15-16 Flashcards
Most of the light that makes the hazy band of the “milky way” visible in the night sky comes from
reflection and emission nebulae
False
William and Caroline Herschel attempted to make a map of the Milky Way galaxy by counting the
number of stars visible in different directions
true
Harlow Shapley used observations of globular clusters to determine the position of the center of the galaxy.
true
Globular clusters are used as spiral tracers.
false
Stars in the central bulge of the galaxy follow elongated orbits tipped steeply to the plane of the disk
true
The central bulge and the galactic disk of the Milky Way are often referred to as its spherical
component
false
Spiral arms are clearly visible features of galaxies because most sun-like stars in the disk are found
there
false
O and B stars are important spiral tracers
True
A “grand-design” galaxy contains clear spiral arms with few spurs
true
The center of the galaxy has been studied extensively using visible light
false
The mass of the black hole in the center of the galaxy has been determined by observing the motion of stars orbiting it
True
The black hole at the center of our galaxy is too large to be the remnant of a single star
True
The first stars formed in the Universe were composed of 90% hydrogen, 10% helium, and very little
else
true
Stars that formed in the very early stages of our galaxy’s formation have high amounts of “metals.”
False
Population I stars are younger than Population II stars
True
William and Caroline Herschel’s map included four of the following hypotheses in their model of the
galaxy. Which one was the exception?
They provided accurate measurements of the distances to stars.
What property of a Cepheid variable can you determine if you know its period
absolute magnitude
Based on Shapley’s determination of the center of the galaxy, the Sun is located ____
in the middle portion of the galactic disk
The accompanying graph above clearly shows that ____
Type I Cepheid variables are always brighter than Type II Cepheids
Examine the accompanying graph. Harlow Shapley did not know that there are two categories of Cepheid variables; he was only familiar with those such as δ Cepheii. Because of this, some of the
Cepheid variables he observed ____
were dimmer than expected
Which object would be absent in the galactic halo?
emission nebula
The Sun orbits the center of the galaxy about once every ____
200,000,000 years
In which area of the galaxy would you find stars with fairly circular orbits about the galactic center
disk
Almost all of the gas and dust in the Milky Way is located in the ____
disk
The mass of the Milky Way galaxy is a few ___
hundreds of billions of solar masses
The following objects are found in a spiral arm of a galaxy. Which is the exception
population II stars
O stars must be formed in spiral arms because _____.
they do not live long enough to move out of the arm
When you plot the position of sun-like stars, you will find that __
Sun-like stars are found in and out of spiral arms
When you plot the position of sun-like stars, you will find that __
Sun-like stars are found in and out of spiral arms
“Spurs” are probably the result of ____
self-sustaining star formation
Why is it surprising that spiral arms are stable structures, lasting billions of years
Differential rotation should tear the arms apart.
Spiral density wave theory and self-sustaining star formation are ways to explain why ____
molecular clouds are compressed forming young stars along spiral arms
The center of the Milky Way galaxy is in the direction of the constellation ____
Sagittarius
. The center of our galaxy contains a very intense source of radio and X-ray radiation named Sgr A*.
What is it about this source that supports the idea that the radiation comes from a black hole
The radiation is coming from an incredibly small object.
Why is it so difficult to study the center of our galaxy
Interstellar dust blocks almost all light before it reaches Earth.
. The best explanation for the activity at the center of the galaxy is a(n) ____.
black hole with a mass several million times the Sun’s
. Which statement about stellar populations is correct
Population I stars are found in the disk; Population II stars are found in the bulge and halo.
Elements above hydrogen and helium come from _____.
the last phases of stellar evolution and stellar “death
What is the correct ordering of galactic components using the new bottom-up hypothesis starting from
oldest to youngest
galactic halo, average globular clusters, galactic disk
One of the most important features that must be explained by models during the formation of the
galaxy is the ____.
differences in age and metallicity of stars, especially in the hal
What is the monolithic collapse hypothesis unable to explain?
The elongated bar shape of the central bulge
_______________ variable stars are useful in measuring the distance to globular clusters.
Cepheid
In the late 18th century, two astronomers, both with the last name of _______________, were the first
to attempt to map the shape of the galaxy.
Herschel
An astronomer named _______________ used globular clusters to locate the center of the galaxy.
(enter last name only
shapley
The galactic _______________ contains very little gas and dust, old stars, and globular clusters.
halo
Stars at different distances from the galactic center revolve with different periods, an effect called
_______________ rotation
differential
O and B stars only occur in the galactic_____
disk
Objects used to map spiral arms are called spiral _______________.
tracers
. A partial, or detached, segment of a spiral arm is referred to as a(n) “ _______________.
spur
Sgr A* has been heavily studied using _______________ interferometry.
radio
Astronomers refer to elements heavier than helium as _______________
metals
Elliptical galaxies contain a mix of old and young stars
false
When spiral nebulae were first discovered, astronomers quickly identified them as distant groupings of stars
false
Spiral and irregular galaxies have active star formation
true
The diameter and luminosity of a galaxy do not determine its type
true
A standard candle is an object with a known luminosity
true
Globular clusters can be used to measure the distance of nearby galaxies
true
Hubble’s Law is only effective in measuring the distance to nearby galaxies.
false
All elliptical galaxies are more massive than the largest spiral galaxies
false
Galaxies contain 10 times as much dark matter as visible matter
true
Giant spirals are the largest galaxies in the Universe.
false
Gravitational lensing can be used to detect the presence of dark matter
true
Starburst” events are a common outcome of galactic collisions
true
The Milky Way galaxy has collided with several other large galaxies in its lifetime
false
Gentle gravitational tidal forces appear to be necessary to create spiral arms.
true
The farthest galaxies that astronomers have seen are all elliptical galaxies
false
The identification of “spiral nebulae” as large groupings of stars outside of our own galaxy was proven
by ____
photographic plates made by Edwin Hubble showing stars and Cepheid variables
In which of the following types of galaxies would you expect to find active star formation
spiral and irregular
Which types of galaxies lack an ordered structure of stellar orbits
irregular galaxies only
Which types of galaxies would contain very little gas and dust
elliptical galaxies
NASA’s Hubble Deep Field images and GOODS program observations have shown that ____
the entire sky is thickly covered with galaxies.
The structure of most galaxies is most apparent using near-infrared images that show the locations of
____
cool-low luminosity stars
in general
most cataloged galaxies are spiral, but elliptical galaxies are the most common.
Cepheid variables are useful in measuring the distance to ____
galaxies that are within 30 megaparsecs, a relatively short distance
Globular clusters can be used to estimate the distance to galaxies by measuring the clusters’ ____.
angular diameter
An astronomer would find a type Ia supernova in a distant galaxy useful as a(n) ____
standard candle
Cepheids and globular clusters are limited in their ability to measure the distance to galaxies because
they ____.
are not bright enough to detect at large distance
Edwin Hubble and Milton Humason discovered that there was a linear relationship between a galaxy’s
____.
velocity and distance
The Hubble law is one of the most important relations in modern astronomy because it ____
allows astronomers to measure the distance to very distant galaxies using only their
spectrum
Because the Hubble constant has a value of 70 km/s/Mpc, a galaxy 100 Mpc away would have a
recession velocity of ____
7,000 kms
Because the Hubble constant equals 70 km/s/Mpc, a galaxy with a recession velocity of 4,900 km/s
would be a distance of ____ Mpc from Earth.
70
In order to calculate the size and luminosity of a galaxy, you must first determine its ____
distance
Compared to other spiral galaxies, the Milky Way is ____
larger and brighter than most spirals
The range of diameters and luminosities displayed by elliptical galaxies is ____
wider than the range for spirals
The rotation curve of a galaxy is important in determining the galaxy’s ____
mass
The ____ depend(s) on the assumption that the mass of a galaxy or galactic cluster is large enough to
keep moving matter bound to the main structure
velocity dispersion and cluster methods
Dark matter is detectable in the coronae of ____
all galaxies
A key piece of evidence that leads astronomers to conclude that most galaxies include a supermassive
black hole in the center is that ____
stars near the center of other galaxies are orbiting more rapidly than expected
A supermassive black hole in the center of a galaxy typically represents ____ of the galaxy’s total
mass.
A tiny fraction of a percent
The mass of visible matter in a galaxy can be estimated by measuring its luminosity. When this is
compared with the measured mass of the galaxy, astronomers find that ____.
the measured mass is about ten times the estimated mass, due to the effects of dark matter
The mass of a galaxy’s central black hole is related to the mass of the galactic bulge. This implies that
____
central black holes formed when the galaxy bulges forme
Hot, low-density gas can be detected in galactic clusters through X-ray emission. The gas is important
in understanding dark matter because ____
dark matter must make the cluster massive enough to hold on to the hot gas
Gravitational lensing is caused by ____.
bending of light rays due to the curvature of space-time around a mass
Rich galactic clusters are ____
mostly elliptical galaxies
Spiral galaxies are mostly found ____.
in poor clusters
Galactic collisions ____
The Milky Way and other spiral galaxies ____.
. Spiral structures and steady star formation depend on ____.
gentle gravitational interactions with other galaxies
One of the rare galaxies that is isolated in space is likely to be a(n) ____.
flocculent spiral galaxy
At the longest look-back times, we see ____
redshifted irregular galaxies
S0 galaxies have spiral arms, but little to no gas and dust. This is believed to happen because ____.
gas and dust have been stripped from the galaxies as they pass through hot, intergalactic
gas
A galaxy with randomly oriented elongated star orbits and little gas and dust would be a(n)
_______________ galaxy.
elliptical
_______________ galaxies have star formation, but no clear shape
irregular
Because the Hubble constant has a value of 70 km/s/Mpc, a galaxy 50 Mpc away would have a
recession velocity of _______________ km/s. (Round your answer to the nearest 1 km/s).
3500
Because the Hubble constant has a value of 70 km/s/Mpc, a galaxy 50 Mpc away would have a
recession velocity of _______________ km/s. (Round your answer to the nearest 1 km/s).
3500
Because the Hubble constant has a value of 70 km/s/Mpc, a galaxy with a recession velocity of 21,000
km/s must be _______________ Mpc from Earth. (Express your answer as a whole number of Mpc)
300
_______________ are objects of known luminosity used for finding distances
standard candles
. The _______________ time is the amount of time it took light to travel from a celestial object to
Earth.
light travel time
. The mass of a galaxy can be determined from its _______________ curve
rotation
The mass of a galaxy’s central black hole is proportional to the mass of its _______________
host galaxy
The velocity dispersion method can be used to find the _______________ of a galaxy
mass
Galactic _______________ describes the process of a large galaxy absorbing a smaller one
collision
Gravitational _______________ can be used to detect dark matter
Lensing
A galaxy that has created a large number of young stars all at once is a(n) _______________ galaxy.
starburst
A galaxy that has gone through many collisions and mergers must be a(n) _______________ galaxy.
elliptical
Gentle tidal interactions are probably necessary to support the formation of _______________ in a
galaxy
spiral arms
All of the farthest detectable galaxies are _______________ galaxies
irregular
Briefly describe the characteristics of an elliptical galaxy
Elliptical galaxies have a smooth ellipsoidal or spherical appearance, and they have far less structure than spiral galaxies do. Elliptical galaxies are typically found in galaxy clusters.
How are standard candles used to measure distance?
If you have two stars of the same type, but one is further away than the other, it looks fainter. Knowing that they should be the same brightness allows us to work out the distances between them.
Is dark matter important in other galaxies and galactic clusters
yes because they reside in a region where such matter is much denser than average. Scientists believe that the heavier a cluster is, the more dark matter it has in its environment
milkly way compared to others
larger and brighter than most spirals
What is galactic cannibalism?
occurs when the gravitational forces from a larger galaxy or group of galaxies slowly tear apart a smaller galaxy. Characteristic features of galactic cannibalism are streams or halos of stars orbiting the larger galaxy, like the halo of red stars seen around NGC 7317
