Exam 3- Astronomy
If an astronomical object regularly varies in brightness with a period of 1 day, what is the maximum size of the object?
1 light-day
The current value for the Hubble constant is 22 km/s/Mly. This means that a galaxy that is 1 million light-years (Mly) away appears to be moving away from us at a speed of 22 kilometers per second (km/s). How fast would a galaxy 2 million light years away appear to be moving away?
44 km/s
Like all major galaxies, the Milky Way has what in its core?
A supermassive black hole
Active galactic nuclei activity can slow down or shut off new star formation resulting from galactic mergers. This is known as
AGN feedback
Which of these is a method that astronomers use to detect dark matter in galaxy clusters? (SELECT ALL THAT ARE CORRECT.)
Amount of gravitational lensing Amount of X-ray emission of hot gas within the cluster but outside any galaxies Measure velocities at which galaxies are moving, then estimate what the total mass of the cluster must be to keep the individual galaxies from flying out of the cluster
Astronomers have determined that star formation began early in the universe, perhaps only a few hundred million years after the Big Bang. Which of the following is NOT a piece of evidence supporting this claim?
Distant galaxies show enormous redshifts in their spectra.
Consider two galaxies, Galaxy A and Galaxy B. According to Hubble's Law, if Galaxy B is three times farther away from us than Galaxy A,
Galaxy B appears to be moving away from us 3 times faster than Galaxy A.
What method would today's astronomers use to find the distance to a remote quasar?
Hubble's Law
A faint, blue galaxy is observed by astronomers, but it is too faint to get a detailed spectrum. What inferences can astronomers make about this galaxy based on its color?
If the galaxy is blue, it has had a wave of star formation take place within a few million years of that light leaving the galaxy.
What was notable about Edwin Hubble's discovery of a Cepheid variable in the Andromeda "nebula?"
It was the faintest and farthest Cepheid variable ever discovered at the time, meaning it was in a different galaxy.
Before you can use Hubble's Law to get the distance to a galaxy, what observation must you make of that galaxy?
Measure the redshift in the galaxy's spectrum.
The strong source of radio waves at the center of our Galaxy is called
Sagittarius A*
The local group of 54 galaxies to which the Milky Way belongs is named (don't overthink this one...)
The Local Group
In 1785, William and Caroline Herschel mapped the galaxy by counting the stars in different directions in the sky. What about their results has been shown to be correct?
The Sun in within a disk of stars.
How can a black hole be a source of energy if it doesn't let anything, even light, escape?
The energy is coming from matter falling into the black hole but is still outside the event horizon.
In examining the galactic orbital speeds of objects, what did astronomers discover about the Milky Way Galaxy?
The inner regions of the Milky Way orbit slower than predicted by Kepler's and Newton's Laws of Motion.
Why are the spectra of faraway galaxies redshifted? (Careful...)
The light has been stretched on its way to us, because the universe is expanding.
What does the richness or poorness of a galaxy cluster refer to?
The number of galaxies in the cluster
Which of the following is true about the formation of galaxies?
The process of galaxy formation is similar to the formation of solar systems, but on a larger scale.
How do stars interact with the spiral arms of the Milky Way Galaxy?
The spiral arms are regions of higher density; stars move in and out of the arms.
By looking at far away galaxies, astronomers are looking back in time to when they were younger. How do younger galaxies compare to the present day? (SELECT ALL THAT ARE CORRECT.)
There were more faint, gas-rich galaxies Have more irregular shapes Have more rapid star formation Smaller
Which of the following is true about Population II stars?
They are among the first stars to form in the universe, and have low metallicity.
The reason Type Ia supernovae are useful to astronomers for determining distances to other galaxies is that
They are very luminous, and generally reach the same peak luminosity.
Which of the following is true about Population I stars?
They have 1-4% of their mass as atoms heavier than helium
What's going to happen to the Milky Way and Andromeda Galaxies?
They will collide and merge over billions of years.
Which of the following is the origin for not just the formation of individual galaxies but also the large-scale structure of the universe?
Tiny dark matter "seeds" in the hot cosmic soup after the Big Bang
Which of the quasars has the most redshift in its emission lines?
ULAS J1342+0928
What is dark matter?
Unknown, unseen mass in the galaxy that causes objects in the outer regions of the galaxy to orbit faster than they should.
Which of the following statements about dark matter in the Galaxy is FALSE?
While the dark matter cannot be observed with our present-day instruments, we still have a pretty good idea of what it is made.
Where is the Sun located in the Milky Way Galaxy?
Within the disk, about halfway between the core and the outer edge of the disk.
When galaxies that are about the same size collide, it is known as [ ] . When a larger galaxy consumes a smaller galaxy, we call it [ ]
a merger, cannibalism
Which of the following objects would have the largest redshift?
a quasar
What observation in astronomy, made AFTER the discovery of quasars, was a big help to astronomers in figuring out what quasars really are?
at the center of the Milky Way is a black hole with millions of times more mass than the Sun
Counts of galaxies in various directions show that, on the largest scales, the universe is the same everywhere. This is known as the
cosmological principle
In studying the most distant galaxies, astronomers have determined that the universe is expanding, and that the rate of expansion is accelerating. The unknown driving force that is pulling apart spacetime is known as
dark energy
True or False: Elliptical galaxies and spiral galaxies form in the same way.
false
Edwin Hubble's observations showed that (except for our nearest neighboring galaxies), the farther a galaxy is from us, the
faster it appears to be moving away from us
What objects did Harlow Shapley use to determine that the Sun was not at the center of the galaxy?
globular clusters
Which of the following would have the highest mass-to-light ratio, one measure of the presence of dark matter?
groups of galaxies
If a galaxy contains a great deal of dark matter, what will that do to the galaxy's mass-to-light ratio?
increase it a large amount
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
An astronomer needs to measure the mass of a spiral galaxy. Which of the following observations would be important to make?
measure the speed at which stars or gas near the outer regions of the galaxy are moving
How are galaxies and quasars related?
quasars are active supermassive black holes at the centers of galaxies
What makes astronomers think that the energy source in quasars is only a few light-months across?
quasars show variations in their energy output that have a period of a few months
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
The Milky Way is what type of galaxy?
spiral
The Tully-Fisher relation only can be used for which objects?
spiral galaxies
If a merger involves at least one galaxy rich in interstellar matter, the resulting compression of the gas will result in a burst of star formation. Galaxies where this happens are known as
starburst galaxies
A large-scale structure consisting of many galaxy clusters is called a
supercluster
Many quasars appear to be faint blue stars. What about them so surprised astronomers when they were discovered?
the spectral lines were hard to recognize, before astronomers realized they were extremely redshifted.
Edwin Hubble developed a classification scheme for galaxies. By what characteristic did he classify galaxies?
their shape
Superclusters fill only about 10% of space in the universe. The other 90% consists of mostly empty "bubbles" known as
voids
