ASTR FINAL
What is the lowest mass an object can have and still be a star?
0.08 solar mass
What is the typical temperature inside the dense core of a giant molecular cloud that is collapsing to form a star?
10 K
The characteristics of a red supergiant star are the brightness of _____ and a diameter of _____.
10,000 Suns; about Mars's orbit
What is a typical size for a giant molecular cloud?
100 ly across
What is the typical mass of a giant molecular cloud?
100,000 to 1 million solar masses
How long will the Sun have spent as a main-sequence star when it finally begins to evolve toward the red giant phase?
1010 years
How much brighter than its main-sequence luminosity will a Sun-like star become at the asymptotic giant branch (AGB) phase of its life?
104 times brighter
When a typical nova explodes, it brightens in a few hours by a factor of
104 to 106.
What are the stars in the upper part of the instability strip called?
Cepheid variables
What does the term hydrostatic equilibrium mean in reference to stars?
Each layer within a star is in balance with respect to pressure and gravity.
Low-mass stars can ascend the H-R diagram in two evolutionary phases called giant phases. What is the difference between them?
In the first, the primary production of energy is from hydrogen burning in a shell around the core. In the second, the primary production of energy is from helium burning in a shell around the core.
A white dwarf star, as it evolves, undergoes which of the following changes?
Luminosity and temperature decrease.
How do massive stars normally end their lives?
Massive stars explode.
If you were able to visit Earth one million years into the future, which of the following views of the sky would be most likely?
Nearby stars would have moved in position and some stars that are presently blue would have changed color, but otherwise the sky would be very much as it is now since 1 million years is a very short time in astronomical terms.
What event occurs at the end of the protostar stage of a star's life?
Nuclear reactions begin in the star's core, converting hydrogen into helium.
What are the stars in the lower part of the instability strip called?
RR Lyrae variables
What is the most important process that causes a protostar to stop accreting mass?
Radiation and particles from the hot protostar push infalling matter away from the protostar.
Why do H II regions glow?
Some H II ions unite with electrons to re-form neutral hydrogen. In this process, the electron passes from level to level in the atom and emits a cascade of photons.
The end of the life of a red dwarf star is predicted to be a sphere of almost pure helium. But no such spheres have been detected. What do we believe is the reason?
The evolution rate for red dwarfs is so slow that none has yet evolved to its end stage.
What makes a red giant star so large?
The hydrogen-burning shell is heating the envelope and making it expand.
In a Cepheid variable, what happens to make the temperature decrease?
The ionized helium layer expands and cools.
What is the ultimate fate of an open star cluster?
The stars in the cluster escape one by one until the cluster no longer exists.
How is it that white dwarfs, which are relatively small, can have surface temperatures of several tens of thousands of Kelvins?
The surface of the white dwarf is actually the core since the cooler outer layers have been blown off.
Brown dwarfs and Jovian planets have many similarities. In which of the following aspects are they not similar?
They are fully convective at various stages.
Can a white dwarf explode?
Yes, but only if it is in a binary star system.
Which one of the following objects is the least massive?
a brown dwarf
The diameter of a typical planetary nebula, after 10,000 years of expansion, is
a few light-years.
Accretion of matter in an interstellar cloud leads to
a protostar.
A low-mass red dwarf (0.08 M < M < 0.4 M) will eventually not become
a red giant, a brown dwarf, or a white dwarf.
How many stars are there in a large globular cluster?
about 1 million
What is believed to be the maximum mass a star can have?
about 150 solar masses
How large was the Sun when it first formed as a protostar?
about 5 times its present diameter
At what stage in its life does a star pass through the protostar phase?
after condensation but before nuclear reactions begin in its core
Which of the following common molecules found in interstellar space contains nitrogen atoms but no oxygen?
ammonia (NH3)
What determines whether a particular region of an interstellar cloud can collapse and form a star?
amount of gravity pulling inward compared with gas pressure pushing outward
What percentage of all matter ejected into the interstellar medium in the Milky Way Galaxy each year by stars is contributed by planetary nebulae?
between 10 and 20%
For an amateur astronomer to observe some of the more visible nebulae, it is suggested that the instrument to be used is
binoculars because they have a larger field of view and can allow the whole nebula to be seen.
What is the name given to the type of planetary nebula in which a doughnut-shaped cloud of gas and dust in the plane of the equator channels the outflow in opposite directions toward the poles?
bipolar planetary nebula
What is the characteristic color of a reflection nebula?
blue
A reflection nebula is made visible by
blue light preferentially scattered by dust grains.
What are the main products of helium nuclear fusion in red giant stars?
carbon and oxygen nuclei
There are several mechanisms that can trigger star formation in a cold, dark nebula. In each mechanism, the key to star formation is
compressing the gas and dust so that gravitation will overcome the gas pressure.
Protostars are slowly
contracting and heating up.
A Type Ia supernova is the
explosion of a white dwarf in a binary star system after mass has been transferred onto it from its companion.
What is the last nuclear fusion stage in the life of a low-mass star like the Sun?
fusion of helium nuclei to form carbon and oxygen
The space between stars is known to contain
gas, both atomic and molecular, and dust.
All stars on the main sequence
generate energy by hydrogen fusion in their centers.
Star formation takes place in
giant molecular clouds.
The source of a protostar's heat is
gravitational energy released as the star contracts.
What is the second most abundant element in the universe (after hydrogen)?
helium
What is a Cepheid variable star?
high-mass star that pulsates regularly in brightness
New stars are formed from
huge, cool dust and gas clouds.
What is the most abundant element in the universe?
hydrogen
Where in the universe would you look for a protostar?
in dense dust and gas clouds
The definition of a main-sequence star is a star
in which nuclear fusion reactions generate sufficient energy to oppose further condensation of the star.
If you were to look for a protostar in its early stages, you would observe in which wavelength region?
infrared
The Orion Nebula is a
large interstellar gas and dust cloud containing young stars.
A brown dwarf is a(n)
object intermediate between a planet and a star, with not enough mass to begin nuclear reactions in its core.
The Jeans instability describes the
overcoming of gas pressure, by self-gravity in a cold and dense interstellar cloud, to form a star.
The apparent reddening of light from stars after its passage through the interstellar medium (ISM) is caused by
preferential scattering of blue starlight by fine dust grains.
A T Tauri star is at what stage of its stellar evolution?
protostar, before the main-sequence phase
RR Lyrae stars are
pulsating stars that vary regularly, all with periods of less than one day.
Which type of dwarf is largest?
red dwarf
A star on the asymptotic giant branch (AGB) is a
red supergiant.
Which part of the Hertzsprung-Russell diagram is occupied by protostars?
right of the main sequence
A planetary nebula is a
shell of gases ejected from the surface of red giant star.
A white dwarf is a(n)
small, very hot, low-mass star.
What is a protostar? 0
sphere of gas after collapse from an interstellar cloud but before nuclear reactions have begun
The T Tauri phase of a protostar is characterized by
strong spectral emission lines.
The Cygnus Loop nebula is characterized by having an arched appearance. The Cygnus Loop is a
supernova remnant.
The next stage in a star's life after the main-sequence phase is
the red giant phase.
Planetary nebulae are so named because
they were extended objects, often green-colored, that looked like planets when first seen by nineteenth-century observers through their telescopes.
A white dwarf star is at what stage of its evolution?
very late phase of evolution, no longer generating energy
In astronomical terms, planetary nebulae are
very short-lived, with lifetimes of about 50,000 years.
When does a star achieve static equilibrium?
when it becomes a main-sequence star
At what point in its evolution does a protostar stop shrinking and stabilize into a star?
when nuclear processes generate enough energy and internal pressure to resist gravitational contraction
The final remnant of the evolution of a red giant star that has ejected a planetary nebula is a
white dwarf star.
What is a T Tauri star?
young G, K, or M star that is ejecting gas
The bright stars at the center of an emission nebula (H II region) are
young O stars and B stars.