Astronomy Chapter 20-21
A typical molecular cloud has a temperature of approximately
10K
The coldest molecular clouds in our galaxy have temperatures of approximately
10K
What is the most likely explanation for the dark area in the figure shown?
It is a region with thick dust blocking the starlight coming from behind.
What happens as a protostar contracts?
Its density rises, Its temperature rises, Its radius decrease, Its pressure rises. (all of the above)
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
Sitting in a 100°F hot tub feels much hotter than standing outside on a 100°F day. This analogy illustrates why
an astronaut would feel cold standing in the 10⁶ 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 dwarf
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
Which of the following traits does not help slow or prevent the collapse of a gas cloud?
high mass
If you could watch stars forming out of a gas cloud, which stars would form first?
high-mass stars
. A protostar's evolutionary "track" in the H-R diagram traces out
how the protostar's luminosity, temperature, and radius change with time.
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.
Dust in the ISM appears dark in _________ wavelengths and bright in _________ wavelengths.
infrared, visible
Magnetic fields inside a molecular cloud act to
inhibit gravitational collapse.
The most common types of stars in our galaxy are
low mass stars
Use the figure shown to complete the following statement. A high-mass protostar remains roughly constant in
luminosity, temperature
The average density of the interstellar medium is
much less dense than the best vacuum on Earth.
Dust reddens starlight because it
preferentially affects light at visible and shorter wavelengths.
The entire process of star formation is really just an evolving balance between
pressure and gravity.
Molecular cloud cores are places where you might find
protostars, Herbig-Haro objects, molecular hydrogen (H2), carbon monoxide (CO). (all of the above)
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 the figure shown 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.
The dust in the interstellar medium comes primarily from
the stellar winds of main-sequence stars
What primarily makes it difficult to observe the process of star formation?
they occur in dusty regions
