Which of these galaxies is most likely to be oldest?
a galaxy in the Local Group
a galaxy observed at a distance of 5 billion light-years
a galaxy observed at a distance of 10 billion light-years
a galaxy in the Local Group
Which of these galaxies would you most likely find at the center of a large cluster of galaxies?
a large spiral galaxy
a large elliptical galaxy
a small irregular galaxy
a large elliptical galaxy
If all the stars on the main sequence of a star cluster are typically only one-hundredth as bright as their main-sequence counterparts in the Hyades Cluster, then that cluster's distance is:
100 times as far as the Hyades's distance.
30 times as far as th
10 times as far as the Hyades's distance.
Which kind of object is the best standard candle for measuring distances to extremely distant galaxies?
a white dwarf
a Cepheid variable star
a white dwarf supernova
a white dwarf supernova
Why do virtually all the galaxies in the universe appear to be moving away from our own?
Because we are located near where the Big Bang happened.
Because we are located near the center of the universe.
Because expansion causes all galaxies to be moving aw
Because expansion causes all galaxies to be moving away from nearly all others.
When we observe a distant galaxy whose photons have traveled for 10 billion years before reaching Earth, we are seeing that galaxy as it was when the universe was
10 billion years old.
7 billion years old.
4 billion years old.
4 billion years old
Which of these items is a key assumption in our most successful models for galaxy formation?
The distribution of matter was perfectly uniform early in time.
Some regions of the universe were slightly denser than others.
Galaxies formed around supermassive
Some regions of the universe were slightly denser than others.
The luminosity of a quasar is generated in a region the size of
the Milky Way.
a star cluster.
the solar system.
solar system
The primary source of a quasar's energy is
chemical energy.
nuclear energy.
gravitational potential energy.
gravitational potential energy.
Contents of the Universe
� "Normal" Matter: 4.4%
- 0.6% stars in galaxies
- 3.8% gas between galaxies
� Dark Matter: 25%
� Dark Energy 71% (Amount of dark energy needed to explain the observed acceleration)
_____ galaxies tend to have _____ rotation curves indicating large amounts of _________
Spiral galaxies tend to have flat rotation curves indicating large amounts of dark matter
Gravitational lensing
is the bending of light rays by gravity, and it
can also tell us a cluster's mass
WIMPS
Models in which dark matter consists of WIMPS predict that the large-scale structure of the universe should be weblike
Will the universe continue expanding forever?
Fate of universe depends on amount of dark matter
But expansion appears to be speeding up!
Estimated age depends on dark matter and dark energy
We measure solar system's mass using planet orbits
� Orb. Period OR � Orb. Velocity
� Avg. Distance � Orbital Radius
� Orbital velocity drops with distance
- Mass is centrally located.
� Orbital velocity does not drop with distance
- Mass is spread over a large region
Rotation curve
A plot of orbital velocity versus orbital radius
**Solar system's rotation curve declines because Sun has almost all the mass
Rotation curve
of Milky Way
stays ______ with
distance
flat
Mass within Sun's
orbit:
1.0 x 1011 MSun
Milky Way total
mass:
~1012 MSun
Elliptical galaxies have _______ spectral
lines, indicating that the stars are orbiting
_________
broad - quickly
These galaxies also
have dark matter
The mass we find from galaxy motions in a cluster is about _____________than the mass in stars!
50 times larger
Clusters contain large amounts of Xray emitting hot gas
Temperature of hot gas (particle motions) tells us cluster mass:
85% dark matter
13% hot gas
2% stars
Gravitational Lensing
Gravitational lensing is the bending of light rays by gravity, and it can also tell us a cluster's mass
Two Basic Options of Dark Matter
� Ordinary Dark Matter (MACHOs)
- Massive Compact Halo Objects are dead
or failed stars in halos of galaxies
� Extraordinary Dark Matter (WIMPs) <- the best bet
- Weakly Interacting Massive Particles: are
mysterious neutrino-like particles
Why we believe WIMPs exist
� There's not enough ordinary matter
� WIMPs could be left over from Big Bang
� Models involving WIMPs explain how galaxy
formation works
After correcting for Hubble's Law, we can see that galaxies are flowing __________
towards the densest regions in space
In a photo like the Hubble Deep Field (Figure 15.1 in your textbook), we see galaxies in many different stages of their lives. In general, which galaxies are seen in the earliest (youngest) stages of their lives?
the galaxies that have the most hot, young
the galaxies that are farthest away
The most basic difference between elliptical galaxies and spiral galaxies is that _________.
elliptical galaxies lack anything resembling the disk of a spiral galaxy
Hubble's galaxy classification diagram (the "tuning fork") ______.
relates galaxies according to their shapes, but not according to any evolutionary status - Hubble once hoped it might us understand galaxy evolution, but we no longer think there is any evolutionary pathway along the branches of the tuning fork.
Using the technique of main-sequence fitting to determine the distance to a star cluster requires that _____.
we have telescopes powerful enough to allow us to identify the spectral types of main-sequence stars of many masses in the cluster
Suppose we observe a Cepheid variable in a distant galaxy. The Cepheid brightens and dims with a regular period of about 10 days. What can we learn from this observation?
We can learn the distance of the galaxy
Does Hubble's law work well for galaxies in the Local Group? Why or why not?
No, because galaxies in the Local Group are gravitationally bound together.
What is the best way to determine a galaxy's redshift?
Take a spectrum of the galaxy, and measure the difference in wavelength of spectral lines from the wavelengths of those same lines as measured in the laboratory
Which statement below correctly describes the relationship between expansion rate and age for the universe?
The faster the rate of expansion, the younger the age of the universe.
What does cosmological redshift do to light?
stretches its wavelength
Why can't we see past the cosmological horizon?
The cosmological horizon is infinitely far away, and we can't see to infinity.
We do not have big enough telescopes.
Beyond the cosmological horizon, we would be looking back to a time before the universe wa
Beyond the cosmological horizon, we would be looking back to a time before the universe was born.
We can study how galaxies evolve because _________.
the farther away we look, the further back in time we see
Which of the following statements is not an assumption used in models of galaxy formation?
The universe started out filled almost uniformly with hydrogen and helium.
Gas contracted to form the disks of galaxies before any stars were born.
Some regions in
Gas contracted to form the disks of galaxies before any stars were born.
One possible explanation for a galaxy's type invokes the angular momentum of the protogalactic cloud from which it formed. Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed due to other int
a spiral galaxy - With a lot of angular momentum, the protogalactic cloud would spin more rapidly as it collapsed, leading to the formation of a disk - which makes it a spiral galaxy.
Which characteristic is not generally true of a starburst galaxy?
Supernovae occur so frequently that their effects combine to drive a galactic wind that blows material into intergalactic space.
Its rate of star formation is many times higher than the rat
The observed features of the starburst are thought to be caused by the presence of a supermassive black hole in the galaxy's center.
Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply?
Active galactic nuclei tend to become less active as they age.
Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude?
The X-ray source is no more than a few light-days in diameter.
The observed relationship between the masses of central black holes and the bulge masses of galaxies implies that:
Galaxy formation and supermassive black hole formation must be related somehow.
Dark matter is inferred to exist because:
we see lots of dark patches in the sky.
it explains how the expansion of the universe can be accelerating.
we can observe its gravitational influence on visible matter.
we can observe its gravitational influence on visible matter.
Dark energy has been hypothesized to exist in order to explain:
observations suggesting that the expansion of the universe is accelerating.
the high orbital speeds of stars far from the center of our galaxy.
explosions that seem to create giant voids betw
observations suggesting that the expansion of the universe is accelerating.
The flat part of the Milky Way Galaxy's rotation curve tells us that stars in the outskirts of the galaxy:
orbit the galactic center just as fast as stars closer to the center.
rotate rapidly on their axes.
travel in straight, flat lines rather than ellip
orbit the galactic center just as fast as stars closer to the center.
A photograph of a cluster of galaxies shows distorted images of galaxies that lie behind it at greater distances. This is an example of what astronomers call:
a gravitational lens