AST 3

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Terms in this set (...)

What is nuclear fusion?
two nuclei sticking together to form a new, heavier nucleus
Thermonuclear fusion reactions in the core of the Sun convert four hydrogen nuclei
into one helium nucleus. The helium nucleus has
less mass than the four hydrogen nuclei, the lost mass becoming energy in an amount given by E = mc2
How much longer can the Sun continue to generate energy by nuclear reactions in its
core?
about 5 billion years
What happens to the positrons produced by the nuclear reactions in the core of the Sun?
What happens to the positrons produced by the nuclear reactions in the core of the Sun?
The phrase "hydrostatic equilibrium" in the Sun refers to
the balance of gravity inward and gas pressure outward.
Where is the Sun's energy generated?
the core
Energy is transported from the center of the Sun to the surface
mostly by radiation but with convection in the outer layers.
From the center outward, the order of the layers or parts of the Sun is
radiative zone, convection zone, photosphere, chromosphere, corona
The temperature of the Sun throughout its radius and including its atmosphere
decreases outward from the center, but then increases again.
10. The core of the Sun, in which all the Sun's thermonuclear energy is produced, takes
up about
1/4 of the Sun's radius.
11. A neutrino produced in the nuclear furnace in the core of the Sun
can penetrate easily through both the gas of the Sun's interior and the solid Earth.
12. Which part of the Sun is the origin of most of the light we see?
the photosphere
13. The granulation which is observed on the photosphere of the Sun appears to be the
result of
convection currents
14. The center of the disk of the visible Sun appears brighter than its edges because
we see into deeper and hotter layers at the center of the disk
15. The appearance of the visible spectrum of the Sun, when its light is separated in its
component colors, is
a continuous bright spectrum, crossed by thousands of dark absorption lines.
16. The word "chromosphere" refers to
a layer in the Sun's atmosphere
17. What is a spicule on the Sun?
a jet of rising gas in the chromosphere
18. The bright X-ray image that one obtains of the solar corona when the Sun is
photographed at this wavelength indicates that the gas temperature at these heights
is
extremely high, above 106 K
19. What is the source of the solar wind?
gas escaping through coronal holes
20. Where on the Sun do sunspots occur?
the photosphere
21. What is the average length of time from one maximum in the number of sunspots on
the Sun to the next maximum?
11 years
22. Sunspots are caused by
differential rotation and its effect on weak magnetic fields.
23. The Zeeman effect describes the shift in specific wavelengths of light caused by
magnetic fields acting on the radiating atoms
24. Solar flares occur at what positions on the solar disk?
) only within sunspot groups
25. What appears to be the source of the energy in coronal mass ejections?
magnetic reconnection
Parallax of a nearby star is used to estimate its
distance from Earth
Light, leaving a point source, spreads out so that the apparent brightness, b , of light per unit area varies with distance d according to which law ( means "proportional to")?
b 1/d2.
Suppose that, at night, the brightness of a light bulb is measured from a certain distance and then the light bulb is moved to a distance twice as far away. How bright will the light appear compared to the earlier measurement?
1/4 as bright
Which of the following statements is true of the population of stars in our neighborhood
There are many more faint than bright stars
The luminosity of a star is
the total energy emitted at all wavelengths into all space from its whole surface
Apparent magnitude is a measure of the
brightness of a star, as seen from Earth.
At what distance are stars assumed to be from Earth when they are represented by their absolute (as opposed to their apparent) magnitude?
10 parsecs
The technique called photometry in stellar astronomy is the measurement of
the intensity of light from stars through several limited-bandpass filters from which surface temperature, variability, luminosity, etc. of stars can be determined.
The star Bellatrix in Orion looks bluish to the naked eye. Why is this?
The spectrum of light emitted from Bellatrix peaks in the ultraviolet region of the spectrum. Within the visible part of the spectrum, there is more emission in the blue than in any other color.
The spectrum of an ordinary main sequence star is a
continuum of colors crossed by dark absorption lines, caused by absorption of cooler atoms and molecules at the surface.
From which feature of light from a nearby star is the surface temperature determined most precisely?
relative strengths of absorption lines from different atoms (e.g., H, Ca) and molecules (e.g., TiO)
The spectral type of a star is most directly related to (and determines uniquely) its
surface temperature
In the spectral sequence of star types, each category has been divided into ten intervals. The Sun is classified as
In the spectral sequence of star types, each category has been divided into ten intervals. The Sun is classified as
The relationship between the luminosity of a star, L, its surface temperature, T, and its radius, R, is given (with = Stefan-Boltzmann constant) by
L = 4 R2T 4
Where are brown dwarfs located on the HR diagram?
lower right
Where on the Hertzsprung-Russell diagram do most local stars in our universe congregate?
on the main sequence where stars are generating energy by fusion reactions
What is the physical reason that astronomers can find the luminosity class (I, II, III, IV, or V) of a star using the star's spectrum?
The absorption lines in the spectrum are affected by the density and pressure of the star's atmosphere.
Using the Hertzsprung-Russell diagram in Fig. 17-15a of Freedman and Kaufmann, Universe, 8th ed., determine which type of star has the following characteristics: surface tem of 40,000 K and luminosity 100,000 times that of the Sun.
blue main sequence star
The star Elnath is classified as B7 III, and the star Al Na'ir is classified as B7 IV. This tells us that compared to Al Na'ir, Elnath is
about the same temperature, but intrinsically much brighter
What proportion of visible stars in the night sky are multiple-star systems?
about 50%, or 1/2
Which important stellar parameter can be determined by the study of binary stars?
stellar masses
How do two unequal mass stars move around each other in a binary system?
in elliptical orbits, about a common "center of mass"
An important aspect of binary star systems, as distinct from single stars, is that they allow a
measurement of the masses of stars
The relationship between mass and luminosity of stars on the main sequence is that
the greater the stellar mass, the larger the luminosity
An eclipsing binary system is
two stars that periodically eclipse each other.
The total lifespan of the Sun is believed to be
12 billion years
The predominant color of an emission nebula is
red, from the hydrogen Balmer H line.
The effect of interstellar dust on starlight is
) to dim and redden distant stars by preferentially scattering their blue light
New stars are formed
in huge, cool dust and gas clouds
Protostars are
very young objects, still contracting before becoming true stars.
A star's evolutionary track is
its movement when plotted on a Hertzsprung-Russell diagram, as it evolves in luminosity and temperature.
Suppose that an astronomical observatory announces the discovery of an object with about 50 times the mass of Jupiter, a mass too low to become a main sequence star. What name would the observatory apply to this object?
brown dwarf
What is believed to be the maximum mass that a star can have?
about 200 solar masses
What is the relationship between stellar mass and position on the main sequence of the Hertzsprung-Russell diagram?
The more massive the star, the higher up on the main sequence the star will appear.
What is the relationship between the mass of a protostar and the time needed for it to reach the main sequence, after it forms inside an interstellar cloud?
More massive protostars reach the main sequence in a shorter time than less massive protostars
In the Hertzsprung-Russell diagram, how does the position of a typical star change while it is at the main-sequence phase of its evolution?
A star does not move on the H-R diagram while it is at this phase of its life.
At what stage of its evolutionary life is the Sun?
main-sequence—middle age
A Herbig-Haro object is
glowing interstellar gas, heated by a high-velocity jet of matter from an evolving star.
The Hubble Space Telescope has photographed disks of gas and dust around young, low-mass stars in the Orion Nebula. It is thought that planets may form from the material in disks such as these. What name has been given to these disks?
proplyds
The stars in an open cluster are useful for studying the early stages of stellar evolution because all the stars in a cluster have the same
age
Which range of electromagnetic radiation is useful for observing new-born protostars within their gas and dust nebulas?
infrared
In which one of the following locations are clumps of gas most likely to be collapsing to form stars?
In which one of the following locations are clumps of gas most likely to be collapsing to form stars?
Astronomers use millimeter wavelength radiation to find giant molecular clouds. What is the source of this millimeter radiation?
rotational energy changes in the CO molecule
How can an O-type star trigger the formation of other stars? Three of the following statements are correct, and one is incorrect. Which is incorrect?
O-type stars are massive. When they form stellar nebulae, as the Sun did, small stars form instead of planets.
There are several mechanisms that can trigger star formation in a cold, dark nebula. In each of these the key to star formation is
to compress the gas and dust so that gravitation will overcome the gas pressure.
Through nuclear reactions in their cores, stars on the main sequence convert
hydrogen to helium
The total time the Sun will spend as a main-sequence star is
about 10 billion years
How is the length of a star's lifetime related to the mass of the star?
Higher-mass stars run through their lives faster and have shorter lifetimes.
The event which marks the end of the main sequence lifetime of a star is
The event which marks the end of the main sequence lifetime of a star is
What is the next stage in a star's life after the main-sequence phase?
red giant
After a star becomes a red giant, hydrogen fusion
occurs in a shell around the core.
The majority of the elements heavier than hydrogen and helium in the universe are believed to have originated in
the central cores of stars
Why does it require higher gas temperatures in the core of a star to produce nuclear fusion of helium compared to that required for hydrogen?
Higher collision speeds are needed to overcome the extra electrostatic repulsion between doubly charged He nuclei.
Electron degeneracy, a result of the Pauli exclusion principle that prevents electrons from becoming crowded together beyond a certain limit, is important in
the core of a low-mass star just before the start of core helium burning.
The helium flash is another name for
a sudden onset of helium fusion reactions in the core of a low-mass red giant star.
Which way does a star of about 1 solar mass evolve, on the Hertzsprung-Russell diagram, at the end of its main-sequence lifetime?
toward higher luminosity and lower temperature—away from the main sequence
Horizontal-branch stars, which have a range of temperatures with luminosities between 50 and 100 times that of the Sun, are in what stage of their lives?
core helium burning
What are the main general features that make clusters of stars useful to astronomers?
The stars are at the same distance from Earth, were formed at approximately the same time, and were made from same chemical mix.
The age of a cluster can be found by
determining the turnoff point on the main sequence of its HR diagram.
Which of the following stars are metal-poor?
population II stars
What kind of star is our Sun?
metal rich Population I
Cepheid stars are
stars that pulsate in brightness, size, and temperature.
RR Lyrae stars are
pulsating stars that vary regularly, all with periods of less than one day.
The shape of the cross-section of the Roche lobes around a close binary star system, taken through the centers of the stars, is
a figure-eight
. Which factor, more than any other, modifies the evolutionary tracks of stars in binary combinations compared to their single star counterparts?
mass exchange between the stars
When does the Helium Flash occur?
when helium fusion begins in a low mass star
In terms of a star's evolutionary life, an asymptotic giant branch (AGB) star is in the
helium shell-burning phase
A planetary nebula is
the atmosphere of a red giant star slowly expanding away from the star's core to form a shell of gas.
The final remnant of the evolution of a red giant star that has ejected a planetary nebula is a
white dwarf star
A white dwarf star is about the same size as
the Earth
The energy generation process inside a white dwarf star is
nonexistent; a white dwarf star is simply cooling by radiating its original heat.
The stars that eventually become white dwarfs are those that start life with masses of less than about
4 solar masses
White dwarf stars of different masses have radii or sizes for which
the more massive the star, the smaller it is.
As a white dwarf evolves, the direction of its motion on the Herzsprung-Russell diagram below the main sequence is upper right to lower left, which means that
its size or radius remains constant as it cools and becomes less luminous.
There is a mass limit for a star in the white dwarf phase, the Chandrasekhar limit, beyond which the star can no longer support its own weight. This mass limit, in terms of solar mass, is
1.4
A sequence of thermonuclear fusion processes inside massive stars can continue to transform the nuclei of elements such as carbon, oxygen, etc. into heavier nuclei and also generate excess energy, up to a limit beyond which no further energy-producing reactions can occur. The element that is produced when this limit is reached is
iron
The core collapse phase at the end of the life of a massive star is triggered when
nuclear fusion has produced a significant amount of iron in its core
What is photodisintegration?
splitting apart of atomic nuclei by high-energy gamma rays
What is the source of most of the heavy elements on the Earth and in our own bodies?
explosive nucleosynthesis during supernova explosions of massive stars
The neutrino is
an elusive subatomic particle, having very little or no mass and difficult to detect.
What is Cerenkov radiation?
the shock wave emitted when recoil positrons move faster than the speed of light in water
Can a white dwarf explode?
Yes, but only if it is in a binary star system.
A Type II supernova is the
explosion of a single massive star after silicon burning has produced a core of iron nuclei.
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.
When a supernova explosion results from core collapse in a massive star it appears to leave behind
a rapidly expanding shell of gas and a central neutron star or black hole.