astronomy- chapter 15 quiz review
The average density of the interstellar medium is:
1 atom/cm3
A typical molecular cloud has a temperature of approximately:
10 K
Dust that is heated to 30 K will emit a blackbody spectrum that peaks at:
100 ym
The figures below show the spectrum of a star, along with five other spectra labeled A through E. Which one of the labeled spectra shows what the spectrum of that star would look like if it were viewed through a significant amount of interstellar dust?
D
Below are three pictures of the disk of the Milky Way, taken in three different wavelength ranges. Put the three pictures in order from shortest to longest wavelength.
II, III, I
What critical event transforms a protostar into a normal main-sequence star?
Nuclear fusion begins in the core.
An H II region signals the presence of:
all of the above
If you wanted to study regions where star formation is currently happening you could use:
all of the above
In the interstellar medium, molecules survive only in regions with:
all of the above
Molecular cloud cores are places where you might find:
all of the above
Where have astronomers observed the existence of planets?
all of the above
What happens as a protostar contracts?
all of the above are true
Sitting in a 100 degree hot tub feels much hotter than standing outside on a 100 degree day. This analogy illustrates why:
an astronaut would feel cold standing in the 10^6 K intercloud gas
An accretion disk forms around a collapsing protostar because infalling material must conserve:
angular momentum
A ___ is a failed star that shines primarily because of energy derived from its gravitational collapse rather than nuclear burning.
brown drawf
"Weather" in the interstellar medium is produced:
by supernovae and strong winds from luminous stars
Stars with a mass from 0.01 M to 0.08 M are very different from the Sun because they:
cannot successfully execute the proton-proton chain reactions
Of the following processes at work in molecular clouds, which is the one that inevitably dominates the clouds' evolution?
conservation of angular momentum
If you wanted to observe heavy elements in the interstellar medium, where would be the best place to look?
dust grains
For an object in hydrostatic equilibrium, if the temperature inside the object were to increase, the object would:
expand
When looking at the space between stars, what might you see?
gas
The source of energy for a contracting protostar comes from:
gravitational potential energy
If you could watch stars forming out of a gas cloud, which stars would form first?
high-mass stars
Brown dwarfs are considered failed stars because:
hydrogen fusion never begins in their cores
As a protostar evolves, its temperature:
increases due to the kinetic energy of infalling material
Magnetic fields inside a molecular cloud act to:
inhibit gravitational collapse
The red emission in the photo below is due to:
ionized hydrogen (H II region)
21-cm radiation is important because:
it allows us to study neutral hydrogen in the interstellar medium
What is the most likely explanation for the dark area in the image below?
it is a region with thick dust blocking the starlight coming from behind.
The most common types of stars in our galaxy are:
low-mass stars
Use Figure 1 to compete the following statement. A high-mass protostar remains roughly constant in ___ and increases in ___ as it follows its evolutionary track.
luminosity; temperature
A surprising fact about a 1 M protostar is that, even though nuclear reactions have not yet started in their cores, they are ___ than the Sun.
more luminous
Molecular clouds, which have temperatures of around 10 K, are best observed at ___ wavelengths.
radio
Warm ionized gas in the interstellar medium appears ___ when imaged in the optical region of the electromagnetic spectrum.
red
Interstellar clouds are:
regions where hydrogen tends to be denser than the surrounding gas
Because angular momentum must be conserved, as a gas cloud contracts due to gravity it will also:
spin faster
Use Figure 1 to complete the following statement. A low-mass protostar remains roughly constant in ___ and decreases in ___ as it follows its evolutionary track.
temperature; luminosity
When radiation from an object passes through the interstellar medium:
the object appears redder and dimmer
We detect neutral gas in the interstellar medium by looking for radiation at 21 cm that arises when:
the spin of an electron flips and aligns with the spin of a proton in a hydrogen atom