CHAPTER 19 PRACTICE
Terms in this set (50)
True Or False? A stage 4 protostar may temporarily be thousands of times more luminous than the Sun.
True Or False? Collisions between galaxies tend to destroy, not create, stars.
True Or False? Stars evolve to the upper left along the main sequence, after forming in the middle.
True Or False? If a star is spinning rapidly, this may limit its final mass
True Or False? Many of the brightest stars we see are only a few million years old.
True Or False? Brown dwarfs most commonly form in the nebular disk around another object, much like a planet.
True Or False? Rotation and magnetism both play key roles in protostar formation.
True Or False? It takes about 1032 hydrogen atoms to make a star.
True Or False? Shock waves from supernovae disrupt an interstellar cloud and prevent it from forming stars.
True Or False? A protostar of 20 solar masses should form a star that will stay on the main sequence twenty times
longer than our Sun.
Higher mass protostars enter the main sequence:
faster and at a higher luminosity and temperature.
Objects which have contracted, but are of too little mass to establish thermonuclear
reactions in their cores, are ________, which slowly continue to cool.
In general, the greater the mass of the protostar, the ________ it contracts to the main
More massive stars are able to form in a(n) ________ time than less massive stars.
After stage 3 in star formation, the protostar develops a surface better known as a(n)
To deduce the interior conditions of the dense regions in which stars form, it is necessary
for astronomers to observe in the ________ part of the spectrum.
The Great Explosion of Eta Carinae expelled about ________ solar masses of material and
released about as much visible energy as a supernova.
2 or two
Star formation may be triggered by ________ which aid gravity through compression of
interstellar clouds to greater densities
pressure or shock waves (from supernovae)
During the Kelvin-Helmholtz contraction phase, a protostar has a much ________
brightness as compared to the Sun.
The Orion Nebula and Tarantula Nebula are examples of ________ Nurseries.
A protostar develops a bipolar flow of gas when it is still surrounded by an equatorial disk
From stage 4 to stage 7 of star formation, the object plotted on the H-R diagram moves so that:
its luminosity decreases, while its temperature increases.
The stars found in nebulae like the Orion Nebula probably formed:
a few million years ago
Atomic bomb tests demonstrated which aspect of star formation?
a shock wave surrounding and compressing a molecular cloud
Protostars can be observed in:
the Orion Nebula.
Most open clusters in our Milky Way are about how old?
less than a billion years old
As a star forms, the photosphere first appears:
when the protostar forms.
Which relationship concerning the mass of protostars is FALSE?
A) The more massive ones create a lot of ultraviolet as well as visible light.
B) The more massive ones will reach the main sequence first.
C) The more massive ones will be the hottest and most luminous.
D) The more massive ones are so luminous they ionize the gas, hence red H II regions.
E) The more massive ones will be made of the heaviest elements.
The more massive ones will be made of the heaviest elements
If the initial interstellar cloud in star formation has a mass sufficient to form hundreds of stars, how
does a single star form from it?
The cloud fragments into smaller clouds and forms many stars at one time.
Which of these is NOT a source of the shock waves that lead to protostars?
expanding Herbig-Haro objects
What is characteristic of a main sequence star?
The rate of nuclear energy generated in the hydrogen to helium fusing core equals the rate
radiated from the surface.
Our Sun, along with most of the stars in our neighborhood, probably formed:
billions of years ago.
Whether an object is a brown dwarf or a planet can be determined by:
the composition of the object.
How long does it take for a star like our Sun to form?
fifty million years
The most important fact about a cluster of stars that makes them useful for studying star formation
all the stars formed at about the same time
What are some complications that interfere with star formation?
A rapidly spinning nebula may prevent more matter from collapsing to the central protostar, and magnetic fields may
deflect the gas away from the star as well.
What are thought to be some possible causes of triggering the contraction of an interstellar cloud?
The shockwave from the formation of nearby type O and B stars, the shockwave from a nearby supernova, or parts of
the cloud become too cold to balance the inward force of gravity.
A typical protostar may be several thousand times more luminous than our Sun. Where does this energy come fr
From the release of gravitational energy as the protostar shrinks in stages 2 and 3.
Explain how the composition of the object can help distinguish a brown dwarf from a planet.
Planets are enriched in heavy elements compared to the host star; brown dwarfs should have starlike composition.
Explain how rotation and magnetic fields influence the formation of the protostar.
Rotation flattens the dusty cocoon into a disk around the protostar's equator, and the magnetic fields guide bipolar
flows of material outward to make Herbig-Haro objects.
Contrast the brightest stars of young open and old globular clusters.
Hot blue main sequence stars light up young open clusters, but the aging globular clusters have long since lost such
short-lived massive stars; they have red giants as their brightest, most evolved survivors.
Why does gravitational contraction halt in collapsing protostars?
Gravitational contraction heats up the protostar in stages 2-4, but once the star has heated up enough, its radiation
pressure stabilizes it as nuclear fusion ignites
What do we mean by the term "molecular clouds"? Why do they exist? How can observation of their properties yield
clues to the processes of stellar formation?
Molecular clouds are very cool interstellar gas clouds; cool enough that complex molecules can form. A shock wave,
from an emission nebula or an exploding star, can lead to star formation in the molecular cloud.
An interstellar gas cloud has the mass to form hundreds of stars. What generally happens to it?
The cloud fragments into smaller clouds and forms many stars.
What stage of star formation is ZAMS?
At stage 7, the zero age main sequence star is fusing hydrogen and on the main sequence, to stay there for as long as it
has sufficient hydrogen to remain stable.
Why does a star's luminosity drop so much during the Hayashi track?
The surface of the star maintains a fairly constant temperature but the size continues to shrink significantly. Since the
luminosity depends on the square of the radius, as the radius decreases by a factor of 100, the luminosity drops by a
factor of 10,000. The slight increase in surface temperature changes the luminosity only a little.
Discuss the relationship between young stars and the interstellar medium.
Young stars give off ultraviolet radiation, heating the surrounding gas cloud and causing it to glow as an emission
nebula. Solar wind from the young stars pushes on the nebula, which can sweep away the gas, but can also cause
compression leading to more new star formation.
What are some sources of the shock waves that initiate star formation?
Emission nebulae produce shock waves, resulting from their hot ionized gases. Supernovae are an excellent source of
shock waves. Both of these are caused by O-B stars. Collisions between galaxies can also initiate star formation on a
grand scale in "starburst" galaxies.
Outline the process of star formation, including all relevant factors that influence the outcome.
An interstellar cloud, disturbed in some way, begins to gravitationally collapse. It heats up as it collapses, and spins
faster. (If the spinning is too great it may defeat the entire process, as the protostar tears itself apart.) Eventually the
core of the cloud is hot enough that it develops a definite glowing edge (photosphere), and begins to resemble a star.
When the core temperature reaches 10 million K and nuclear fusion of hydrogen into helium begins, it is officially a
star. When the outward pressure equalizes with gravity, the star enters the main sequence. Collisions between galaxies
can set up a shock wave to initiate collapse, as can the shock waves from supernovae and the density wave moving
through the spiral arms of the galaxy.
What factors can complicate the collapse of an interstellar cloud into a star?
The initial spin of the cloud and the conservation of angular momentum result in the cloud flattening into a rapidly
rotating disk. For the disk not to fly apart requires a larger mass to produce sufficiently strong gravity to hold the disk
together. Magnetic fields can hinder the collapse in a direction perpendicular to the field lines. The ionized gas is tied
to the magnetic field and the field is pulled in by the gas. The ionized gas responds more to the magnetic field than it
does to gravity.
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