believes that the universe is expanding, but Dr. y does not.
2. Dr. X believes that the Andromeda Galaxy (a member of our Local Group) is moving away from us at a slower speed than Dr. y believes.
3. Dr. X believes that the universe is older than Dr. y believes.
4. Dr. X believes that the universe will someday stop expanding, while Dr. y believes it will expand forever.
5. Dr. X believes that the universe has a much higher density than Dr. y believes.

Why is the Hyades Cluster important for building up a catalog of the true luminosities of main-sequence stars?

1. It is an extremely bright cluster.
2. It is close enough to us that the distance to the cluster stars can be found by stellar parallax.
3. It is an old globular cluster that has been around our galaxy for several billion years.
4. We have brightness measurements for the stars in the cluster over many decades, so we know how the stars vary in brightness.
5. It contains many Cepheid variables.

Which of the following types of galaxies are reddest in color?

1. spirals
2. ellipticals
3. lenticulars

The Sun is located at the edge of the galaxy, approximately 50,000 light-years from the galactic center.

1. True
2. False

Most of the mass of the galaxy is located in the galactic center, in the form of a massive black hole.

1. True
2. False

Observing the galaxy at radio wavelengths allows us to see beyond the dust in the disk of the galaxy that obscures our view.

1. True
2. False

Harlow Shapley concluded that the Sun was not in the center of the Milky Way Galaxy by

1. looking at the shape of the "milky band" across the sky.
2. mapping the distribution of stars in the galaxy.
3. mapping the distribution of globular clusters in the galaxy.
4. mapping the distribution of gas clouds in the spiral arms.
5. looking at other nearby spiral galaxies.

What is a standard candle?

1. an object for which we are likely to know the true luminosity
2. an object for which we can easily measure the apparent brightness
3. a class of objects in astronomy that all have exactly the same luminosity
4. any star for which we know the exact apparent brightness
5. a long, tapered candle that lights easily

If the actual density of the universe is greater than the critical density, then the universe will someday stop expanding.

1. True
2. False

Why are Cepheid variables important?

1. Cepheid variables are stars that vary in brightness because they harbor a black hole.
2. Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.
3. Cepheids are a type of young galaxy that helps us understand how galaxies form.
4. Cepheids are supermassive stars that are on the verge of becoming supernovae and therefore allow us to choose candidates to watch if we hope to observe a supernova in the near future.

Most large galaxies in the universe are

1. elliptical.
2. spiral or lenticular
3. irregular.
4. abnormal.

Approximately how long does it take the Sun to orbit the Milky Way Galaxy?

1. 23,000 years
2. 230,000 years
3. 2.3 million years
4. 230 million years
5. 23 billion years

How can we see through the interstellar medium?

1. by observing in high-energy wavelengths such as X rays and long wavelengths of light such as radio waves
2. by observing only the brightest visible sources
3. by using only the biggest telescopes
4. by using telescopes above the Earth's atmosphere
5. We cannot see through the interstellar medium.

What is SgrA*?

1. a source of bright X-ray emission coming from the entire constellation of Sagittarius
2. a source of bright radio emission in the center of our galaxy
3. a source that is bright in the visible wavelengths in the center of our galaxy
4. the brightest star in the constellation Sagittarius
5. the bulge at the center of our galaxy

What is a superbubble?

1. a very low-density region of interstellar space, formed by the merger of several bubbles
2. a very high-density region of interstellar space, filled with gas ejected from nearby star systems
3. a bubble so large that it fills much of the galactic halo
4. the region of space cleared by a powerful supernova
5. a cloud of gas that can form a million or more stars

Why can't we see past the cosmological horizon?

1. The universe extends only to this horizon.
2. Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
3. We do not have telescopes big enough.
4. We do not have sensitive enough detectors.
5. The cosmological horizon is infinitely far away, and we can't see to infinity.

Spiral galaxies have more gas, dust, and younger stars than elliptical galaxies do.

1. True
2. False

Elliptical galaxies are more likely to be found in clusters than are spiral galaxies.

1. True
2. False

Recall that Hubble's law is written v = HOd, where v is the recession velocity of a galaxy located a distance d away from us, and HO is Hubble's constant. Suppose HO = 65 km/ s/Mpc. How fast would a galaxy located 500 megaparsecs distant be receding from us?

1. 65 km/s
2. 65Mpc/s
3. 32,500 km/s
4. 9 km/s
5. 0.65 times the speed of light

Comments

[amanda]

hi

[Tom]

some of your answers are wrong.

[Shari]

Hi Tom - feel free to note any corrections. If memory serves, there was at least one quiz where my copying and pasting was pretty rushed and I didn't get all of my corrections done. Perhaps this was it. Thanks for your help.