How does the interstellar medium obscure our view of most of the galaxy
It absorbs visible, ultraviolet, and some infrared light
Why are we unlikely to find Earth‐like planets around halo stars in the Galaxy
Halo stars formed in an environment where there were few heavy elements to create rocky planets.
What can cause a galactic fountain
A galactic fountain is the result of a series of supernovas within a galaxy
Compared with stars in the disk, orbits of stars in the halo
are elliptical, with random orientation
Why are Cepheid variables important
Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements
How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies
From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy
What is Hubble's law
The recession velocity of a galaxy is directly proportional to its distance from us
) Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest
parallax, main-sequence fitting, Cepheid variables, Tully-Fisher relation, Hubble's law
How do observations of distant galaxies help us learn about galaxy evolution
Observations at different distances show galaxies of different ages and therefore different stages of evolution.
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 that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy
all of the above
Maarten Schmidt determined in the 1960s, that quasars were very distant objects by
He realized that the emission lines were made of hydrogen that were hugely redshifted from their normal wavelengths. He calculated its luminosity and found it to be over a trillion times greater than our sun
Which of the following is not true of quasars
Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time
How is the energy that 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
How do we know that there are intergalactic clouds between a distant quasar and us
We see hydrogen absorption lines at redshifts smaller than that of the quasar.
What do astronomers mean by "dark energy"?
It's some property of gravity we don't as yet understand; an extension of Einstein's theories, such as quantum gravity.
How do we know that there is much more mass in the halo of our galaxy than in the disk
Stars in the outskirts of the Milky Way orbit the galaxy at much higher speeds than we would expect if all the mass were concentrated in the disk
If there is no dark matter in the Milky Way Galaxy, what is the best alternative explanation for the observations
Our understanding of gravity is not correct for galaxy-size scales
A large mass‐to‐light ratio for a galaxy indicates that .
on average, each solar mass of matter in the galaxy emits less light than our Sun
Which of the following statements about rich clusters of galaxies (those with thousands of galaxies) is not true
They are sources of X-ray emission due to the presence of hot, intergalactic gas.
There likely have been numerous collisions among the member galaxies at some time in the past.
Galaxies in the central regions are predominantly spirals, while elliptical galaxies roam the outskirts.
They often have a very large, central dominant galaxy near their center, perhaps formed by the merger of s.everal individual galaxies.
The speeds of the galaxies in the cluster indicate that most of the cluster mass is dark matter.
When does gravitational lensing occur
when masses distort space time, the fabric of the universe and massive objects can act as gravitational lenses that bend light beams passing nearby
Why can't the dark matter in galaxies be made of neutrinos
Neutrinos travel at extremely high speeds and can escape a galaxy's gravitational pull.
What are the candidates for dark matter
Baryonic and Non-Baryonic which is hot dark matter (HDM) and cold dark matter (CDM
Why isn't space expanding within systems such as our solar
system or the Milky Way
Their gravity is strong enough to hold them together against the expansion of the universe
Why can't current theories describe what happened during the Planck era?
We do not yet have a theory that links quantum mechanics and general relativity
A GUT (grand unified theory) refers to theories that
unify the strong force and the electromagnetic and weak forces
What do astronomers mean by inflation
a sudden and dramatic expansion of the universe thought to have occured at the end of the GUT era
What happened to the quarks that existed freely during the particle era
They combined in groups to make protons, neutrons, and their antiparticles
What kinds of atomic nuclei formed during the era of nucleosynthesis
hydrogen and helium and trace amounts of lithium
Why did the era of nuclei end when the universe was about 300,000 years old
The universe had expanded and cooled to a temperature of about 3,000 K, cool enough for stable, neutral atoms to form
Which of the following statements about the cosmic background radiation is not true
It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.
Why does the Big Bang theory predict that the cosmic background radiation should have a perfect thermal radiation spectrum?
The background radiation came from the heat of the universe, with a peak corresponding to the temperature of the universe
What are the two key observational facts that led to widespread acceptance of the Big Bang model
it predicts the radiation that began to stream across the universe at the end of the era of nuclei should still be present today and it predicts that some of the original hydrogen in the universe should have fused into helium during the era of nucleosynthesis