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
