Galaxy Evolution – Flashcards
Unlock all answers in this set
Unlock answersquestion
how do observations of distant galaxies help us learn about galaxy evolution?
answer
Observations at different distances show galazies of different ages and therefore different stages of evolution.
question
Why are telescopes sometimes called "time machines"
answer
because observations of distant objects reveal them as they were in the past.
question
I observe a galaxy that is 100 million light-years away: what do i see?
answer
the light from the galaxy as it was 100 million years ago and it is redshifted.
question
Which of the following gives the two main assumptions of theoretical models of galaxy evolution?
answer
Hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others.
question
Which of the following processes slowed the collapse of protogalactic clouds?
answer
the shock waves from the exploding supernovae of the earliest stars
question
Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?
answer
a dense cloud with very little angular momentum
question
Why is a dense cloud more likely to produce an elliptical galaxy than a spiral galaxy?
answer
The higher gas density forms stars more efficiently so all the gas is converted into stars before a disk can form.
question
What evidence supports the theory that elliptical galaxies come from denser clouds?
answer
Elliptical galaxies at high redshifts lack young, blue stars
question
If we represent the Milky Way Galaxy as the size of a grapefruit (10-cm diameter), the distance to the Andromeda Galaxy would be about
answer
3 meters.
question
Why should galaxy collision have been more common in the past than they are today?
answer
Galaxies were closer together in the past because the universe was smaller
question
What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?
answer
all of the above
question
Which of the following is not a strong argument for the theory that some large elliptical galaxies formed as the result of galaxy collisions?
answer
Galaxy collisions are common and most galaxies in the universe are elliptical
question
What is a central dominant galaxy
answer
a giant elliptical galaxy at the center of a dense cluster?
question
How many more stars does a starburst galaxy form, in one year, than the Milky Way?
answer
about a hundred
question
Why do we believe that starburst galaxies represent a temporary stage in galaxy evolution?
answer
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.
question
Starburst galaxies produce most of their light in the wavelength range of
answer
the infrared
question
What evidence suggests that small galaxies in our Local Group have undergone two or more starbursts in the past?
answer
We see small galaxies in which many stars have one age and many others have another age that is billions of years old.
question
In the 1960s Maarten Schmidt determined that quasars were very distant objects by
answer
determining their redshifts
question
What is a quasar
answer
the extremely bright center of a distant galaxy, thought to be powered by a massive black hole
question
Which of the following is not true of quasars?
answer
Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time
question
Which of the following is evidence for supermassive black holes in active galaxies?
answer
All of the above
question
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?
answer
Active galactic nuclei tend to become less active as they age.
question
What is a galactic wind?
answer
hot gas erupting into intergalactic space from a large superbubble
question
If an object doubles it luminosity in 10 hours, how large can the emitting source of light be?
answer
about 10 light hours across
question
Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude
answer
the X-ray source is no more than a few light-days in diameter
question
Which of the following is not a piece of evidence supporting the conclusion that active galactic nuclei or powered by accretion disks around massive black holes?
answer
Infrared observations show that many stars are forming near the centers of active galaxies
question
How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?
answer
By gravity, which converts potential energy being shot out as jets by a central black hole kinetic energy, which is then converted to thermal energy by collisions among the particles of matter.
question
Where are the X rays produced that are emitted by quasars and other active galactic nuclei?
answer
in hot gas in an accretion disk around a central black hole
question
How do we know that there are intergalactic clouds between a distant quasar and us?
answer
We see hydrogen absorption lines at redshifts smaller than that of the quasar.
question
What are the typical features seen in quasar absorption lines of intergalactic clouds?
answer
The hydrogen line is wider and lines from heavy elements are weaker at higher redshifts
question
Which of the following cannot be true of the very first stars formed in the Universe?
answer
They may have had rocky planets around them
question
All of the following are true. Which of these gives evidence that quasars were more common in the early stages of the universe?
answer
They are more common at very great distances.
