Astronomy Chapter 21 Module 21 HW1 Flashcards


terms in this set (16)

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

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

which of the following gives the two main assumptions of theoretical models of galaxy evolution?

hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others.

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

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

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

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

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

observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies 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
who may have grown by consuming other galaxies ****all of the above

how many more stars does a starburst galaxy form, in one year, than the milky way?

about a hundred

why do we believe
who starburst galaxies represent a temporary stage in galaxy evolution?

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

what first indicated
who the quasars were very distant objects?

determining their redshifts.

what is a quasar?

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

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

the discovery of powerful jets coming from a compact core rapid
transitions in the luminosity of the galaxy nucleus quasars emit as much as equal power at all wavelengths from infrared to gamma rays very high speed orbital motions around galactic nuclei ****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?

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

how is the energy
who powers radio galaxies, quasars, and other active galactic nuclei produced?

by gravity, which converts potential energy of matter falling toward a central black hole into kinetic energy, which is then converted to thermal energy by collisions among the particles of matter

where are the x rays produced that are emitted by quasars and other active galactic nuclei?

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

all of the following are true. which of these gives evidence that quasars were more common in the early stages of the universe?

they are more common at very great distances.

Category: Why question

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