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17 Cards in this Set

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How do observations of distant galaxies help us learn about galaxy evolution?


We can observe the evolution of a single galaxy over time.


We can observe two galaxies merging and what the result is, helping us learn how mergers affect evolution.


We can observe the birth of galaxies.


We can see what our galaxy used to look like and therefore theorize about the physical processes that led to its current appearance.


Observations at different distances show galaxies of different ages and therefore different stages of evolution.

Observations at different distances show galaxies of different ages and therefore different stages of evolution.

Why are telescopes sometimes called "time machines"?


because astronomers can use telescopes to see the Milky Way as it was when it was much younger


because the author, H.G. Wells, used the term to describe telescopes in a book


because observations of distant objects reveal them as they were in the past


because some of the oldest telescopes are still in use today


It's a journalistic misnomer: you cannot travel into the past or the future.



because observations of distant objects reveal them as they were in the past

Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?


a dense cloud with quite a bit of angular momentum


a low-density cloud with quite a bit of angular momentum


a dense cloud with very little angular momentum


a very low-density cloud with very little angular momentum


a very massive cloud with any density and a lot of angular momentum

a dense cloud with very little angular momentum

Why is a dense cloud more likely to produce an elliptical galaxy than a spiral galaxy?


The force of gravity can pull the material into a more spherical shape.


The higher gas density forms stars more efficiently, so all the gas is converted into stars before a disk can form.


The thickness of the dense cloud prevents a disk from forming.


The higher density of gas had a stronger force of gravity, and therefore the cloud collapses more quickly.


The more frequent collisions between particles randomize the particle orbits.

The higher gas density forms stars more efficiently, so all the gas is converted into stars before a disk can form.

What evidence supports the theory that elliptical galaxies come from denser clouds?


Elliptical galaxies have denser stars than spiral galaxies.


Elliptical galaxies are denser than spiral galaxies.


Elliptical galaxies are generally larger than spiral galaxies.


Elliptical galaxies have more gas than spiral galaxies.


Elliptical galaxies at high redshifts lack young, blue stars.

Elliptical galaxies at high redshifts lack young, blue stars.

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


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.


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


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


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


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

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

What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?


the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies


observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy


observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies


observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies


all of the above

all of the above

Why do we believe that starburst galaxies represent a temporary stage in galaxy evolution?


Such galaxies produce so much light that they would have consumed all their gas long ago if they had always been forming stars at this high rate.


We don't see any nearby starburst galaxies.


We observe starbursts to last only a few years at a time.


All starburst galaxies look like normal spiral galaxies, aside from the starbursts.

Such galaxies produce so much light that they would have consumed all their gas long ago if they had always been forming stars at this high rate.

In the 1960s, Maarten Schmidt determined that quasars were very distant objects by


determining how small the source of light was from its variations in luminosity.


determining their parallax angles.


determining their redshifts.


discovering that they were embedded in distant galaxies.


determining how luminous they were.

determining their redshifts.

What is a quasar?


a specialized astronomical instrument for observing distant stars


a starlike object that actually represents a bright patch of gas in the Milk Way


the extremely bright center of a distant galaxy, thought to be powered by a massive black hole


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


another name for very bright stars of spectral type O

the extremely bright center of a distant galaxy, thought to be powered by a massive black hole

Which of the following is evidence for supermassive black holes in active galaxies?


very high speed orbital motions around galactic nuclei


the discovery of powerful jets coming for a compact core


quasars emit approximately equal power at all wavelengths from infrared to gamma rays


rapid changes in the luminosity of the galaxy nucleus


all of the above

all of the above

The most active galactic nuclei are usually found at large distances from us; relatively few nearby galaxies have active galactic nuclei. What does this imply?


The jets seen in many active galactic nuclei must cause them to move far away from us.


Active galactic nuclei tend to become less active as they age.


Massive black holes existed only when the universe was young and no longer exist today.


Active galactic nuclei can form only at large distances from the Milky Way.

Active galactic nuclei tend to become less active as they age.

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


about 10 light-hours across


about 10 parsecs across


about 10 light-years across


varies depending on how far away the object is


varies depending on how luminous the object is

about 10 light-hours across

Which of the following is not a piece of evidence supporting the conclusion that active galactic nuclei are powered by accretion disks around massive black holes?


Infrared observations show that many stars are forming near the centers of active galaxies.


Observed radiation from the galactic center varies significantly in brightness in times as short as a few days.


Radio observations sometimes show long jets of material extending millions of light-years out from the galactic center.


Spectral lines from the galactic center indicated that clouds of gas are orbiting a central object at very high speed.


The total amount of radiation coming from the galactic center is, in some cases, comparable to the amount of radiation put out by 10 billion or more ordinary stars.

Infrared observations show that many stars are forming near the centers of active galaxies.

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


in ionization nebulae of interstellar gas that surround the accretion disk


in hot gas in an accretion disk around a central black hole


in dust grains in molecular clouds that encircle the active galactic nucleus


in fast-moving electrons that jet from the active galactic nucleus


all of the above

in hot gas in an accretion disk around a central black hole

How do we know that there are intergalactic clouds between a distant quasar and us?


We see hydrogen emission lines at redshifts greater than that of a quasar.


We see hydrogen emission lines at redshifts smaller than that of the quasar.


We see that the emission lines from the quasar are lessened by intervening gas and dust.


We see hydrogen absorption lines at redshifts smaller than that of the quasar.


We see hydrogen absorption lines at redshifts greater than that of the quasar.

We see hydrogen absorption lines at redshifts smaller than that of the quasar.

Which of the following cannot be true of the very first stars formed in the Universe?


They may have formed in large clusters.


They may have formed singly, in isolation.


They may have had rocky planets around them.


They may have all exploded as supernovae by now.


Some may still exist in the Milky Way today.

They may have had rocky planets around them.