ASTR Unit 4: Chapters 27 & 28
If you wanted to write a complete "cosmic address" for yourself, including every location or structure you live in, which of the following would be that address?
Earth, the Solar System, the Milky Way Galaxy, the Local Group, the Virgo Supercluster
The rich galaxy cluster that is closest to our Local Group of galaxies is the
Virgo Cluster
How do astronomers know that there aren't significant amounts of dark matter within our solar system?
a lot of dark matter would affect the motions (orbits) of our spacecraft as the move through the solar system, and see no such effect
What type of object shows the biggest redshift?
a quasar
By examining rich clusters of galaxies, such as the Coma Clusters, astronomers have discovered that spiral galaxies
are found mostly in the outer regions of such clusters, not in the middle
When quasars "shine" (in visible light and other kinds of radiation) with a lot of energy, where (what location) does this huge amount of energy come from?
from an accretion disk around a supermassive black hole
What do the surveys of the three-dimensional distribution of groups of galaxies reveal about how groups and clusters of galaxies are organized?
galaxy groups are organized into huge filaments with great voids between them -- something like the structure one would see taking a cross-section of some soap bubbles
To map out how clusters of galaxies are distributed in the universe, astronomers needed to know where each cluster was in the sky AND
how far away from us each cluster was
If we want to see what galaxies looked like at a time close to the beginning of the universe, where should we look?
in a direction away from the plane of the Milky Way, where we can see very faint galaxies that are more than 10 billion light years away
According to the Cosmological Principle, the universe
is isotropic and homogeneous
If quasars are at the distances most astronomers believe they are, then (for the most luminous ones) their luminosities must be:
like the combined luminosity of a hundred trillion (1014) Suns
Today, astronomers find compelling evidence that the energy source of the quasars and active galaxies is
matter falling toward a supermassive black hole at the center of a galaxy
Galaxies that we see as they were 11 billion years ago or more, as compared to galaxies today, are generally:
redder and smaller
Today we know that what all quasars have in common is that they appear to be small sources of energy with
redshifts that indicated they are far away
Which of the following observations is a convincing argument for the idea that quasars are located inside galaxies?
relatively nearby quasars show "fuzz" around them with the same spectra and redshift as the quasar
How do astronomers currently think the amount of detectable (observable) matter in the universe compares to the amount of dark matter and dark energy?
the amount of detectable matter is far less than the amount of dark matter & energy
The Hubble Space Telescope has enabled astronomers to explore an active galaxy such as M87 in remarkable detail. Which of the following observations of M87 is NOT an important part of the web of evidence that shows it must have a supermassive black hole at the center?
the discovery of a gravitational lens in M87
If a very distant galaxy looks blue overall to astronomers, from this they can conclude that:
the galaxy must have a lot of young stars and thus active star formation must still be going in it
How do astronomers explain the energetic jets that come out of quasars and active galactic nuclei in opposite directions?
the jets are "spit out" from the chaotic accretion disks of supermassive black holes in directions that are perpendicular to the disk
In which of the following domains of the universe have astronomers NOT found evidence for the presence of dark matter today?
the solar system
When astronomers say that the groups of galaxies are distributed isotropically, they mean that
the way galaxies are arranged in space looks the same in all directions
A distant quasar shows a large redshift -- one so large, in fact, that the features we now see in the visible-light region of the spectrum would be invisible to us, were it not for the redshift. What band of the electro-magnetic spectrum were these features most likely in, before the spectrum was redshifted?
ultraviolet
The "great voids" that astronomers studying galaxies are finding are:
very large regions of intergalactic space, where relatively few galaxies or galaxy clusters can be found
After several decades of observation, astronomers have concluded that quasars are
very powerful and compact sources of energy at the centers of distant galaxies
