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Stellar Evolution
Can You Answer the Following
Questions?
ATOMS
1. The smallest quantity of matter which retains the chemical properties
of that material is
called an _______________.
2. An atom is composed of three basic subatomic particles. They are
called the
_______________, _______________, and the _______________.
3. Both the protons and the neutrons are located in the center of
the atom which is called the
_______________.
4. _______________ orbit the nucleus of an atom, but are not attracted
to it by the force of
gravity.
5. Rather, protons have a _______________ charge and electrons have
a
_______________ charge. This difference in electrostatic
charges, called the
electromagnetic force holds the atom together.
6. In matter which is neutral, atoms or molecules contain an _______________
number of
electrons and protons.
7. Atoms or molecules are not balanced with respect to the number
of proton or electrons
which they contain when matter is _______________.
These atoms or molecules are
now called _______________.
8. When ions and electrons are mixed together, they are called a _______________.
The physical state of this material is a SOLID,
LIQUID, GAS (circle one). The
temperature is HOT/COLD (circle one).
9. E___________ absorbed by the electron is one way in which
it can become detached
from the nucleus. An atom or molecule which
loses an electron is said to be
_______________.
ENERGY
10. The whole array of different energies, of which light is just
one component, is called the
_______________ spectrum.
11. The different components of this energy spectrum, in their correct
order from the most
intense to the least intense are as follows:
_______________ less than 1 Angstrom (Å)
in length
_______________ 1 to 100 Å in length
_______________ 100 to 4000 Å in length
Visible Light _____ 4000 to 7000 Å
in length
_______________ 7000 A to 1 mm in length
_______________ 1 mm to 1 meter in length
_______________ greater than 1 meter
One Angstrom equals 0.00000001 cm or 10-8 cm. Another way of describing
the
smallness of an Angstrom is to say that there are 254,000,000 or 2.54
x 108 Å/inch .
12. All forms of electromagnetic energy travel at the speed of _______________.
13. Electromagnetic energy can be described as a _______________ or
a
_______________. Each description helps us to
visualize certain characteristics of this
energy as it applies to its encounters with
matter.
14. For example, if energy knocks an electron of an atom out of orbit,
it is best imagined the
energy to be in the form or a _______________.
Synonyms for this description might
be a photon, quanta, or energy packet.
15. However, if a person is describing the size of the electromagnetic
energy, the description
of a _______________ might be more appropriate.
THE ELECTROMAGNETIC SPECTRUM
16. When electromagnetic energy is described as a wave, the distance
between wave crests
is designated as the _______________ of
that radiation.
17. List the following portions of the electromagnetic spectrum, given
below, in correct order
with respect to wavelength, proceeding from
longest to shortest.
visible, infrared, gamma rays, x-rays, microwaves,
radio, ultraviolet
_______________ longest...
________________
_______________
_______________
_______________
_______________
_______________ shortest...
18. Since all electromagnetic radiation travels at the velocity of _______________,
the
number of wave crests passing a given point
per second will be HIGHER/LOWER
(circle one) for radiation of a shorter wavelength.
19. The number of wave crests passing a given point per second is
termed the
_______________ of the radiation.
20. Give the name of a portion of the electromagnetic spectrum which
has a high frequency, a
medium frequency, and low frequency.
high _______________, medium _______________,
low _______________
21. The electromagnetic spectrum represents a band of energy of different
intensities. The
shorter the wavelength, the HIGHER/LOWER (circle
one) the energy. The higher the
frequency, the HIGHER/LOWER (circle one) the
energy.
22. The visible spectrum, which represents that portion of the electromagnetic
spectrum
which can be seen by the _______________, contains
the colors which are given by the
famous acronym ROY G. BIV. These colors, in
their correct order from longest to
shortest wavelength are : _______________, _______________,
_______________,
_______________, _______________, _______________,
______________.
23. The color visible to the human eye with the longest wavelength,
_______________, is
the color with the HIGHEST/LOWEST (circle one)
frequency. The color with the shortest
wavelength has the HIGHEST/LOWEST (circle one)
frequency.
24. Multiplying the frequency (f) of the electromagnetic radiation
by a constant, called
Planck's Constant (h = 6.625 x 10-27 erg sec)
yields the actual amount of
_______________ that each frequency will deliver.
The shorter the wavelength, the
MORE/LESS (circle one) energetic the radiation.
THE NATURE OF LIGHT AND MATTER
25. The energy curve for an object which is a perfect absorber and
emitter of energy is
referred to as a _______________ energy distribution.
Stars are basically perfect emitters
and absorbers of energy. Their energy distribution
is very consistent with blackbody
radiation curves.
26. Two stars at different temperatures are emitting energy spectrums
of various wavelengths
of visible and nonvisible light. The star which
is cooler will have its energy distribution
curve shifted towards the RED/BLUE (circle one)
with respect to the hotter star (Wien's
law). At all points along the energy curve,
the hotter star will be radiating MORE/LESS
(circle one) energy than the cooler star. The
temperature of a stars in K = 0.29/dominant
wavelength measured in centimeters.
27. The energy being radiated per unit area at a star's surface is
a direct function of the
_______________ of that star (Stefan-Boltzmann
law).
28. A hotter star will radiate MORE/LESS (circle one) energy at all
wavelengths than a
cooler star. Besides this, the hotter star will
radiate its maximum energy at a
SHORTER/LONGER (circle one) wavelength. Therefore,
the hotter the star, the
BLUER/REDDER (circle one) its light will become.
29. What is found is that stars which are cool, radiate most of their
energy in the
_______________, whereas, stars like our sun,
have their peak radiation areas in the
_______________. Hot stars radiate most of their
energy in the _______________. The
location of the peak of the energy curve, with
respect to the eye? color perception, is why
the temperature of a star can be understood
through a qualitative observation of its
_______________.
30. Knowing the precise energy peak of a star gives astronomer a good
quantitative
measurement of the _______________ of a star;
however, color is difficult to perceive
with just the human eye, because most of the
stars in the sky are very faint. Two of the
best examples for detecting color with the eye,
or with binoculars, are Rigel, the
_______________ (color) star which forms the
right knee of Orion, the hunter, and
Betelgeuse, the _______________ (color) star,
which defines the left shoulder of the
hunter.
31. However, just describing a star's color is a very qualitative method.
The instrument which
allows astronomers to gain a numerical understanding
of a star? color is a
_______________. Such an instrument uses the
light gathered by a telescope and splits it
into its component colors, called a _______________.
The information obtained from the
dispersed light of a star, deals with how the
intensity of light varies as a function of its
wavelength. A diffraction grating, such as ?azar
Shades," can be used to view the spectrum
of fluorescing gases. Fine, closely spaced lines
are used to bend light of different colors
through different angles to produce a spectrum.
32. The solar spectrum peaks at about _______________ Angstroms (Å).
Blue stars like
Rigel peak at LONGER/SHORTER (circle one) wavelengths
than red stars like
Betelgeuse. The solar peak falls about midway
between these two stars.
33. The farther towards the blue the peak of the spectral curve appears,
the
HOTTER/COOLER (circle one) the star becomes.
In fact the precise location of the
spectral peak will determine the exact _______________
of the star.
34. All stars are essentially composed of _______________ and _______________.
Elements which are heavier than the two most
common constituents of the universe, which
were mentioned above, are called _______________.
THREE LAWS OF SPECTROSCOPY
35. A solid, liquid, or gas (under high pressure) when heated and
made to incandesce (glow)
produces a _______________ spectrum--Law I
36. A rarefied gas when made to glow produces bright spectral lines
at wavelengths
distinctive only to that gas. This type of spectrum
is called an _______________
spectrum--Law II
37. A cool, rarefied gas found between a continuous source and an
observer will produce an
_______________ spectrum--Law III
38. The name of the German physicist who formulated the three laws
of spectroscopy
mentioned above was Gustav K_____________
(1824-87).
THE MESSAGE OF STARLIGHT
39. The elements which compose a star can be revealed through the
analysis of that star's
_______________ spectrum. However, the spectra
of various stars appear to emphasize
different elements in their chemical makeup.
This is not so much the result of a variation in
composition between the stars, but rather a
difference in the _______________ of the
various luminaries.
40. The difference in a star's temperature will be revealed by which
particular absorption lines
in the spectrum attain the greatest _______________.
This factor by itself DOES/DOES
NOT (circle one) indicate the quantitative
composition of that star. The differences in the
spectra of the stars has allowed astronomers
to attempt a _______________ system.
41. Because the atoms of "metals" are more complex than
hydrogen and helium, electrons
will be found CLOSER TO/FARTHER FROM (circle
one) the nucleus of the atom. It will
require MORE/LESS (circle one) energy to ionize
a metal than it will a hydrogen or
helium atom. This translates into a HIGHER/LOWER
(circle one) temperature. To break
the bonds between atoms in a molecule requires
MORE/LESS (circle one) energy
(temperature) than to ionize a metal.
42. Very cool stars display the spectral absorption bands (fingerprints)
of
_______________ in their spectra because temperatures
are low enough for atoms to
combine. Warmer stars like the sun display prominent
absorption lines of various
_______________ such as calcium, sodium, and
iron. The hottest stars have spectra
which display prominent lines of _______________
, _______________, and multiple
lines of ionized metals.
43. Classify the spectral types listed below into hot, medium, and
cool temperature regimes.
O B
A
F
G
K M
_____________________, ______________, _______________
44. Write a mnemonic device which will allow you to remember the spectral
classification of
the stars in order of decreasing temperatures.
______________________________________________________________________
45. Neutral helium is labeled He I, while singly ionized He is written
He II. Doubly ionized
calcium is noted as Ca III. Please write the
correct representations for the following elements:
a. Iron (Fe) with nine electrons missing _______________
b. Silicon (Si) with two electrons missing _______________
c. Silicon (Si) with three electrons missing
_______________
d. Neutral hydrogen (H) _______________
46. The greater the ionization of the elements which compose a star's
atmosphere, the
HOTTER/COOLER (circle one) that star will be.
THE BRIGHTNESS OF STARS
47. The scheme for classifying stars according to their brightness,
or _______________,
originated from the ancient _______________.
48. They called the brightest stars _______________ magnitude stars,
while the dimmest stars
were said to be of the _______________ magnitude.
49. Today astronomers have quantified the magnitude system. The key
to its understanding, is
to realize that the brighter the object, the
MORE/LESS (circle one) positive its magnitude,
and that the intensity difference between magnitudes
is equivalent to _______________, not
2.0. The intensity difference between five whole
magnitudes, i.e., from a 1st to a 6th
magnitude star is equal to _______________ times
in intensity.
50. The brightness of a star in the night sky as seen from the earth
is designated by that star's
_______________ magnitude.
51. The brightness and color of stars are two major characteristics
of these objects which can
be measured with a large telescope. The amount
of light gathered by a telescope from a star
depends upon the actual brightness of the luminary
and its _______________ from the
observer.
52. A casual glance into the night sky reveals that some stars appear
to be brighter than other
stars. Just because one star looks brighter
than another does not mean it is giving off more
light. A star might look bright because it is
very _______________ to us, or because it is
exceedingly _______________. If we knew the
_______________ to the star, we could
determine the actual energy output, since we
know that the brightness of a light source varies
as the inverse ______________________________.
53. If the distance to a star is known, then it is possible to mathematically
obtain a
QUALITATIVE/QUANTITATIVE (circle one) measurement
of the actual amount of energy
which the star is emitting. This is known as
a star? _______________ magnitude.
54. The problem has been solved by accurately measuring the P______________
of nearby
stars created by the earth's yearly circuit
around the sun. When the distance to a star is
known, as well as its apparent magnitude, it
is possible to mathematically manipulate its
distance from the earth to see how its brightness
compares with other stars of known
distance. If the brightnesses of many stars
can be compared to each other at a standard
distance, than it will become possible to see
which ones are really the bright luminaries, and
which stars appear bright only because of their
closeness to the earth. The formula for
accomplishing this is m - M = 5 log (d/10),
where m and M are the apparent and absolute
magnitudes respectively, and d is the distance
to the object in parsecs. One parsec equals a
distance of _______________ light years.
55. A star which shifts through a PARallax angle of one SECond of
arc is at a distance of
____________________ from earth.
56. The standard distance to which stars are mathematically moved
for comparison purposes is
equivalent to ____________________. This distance
equals _______________ light years.
This is represented by the 10 in the formula
m - M = 5 log (d/10).
57. The luminosity of a star, standardized for a distance of 10 parsecs
from earth is known as
that star's _______________ magnitude.
58. One might think that stars of every spectral classification would
fall into every category of
absolute magnitude. This is, however, untrue.
Early in the 20th century the Danish
astronomer, Ejnar _______________, and the American,
Henry Norris
_______________, independently combined
the concepts of absolute luminosity (absolute
magnitude) and temperature (spectral classification)
into a graphical analysis for several dozen stars.
Their efforts resulted in the foundation for our modern understanding
of the life cycles
of stars. These two individuals discovered that
stars of a particular spectral classification
could only possess a specific luminosity. In
other words, a star's spectral classification
predestined its _______________ magnitude. Color-luminosity
plots of stars are collectively known as Hertzsprung-Russell
diagrams, also abbreviated as _______________ diagrams.
THE CLASSIFICATION OF STARS: UNDERSTANDING THE H-R
DIAGRAM
59. When the absolute magnitude is plotted against the spectral classification
for a large
sampling of stars, the result is known as a
____________________ diagram.
60. The vertical axis of the diagram represents the brightness or
____________________ of
the stars standardized for a distance of 10
parsecs from the sun.
61. The horizontal axis of the diagram represents the spectral classification
of the star which is
really another way of describing the _______________
of the stars being plotted.
62. On this diagram, most stars are located along a curved track which
is called the
____________________. Stars throughout this
location have much the same internal
structure and composition and are existing through
much the same processes. They are fusing _______________
into _______________ to create the energy which powers their
existence. Stars spend most of their ________________
at this location. Do not think of the
curve as a sliding board, where stars start
at the upper left and work their way down to the
lower right by the time of their demise.
63. The feature about the stars which leads to the correlation of
the pattern which we term the
main sequence on an H-R diagram is a direct
result of that star? _______________.
64. Along the main sequence, low luminosity stars are COOL/HOT (circle
one) stars, while
high luminosity objects on the main sequence
are COOL/HOT (circle one).
65. Stars which lie at the lower right of the main sequence are low
luminosity and therefore have HIGH/LOW (circle
one) masses. Stars which lie at the upper left of the main sequence
are of high luminosity. These object have HIGH/LOW
(circle one) masses.
66. A star is a balancing act between the mass of the object which
wants to _______________ the star due to gravitational
forces, and the outward _______________ created by the
thermonuclear fusion processes which are generated
by a star? internal temperatures pushing
against this force of gravity. Low mass/low
luminosity stars have less internal compression
and have lower temperatures. Their lives must
be extremely _______________ for they
consume themselves very slowly. High mass/high
luminosity stars have tremendous internal
compressions and extremely high temperatures.
They consume hydrogen at a prodigious rate. Their
longevity on the main sequence must be extremely _______________.
67. Since stars which fall along the main sequence are believed to
have the same internal
_______________, it can be inferred that stars
which lie off the main sequence must have
internal structures which are quite different.
One of these classifications is represented by
stars which are very luminous. Their spectra
indicate that they are very cool. Since cooler
stars emit MORE/LESS (circle one) energy per
unit area, the only way that they can be very
luminous is if they are very _______________.
These types of stars are called
____________________.
68. On the other hand there are stars which according to their spectra
are extremely hot,
emitting a lot of energy per unit area. However,
these objects are not very luminous. In size,
these stars must be very _______________. Stars
which fall into this category are labeled
____________________.
69. Supergiants, giants, main sequence, and white dwarf stars represent
four different types of
_______________ classifications found on the
H-R diagram. These regions represent
different ________________ stages which a star
may pass through during its lifetime.
70. Stars which are not found along the main sequence are utilizing
different processes other
than core hydrogen burning to sustain their
existence. Giants are converting hydrogen into
helium in a thin _______________ surrounding
their cores. Eventually temperatures may
become hot enough to initiate helium burning
in the star's interior. Some supergiants have
gone through core helium burning, and they are
now converting _______________ into
carbon and oxygen in a thin shell surrounding
their carbon-oxygen rich cores.
71. White dwarfs are really the hot, inert helium or carbon-oxygen
_______________ from
dead, low mass stars which have shed their outer
envelopes of hydrogen and helium. The
mass of the "star" is sustained from
further collapse due to the pressure of
_______________. Matter in this particular condition
is said to be _______________.
72. On the H-R diagram the sun is placed in the middle of the main
sequence because it is
considered to be an _______________ star. Stars
which are at the upper left of the main
sequence are very ________________ and ________________.
Their core temperatures
and pressures must be much higher than the sun's.
Their sizes in comparison to the sun's size
must also be LARGER/SMALLER (circle one). The
only way that these conditions can be
generated is if these stars possess greater
internal compression created by more
_______________. Because a star's luminosity
varies approximately to the 3.5 power of its
mass, these stars have LONG/SHORT (circle one)
lives.
73. Stars at the lower right hand corner of the main sequence of the
H-R diagram are cool and
not very luminous. Their internal _______________
and _______________ are less
because their masses are less. Glowing with
a cool, red color, these stars consume their
nuclear fuel so slowly that their lives will
be very _______________ indeed.
74. With respect to solar masses, the numbers ________ to ________
represent the lower and upper limits of all
stars found in the sky. This translates into a luminosity of less than
1/7000th
to more than 1,000,000 times that of the sun's
brightness.
75. In addition to allowing stars to be classified with respect to
luminosity, mass, and size, an H-
R diagram allows astronomers to trace the e_______________
tracks of these objects as
well.
STELLAR BIRTH
76. Stars are born when large masses of gas and dust gravitationally
_______________. The
greater the mass, the FASTER/SLOWER (circle
one) this process takes place. The range in
time can be from tens of thousands to nearly
100 million years.
77. When contraction begins, these protostars are cool, but very _______________.
This
indicates that they are very (size) _______________.
On the H-R diagram low mass stars
move _______________ (direction) and then to
the _______________ (direction) as they
are formed.
*78. As contraction proceeds in the early stages of the formation
of a low mass star, the surface brightness remains
constant while the size _______________. These stars become less
luminous. Energy is released as gravity pulls
the material which will form the star closer
together and temperatures and pressures increase.
Energy is transported to the surface via
_______________ currents (turbulence). During
contraction low mass stars are immersed in a
cocoon of _______________.
*79. Once the low mass star niches to the left, a different mode of
energy transportation, called
_______________ transfer becomes dominant in
its interior. The cocoon of dust is shed,
revealing the true protostar as an optical object.
Internal temperatures and pressures
approach the level where full _______________
burning can be sustained. Luminosity
remains fairly constant.
*80. In the formative processes, the most massive stars basically move
to the
_______________ (direction), on the H-R diagram,
maintaining their luminosities at the
expense of a decrease in size. T________
must be going up very rapidly to sustain this
constant energy output despite a smaller surface
area. In the end when hydrogen burning
commences, these stars are substantially larger
than our sun due to the enormous pressures
which are generated in their cores through the
accelerated burning of hydrogen. These stars
are often called ____________________.
81. Once a star initiates hydrogen burning, it lies somewhere along
the _______________ ___
at a position called its ________________ age
location. A star's specific position along this
curve is essentially determined by its ________________.
82. Since a random sampling of stars in the sky will show that most
stars fall along the main
sequence, it can be said that stars spend the
greatest portion of their lives converting
________________ into _________________.
STELLAR DEATH
83. As thermonuclear fusion proceeds _______________, ash builds up
in the star's core. The
core becomes smaller as gravity squeezes this
inert material into ever higher densities.
84. Contraction of the core causes core temperatures to INCREASE/DECREASE
(circle one),
ACCELERATING/DECELERATING (circle one) hydrogen
burning in the core. The star
becomes slightly MORE/LESS (circle one) luminous,
but is still considered to be on the main
sequence.
85. Eventually all hydrogen burning ceases in the core. Hydrogen begins
to fuse in a thin
______________ surrounding the core, adding
more helium ash into the system. Because no
fusion is occurring in the core, it continues
to contract under the force of gravity, eventually
reaching a fraction of its original size. Temperatures
in this region INCREASE/DECREASE
(circle one) dramatically, causing an acceleration
in the star? shell hydrogen burning, lifting the star's
outer layers.
86. Temperatures in the outer layers of the star INCREASE/DECREASE
(circle one), but
because the size of the star has become so much
larger the actual _______________ has
increased. At this point the star rapidly moves
away from the main sequence, to become a
_______________.
87. When the core of the star reaches 100 million K, _______________
nuclei begin to fuse.
In higher mass stars this begins gradually,
but in less massive stars, the onset is explosive, and it
is known as the ____________________. The fusion of helium atoms into
carbon is called the _______________ process.
88. When the helium flash occurs in low mass stars, the core expands
and WARMS/COOLS
(circle one), reducing the amount of fusion
in the hydrogen burning shell. This causes the
bloated outer layers to contract because they
are no longer being supported by as much
pressure from the hydrogen burning shell. The
star backs away from its high point in
luminosity on the H-R diagram and moves to the
left. *Low mass stars in this region of the H-
R diagram are known as h______________
-branch stars.
89. A post helium flash, low mass star is a WARMER/COOLER (circle
one) and
BIGGER/SMALLER (circle one) object than when
it was a red giant.
90. As helium burning occurs in the core of low mass stars, the ash
which results is chemically
known as _______________ and oxygen. Eventually
most of the helium in the star's core is
consumed. The ash compresses and is further
heated, triggering helium burning in a
_______________ surrounding the core. Since
conditions in the core are hotter than ever
before, the star ascends the giant branch once
again, but not merely as a red giant. This time
the star becomes a _______________ red giant
star. Astronomers are not really sure
whether the sun will reach this final stage
in its evolutionary cycle or whether the sun will even
initiate helium fusion within its core.
91. In low mass stars, instabilities can develop in the helium burning
shell which eventually lift the outer layers
of the star from its core. The expanding sphere of luminous gas is called
a
_____________________ nebula. The remaining
hot, compact core is called a
_____________________. Over billions of years
this object will eventually cool to become
a _____________________.
92. The evolution of more massive stars follows a sequence of core
and shell burning which
produces heavier and heavier _______________.
Like a low mass star, hydrogen is
changed into helium and helium into carbon and
oxygen. But because high mass stars have
higher internal pressures and temperatures,
the energy production can continue to more
interesting later stages where carbon and oxygen
are converted into silicon, sulfur, argon,
calcium and finally _______________.
93. By this time the massive star's life is almost over. Its interior
is segregated into
_______________, where successive elements are
burning, each producing less energy than
the last, and each reaction taking a LONGER/SHORTER
(circle one) amount of time over
the previous stage.
94. All fusion reactions up to iron have been _______________, meaning
that energy is given off during the fusion reaction.
To produce heavier atoms beyond iron necessitates the input of energy.
These nuclear reactions are _______________.
95. At the heart of the star an iron core rapidly begins to grow as
the process of nuclear fusion
can go no further. When enough iron has been
produced in the innermost regions of the star,
gravity takes over and the core _______________
almost instantaneously (about 2/10 of a
second), producing temperatures and pressures
found nowhere else in the universe.
96. During the collapse, complex iron nuclei in the core are broken
down into simpler elements,
and electrons are forced into protons to form
neutrons with the subsequent release of
_______________. A shock wave is produced as
the imploding material bounces off the
core and is lifted by the pressure of the neutrinos
passing through the incredible nuclear
densities which have been created by the collapse.
This whole event takes place in
SECONDS/DAYS/YEARS (circle one).
97. The result of this action is a prodigious outburst of energy known
as a _______________.
During the explosion, elements _______________
than iron are synthesized.
98. What is left after the detonation is a core of nuclear material
about 10 miles in diameter
known as a _______________ star, surrounded
by an expanding cloud of gas containing the elements
that can make other planetary systems, stars, or even, if given enough
time, human
beings.
99. The event mentioned in the previous statement is termed a TYPE
I/TYPE II (circle one)
supernova. The spectrum is dominated by _______________
lines, because that gas is still
very abundant in the star's outer layers.
*100. In a TYPE I/TYPE II (circle one) supernova, hydrogen from a
_______________ star
in a binary system accretes onto a white dwarf
composed of carbon and oxygen. Eventually
the increase in mass, with its resulting increase
in pressure, nearly forces the dwarf to become a
neutron star; however, before this can occur, carbon burning is initiated.
*101. Because the material of the white dwarf is in a state of d________
, there is no increase
in pressure as carbon burning ensues. Because
of this there is no expansion of the gases as a
result of the energy being released. The carbon
burning accelerates, eventually producing so
much energy that the material in the star can
no longer remain in a state of degeneracy.
However by this time it is too late. Now obeying
the perfect gas laws, this plasma rapidly
_______________, causing the star to blow apart
or consume itself in a rapid thermonuclear outburst.
102. Amongst the billions of galaxies contained within the universe,
it is hypothesized that
supernovas occur with a frequency approximating
one event each _______________.
However, very few of these stellar deaths are
observed from earth each year because of
intervening dust, distance, and the lack of
adequate search patrols to locate these objects.
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