PHYS 202 Astronomy Exam 4

Which of the following is false?

a) The vacuum speed of light is constant

b) Observers in different frames of reference measure the same vacuum speed of light

c) The absoluteness of the vacuum speed of light is an experimentally-verified fact

d) The vacuum speed of light is the speed limit of the Universe; nothing can move faster than that speed.

e) Light slows down in strong gravitational fields, such as near a black hole.

e) Light slows down in strong gravitational fields, such as near a black hole

Roughly how many star systems are in the Milky Way Galaxy?

a) 1 billion

b) 10 billion

c) 100 billion

d) 100 million

e) 100 trillion

c) 100 billion

Where does most star formation occur in the Milky Way Galaxy today?

a) In the galactic halo

b) In the galactic bulge

c) In the spiral arms of the galactic disk

d) At the galactic center

e) Uniformly throughout the Milky Way Galaxy

c) In the spiral arms of the galactic disk

Why are we unlikely to find terrestrial planets orbiting stars in the galactic halo?

a) Planets around stars are known to be extremely rare.

b) Stars in the galactic halo formed in an environment where there were few heavy elements ("metals") to create rocky planets.

c) Any such planets would have been ejected long ago by galactic mergers.

d) Stars in the galactic halo do not have enough gravity to hold onto planets.

e) Stars in the galactic halo formed in a different way from stars in the galactic disk.

b) Stars in the galactic halo formed in an environment where there were few heavy elements ("metals") to create rocky planets

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

a) From the Galaxy's rotation curve, a graph of the orbital speed of stars far from the galactic center, we calculate these stars are feeling gravitational effects from unseen matter.

b) Although dark matter emits no visible light, it does emit radio waves, and direct observations from radio telescopes conform that the Galaxy's mass is mostly this material.

c) Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least ten times as much matter as we see in our galactic disk, suggesting that the Galaxy's mass is mostly dark matter.

d) Our view of distant galaxies is sometimes obscured by dark blotches in the sky, and we believe these blotches are made of dark matter.

a) From the Galaxy's rotation curve, a graph of the orbital speed of stars far from the galactic center, we calculate these stars are feeling gravitational effects from unseen matter.

What are the oldest members of the Milky Way Galaxy?

a) The Sun and other G stars

b) O stars

c) Red giants in the spiral arms of the galactic disk

d) Cepheid variable stars

e) Globular star clusters

e) Globular star clusters

What is a quasar?

a) A starlike object that actually represents a bright patch of gas in the Milky Way.

b) A very large galaxy thought to be formed by the merger of several smaller galaxies, typically found in the center of a galactic cluster.

c) A specialized astronomical instrument for observing distant stars.

d) The extremely luminous center of a distant galaxy, powered by a supermassive black hole.

e) Another name for very luminous stars of spectral type O.

d) The extremely luminous center of a distant galaxy, powered by a supermassive black hole.

If an object doubles its luminosity in 10 hours, how large can the emitting source of light be?

a) Roughly 10 light-years across

b) Roughly 10 parsecs across

c) Roughly 10 light-hours across

d) Varies depending on how luminous the object is

e) Varies depending on how far away the object is

c) Roughly 10 light-hours across

Most active galacti nuclei (AGNs) are usually found at large distances from us; relatively few nearby galaxies have AGNs. What does this imply?

a) Supermassive black holes existed only when the Universe was young and no longer exist today.

b) AGNs tend to become less active as they age.

c) AGNs can form only at large distances from the Milky Way.

d) The jets seen in many AGNs must cause them to move far from us.

b) AGNs tend to become less active as they age.

Where are the X-rays produced that are emitted by quasars and other active galactic nuclei?

a) In hot gas in an accretion disk around a central, supermassive black hole.

b) In ionization nebulae of interstellar gas that surround the accretion disk.

c) In dust grains in molecular clouds that orbit the active galactic nucleus.

d) In fast-moving electrons that jet from the active galactic nucleus.

e) All of the above

e) All of the above

What two quantities did Edwin Hubble plot against each other to discover the expansion of the Universe?

a) Recessional speed and distance

b) Recessional speed and luminosity

c) Recessional speed and temperature

d) Distance and luminosity

e) Distance and temperature

a) Recessional speed and distance

Which of the following statements about the Cosmic Photon Background Radiation is false?

a) It has a present-day temperature of roughly three Kelvins above absolute zero.

b) It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.

c) It had a much hotter temperature in the past.

d) It was first detected by Penzias and Wilson in Holmdel, NJ in the 1960s.

e) It appears essentially the same in all directions (it is isotropic) with only tiny variations.

b) It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.

Because the chemical composition of the universe is about one-quarter helium by mass, no matter where we look, the universe itself must once have been hot enough to fuse hydrogen into helium. (T & F)

True

Suppose we made a rotation curve for the moons orbiting Jupiter. Would it:

a) Rise with increasing distance from Jupiter?

b) Fall with increasing distance from Jupiter?

c) Stay flat with increasing distance from Jupiter?

b) Fall with increasing distance from Jupiter?

Dark matter is purely hypothetical, because we have no way of detecting its presence. (T & F)

False

Gravitational lensing enables us to measure the mass of galaxy clusters (T & F)

True

We can measure a galaxy cluster's mass from the orbital speeds of its galaxies (T & F)

True

Dark matter is probably made of exotic material (not protons, neutrons, and electrons) (T & F)

True

Observations of white dwarf supernovae allow us to measure the distances of very distant galaxies (T & F)

True

Roughly what is the diameter of the Milky Way Galaxy?

a) 100 light-years

b) 1,000 light-years

c) 10,000 light-years

d) 100,000 light-years

e) 1,000,000 light-years

d) 100,000 light-years

Roughly what is the thickness of the disk of the Milky Way Galaxy?

a) 100 light-years

b) 1,000 light-years

c) 10,000 light-years

d) 100,000 light-years

e) 1,000,000 light-years

b) 1,000 light-years

Approximately how far is the Sun from the center of the Galaxy?

a) 25,000 light-years

b) 25 light-years

c) 2,500 light years

d) 250 light-years

e) 25,000,000 light-years

a) 25,000 light-years

Where is our solar system located within the MIlky Way?

a) In the galactic bulge

b) In the galactic disk roughly halfway from the galactic center

c) Near the outskirts of the galactic disk

d) In the galactic halo above the galactic disk

e) In the galactic halo below the galactic disk

b) In the galactic disk roughly halfway from the galactic center

What makes up most of the mass of the Milky Way Galaxy?

a) The dark matter halo

b) The stars in the spiral arms of the galactic disk

c) The stars in the galactic bulge

d) The gas and duct

e) The supermassive black hole at the galactic center

The stars in the spiral arms of the galactic disk

What makes up the interstellar medium?

a) O and B stars

b) K and M stars

c) Gas and dust

d) All of the above

c) Gas and dust

We can study how galaxies evolve because

a) Galaxies are transparent to visible light.

b) We are really smart astronomers.

c) We can watch as they interact in real time.

d) The farther away we look, the further back in time we see.

d) The farther away we look, the further back in time we see.

What do we find within the spiral arms of the galactic disk of the Milky Way Galaxy?

a) O and B stars

b) K and M stars

c) gas and dust

d) All of the above

d) All of the above

Compared with our Sun, how would you describe stars in the galactic halo?

a) Young, blue, bright, and metal-rich

b) Old, red, dim, and metal-poor

b) Old, red, dim, and metal-poor

Compared with elliptical galaxies, how would you describe spiral galaxies?

a) Rounder shapes with younger and bluer stellar populations

b) Rounder shapes with older and redder stellar populations

c) Flatter shapes with younger and bluer stellar populations

d) Flatter shapes with older and redder stellar populations

c) Flatter shapes with younger and bluer stellar populations

The disk component of a spiral galaxy includes which of the following parts?

a) The halo

b) The bulge

c) The spiral arms

d) All of the above

d) All of the above

Which of the following is false?

a) Some quasars are more than a thousand times more luminous than the Milky Way Galaxy.

b) Quasars were common in the past.

c) Quasars are powered by the energy radiated by matter falling into a central, supermassive black hole.

d) Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time.

d) Quasars were powered by the intense production of large numbers of stars that can only be sustained for a relatively short time.

Assume that all the stars in a cluster brighten at the same time. If the cluster doubles its luminosity in 10 hours, how large is the cluster?

a) 10 light-hours across

b) 10 parsecs across

c) 10 light-years across

d) The answer varies depending on how luminous the object is

e) The answer varies depending on how far away the object is

c) 10 light-years across

Irregular galaxies were more common in the past than they are today (T & F)

True

Why should galaxy collisions have been more common in the past than they are today?

a) Galaxies were more active in the past and therefore would have collided with each other more frequently.

b) Galaxies were much bigger in the past since they had not contracted completely.

c) Galaxies were closer together in the past because the universe was smaller.

d) Galaxies attracted each other more strongly in the past because they were more massive; they had not yet turned most of their mass into stars and light.

e) Galaxy collisions shouldn't have been more common in the past than they are now.

c) Galaxies were closer together in the past because the universe was much smaller.

The supermassive black hole at the galactic center makes up roughly 90% of the mass of the Milky Way (T & F)

False

Our solar system is located at the center of the Milky Way Galaxy

(T & F)

False

Most of the current star formation in the Milky Way occurs in the spiral arms of the disk ( T & F)

True

Young stars and open star clusters are generally found only in the galactic disk and not in the galactic halo. (T & F)

True

A protogalactic cloud with very little angular momentum is more likely to form an elliptical galaxy. (T & F)

True

The observable universe is the same size today as it was a few billion years ago ( T & F)

False

Why do we call dark matter "dark"?

a) It emits no visible light

b) We cannot detect the type of radiation that it emits.

c) It emits no or very little radiation of any wavelength.

d) It blocks out the light of stars in a galaxy.

c) It emits no or very little radiation of any wavelength.

We can determine the total visible mass in the universe by using:

a) Gravitational lensing

b) Rotation curves

c) Newton's Law of Gravitation

d) A and B

d) A and B (Gravitational Lensing and Rotation Curves)

Elliptical galaxies are older and are therefore found near the edges of the universe ( T & F)

True

A white dwarf can become a supernova when its mass becomes >1.4(sun), if it draws mass from a companion binary star in its accretion disk (T & F)

True

More distant galaxies have a larger recessional velocity (T & F)

True

In galaxies, individual stars fall apart. This space is filled with dust and dark matter. When galaxies collide, do the individual stars also collide and merge? (Y/N)

No

Is the event horizon the same as the radius of a black hole? (Y/N)

Yes

What is the definition of the event horizon?

a) The radius at which the escape velocity of radiation exceeds the speed of light.

b) Photons emitted by a mass falling into a black hole is gravitationally redshifted beyond the detectable wavelength limit as it tries to escape a large gravitational potential of the space-time fabric.

c) Cannot see anything happening inside the event horizon

d) All of the above

d) All of the above

The mass of a black hole in a galaxy can be calculated from the orbital behavior of bulge and halo stars (T & F)

True