Week 1 - How the elements are formed Flashcards
• When we use the term _____ we are discussing the
totality of all matter, energy, and space.
Universe
___ and ____ emit the full spectrum of
electromagnetic radiation.
Stars and galaxies
• Unfortunately for the astronomers, the Earth‟s protective
atmosphere also absorbed much of the incoming
radiation from the non-visible wavelengths.
• Scientists were soon devising ways to minimize or
eliminate the Earth‟s atmospheric filtering.
• Observatories were located on high mountains where the
atmosphere is thin .
• Balloons, aircraft, satellites, and spacecraft were utilized
to transport instruments to ever greater heights.
Studying the universe
• While the galaxies are all moving away from each other at
the present time, they must have been closer together in
the past.
• The universe must have been much more compressed.
• In fact most astronomers think that the universe began as
a small, hot, extremely dense entity that rapidly expanded
(exploded) about 14 billion years ago – ______
The big bang
• With our present knowledge of subatomic particles and
the structure of the universe we can extrapolate back to
about _____ second of the Big Bang.
10-43 sec
• Experimental evidence supports the Big Bang in three
major areas:
• ________– galaxies today have a redshift in
their spectrum lines
• ________– microwave radiation
that fills all space and is thought to represent the
redshifted glow from Big Bang
• There is a H to He mass ratio of 3 to 1 in the stars and
interstellar material, as predicted by the Big Bang model.
Cosmological redshift – galaxies today have a redshift in
their spectrum lines
• Cosmic microwave background – microwave radiation
that fills all space and is thought to represent the
redshifted glow from Big Bang
• There is a H to He mass ratio of 3 to 1 in the stars and
interstellar material, as predicted by the Big Bang model.
• With a doubt, our current knowledge of the formation of
the universe is incomplete.
• In 1980 the standard model was modified.
• This proposes that the universe
consists of a large number of separate regions – formed
at about 10-35 second.
• We can only detect information from one of these regions
– our “universe.”
Big Bang - Standard
& Inflationary Models
• Much greater expansion took place between 10-35 second
and 10-30 second than in the standard model.
Inflationary Model of the Big
Bang
• If the _______ is correct the entire universe is
gigantic and the portion that we can observe is only a tiny
fraction of the whole.
• At the present time the _______ is the best
theory to explain the origin of the universe.
Inflationary Model
• this is a self-luminous sphere of hot gases, energized
by nuclear reaction and held together by the force of
gravity.
• the nearest star to Earth.
• enormous in size relative to the size of Earth.
• _______ diameter is approximately 100 times the diameter of
the Earth.
The Sun: Our Closest Star
The Sun can divided into four concentric layers:
• The innermost core
• The “surface” is called the photosphere.
• The chromosphere is a layer of very hot gases above the
photosphere.
• The corona is the Sun‟s outer solar atmosphere.
The this is the bright and visible “surface” of the
Sun.
• Temperature of 6000K
• Composition of 75% H, 25% He, and 1% C, O, N, Ne, and
others
• When viewed close-up, the photosphere surface appears
to have a „granular‟ texture.
• Each granule is a hot spot caused by an individual
convection cell bringing thermal energy to the surface.
• Each granule is about the width of Texas.
Photosphere
• are huge patches of cooler, and therefore
darker material on the surface of the Sun.
• They are a distinctive feature of the photosphere.
Sunspots
• The abundance of sunspots vary through an ____
sunspot cycle.
• Each sunspot cycle begins with the appearance of a few
sunspots near the 30o
“N & S” latitudes.
• The number of sunspots slowly increase, with a maximum
number in the middle of the cycle at around the 15o
region.
• The number of sunspots then slowly taper off during the
last half of the 11-year cycle.
Sunspot Cycle
11 year
Interestingly, this also have magnetic polarity.
• Each 11-year cycle is similar except that the polarities are
reversed.
• Therefore the 11-year sunspot cycle is actually a
manifestation of a more fundamental 22-year magnetic
cycle.
Sunspot Cycle
• ________‟s temperature is approximately 1 million K.
• Prominences occur within the corona region of the Sun.
Corona
• In the extreme high-temperatures of the corona protons,
electrons, and ions are furnished with enough energy to
escape the Sun‟s atmosphere.
• These particles are accelerated enough to escape the Sun‟s
tremendous gravitational pull.
• The solar wind extends out from the Sun at least 50 AU.
Solarwind
• The Sun‟s ______ is so hot that individual atoms cannot
exist.
• Continuous high-speed collisions result in the separation of
nuclei and electrons.
Interior of the Sun
• Moving outward from the core of the Sun, both the
temperature and the density decrease.
• It is the nuclear fusion of ______ within the core that is
the source of the Sun‟s energy.
• In the Sun and other similar stars the nuclear fusion takes
place as a three step process called the
Interior of the Sun
H into He
Proton proton chain
In the net reaction of the PP Chain, four protons form a
He nucleus, two positrons, two neutrinos, and two gamma
rays.
• The amount of energy released by the conversion of
mass conforms with Einstein‟s equation, E = mc2
Proton-Proton Chain
• Approximately 6.00 X 1011 kg of H is converted into 5.96
X 1011 kg of He every second
• With a total mass of 1030 kg of H, scientists expect the
Sun to continue to radiate energy from H fusion for
another
5 billion years
The Earth only receives a very small percent of the Sun‟s
radiated energy.
• Every second the Earth receives approximately 1.4 x 103
W/m2
, a value known as ______
• Even a very small variation (+/- 0.5%) in the solar
constant would have disastrous effects on our planet‟s
biota.
Solar Constant
Recall that stars are composed dominantly of ____, with
some ____, and far lesser amounts of other elements.
• They exist as huge plasma spheres in which nuclear
fusion of H to He produces enormous amounts of energy
that is emitted.
• Although star masses can vary considerably, most have a
mass between 0.08 – 100 solar masses.
• One solar mass = mass of our Sun
H and He
• Most stars are part of a ______ system, unlike our
Sun that is a single star.
Multiple star system
• This Diagram results from plotting the stars‟ absolute
magnitudes versus the temperatures of their
photospheres.
The H-R
(Hertzsprung-Russell) Diagram
• Several types of star do not fall on the main sequence.
• these are very large stars that are cool, yet still very
bright
• The very brightest are called • these are stars that are very hot, yet are dim due to
their small size
Stars off the H-R Main Sequence
• Several types of star do not fall on the main sequence.
• Red giants – very large stars that are cool, yet still very
bright
• The very brightest are called red supergiants.
• White dwarfs – stars that are very hot, yet are dim due to
their small size
__________ of stars shows that even the most
distant stars contain the same elements we find in our
solar system.
• However, there are variations in the spectra depending
on the temperature of the individual star‟s photosphere.
• Therefore, the patterns of the absorption lines in the
spectra can be used to determine both the composition
and the surface temperature.
Spectral Analysis of the Stars
• In the _____, stars have been placed in seven
spectral classes – O,B,A,F,G,K,M.
• Note the horizontal top axis of the diagram.
H-R Diagram
• Our ____ falls close to the middle of the main sequence
and is a class G star.
• this is the closest star to Earth (besides our Sun)
and is a red dwarf or class M star.
• Our Sun falls close to the middle of the main sequence
and is a class G star.
• Sirius is quite a bit hotter than our Sun and is a class A
star.
• Astronomers have found that the majority of stars are
small, cool, class M stars, also called red dwarfs.
• Proxima Centauri is the closest star to Earth (besides our Sun)
and is a red dwarf or class M star.
• – gases and dust that is distributed
amongst the stars
• The gases consists of about 75% H, 25% He, and a trace
of heavier elements by mass.
• The dust (only about 1% of the interstellar medium)
consists primarily of C, Fe, O, & Si.
• About the size of particles in smoke
Interstellar Medium
• The gases and dust do not appear to be distributed
uniformly throughout space.
•________ – concentrations of cool, dense clouds of gases
and dust
• Two major types of ____exist: bright and dark
Nebulae
• Bright nebulae can, in turn, be divided into:
• Emission nebulae – energy from nearby stars ionize the
hydrogen gas resulting in fluorescence
• Reflection nebulae – dust within the nebulae reflect and scatter
starlight, giving off a characteristic blue color
• The most famous of the _____66 is located in the
constellation Orion.
• It appears like the head of a horse, back-lit by a bright
emission nebula.
Dark nebulae
• Stars begin to form as interstellar material (mostly H)
gathers together. (accretion)
• The accretion of the interstellar material may be due to
several factors:
• Gravitational attraction of the material
• Radiation pressure from nearby stars
• Shockwaves from exploding stars
• A protostar forms as the interstellar material condenses
and the temperature rises.
General Evolution of a Low-Mass
Star
• As the _____ continues to condense, the temperature
continue to rise.
• As the temperature continue to rise, the thermonuclear
reaction begins in which H is converted to He. (fusion)
• Recall the reaction below:
Protostar
• When ______ begins, this is the time a star
is actually born.
• It moves onto the H-R main sequence, in a position
determined by its temperature and brightness.
• Ultimately both temperature and brightness are dependent upon
the star‟s mass.
Star is born
thermonuclear fusion
• As the star continues to fuse H into He, it remains on the
H-R main sequence.
• The period of time that a star remains on the main
sequence can vary widely.
• A ____ star, such as our Sun, will remain on the main
sequence for 10 billion years.
• A _____ star may stay on the main sequence for
trillions of years.
Low mass star
• As H in the core continues to convert to He, the core
begins to contract and heat up even more.
• This extra heat eventually causes the H in the
surrounding shell to proceed more rapidly, which in turn
destabilizes the star‟s hydrostatic equilibrium, resulting in expansion.
• At this point, when the star expands, it enters the redgiant phase, and moves off the main sequence.
Stellar evolution
When our Sun moves into its ______ phase (several
billion years from now) it will swell and engulf Mercury
and possibly Venus.
• The core of a red-giant eventually becomes so hot that
He will fuse into C and perhaps will create elements up
through Ne.
• this is the creation of elemental nuclei inside
stars.
• In high-mass red supergiants nucleosynthesis may
continue all the way up to Fe.
Red giant phase
This occur in the star‟s temperature and brightness
during the red-giant phase.
• For a short time it becomes a variable star, as its position
on the H-R diagram moves left.
Variation
• During and after the ______ stage the star becomes
very unstable, resulting in the outer layers being blown off
forming a planetary nebula.
• Planetary nebula have nothing to do with planets.
• Early and fuzzy photographs of planetary nebula reminded
astronomers of an evolving solar system.
• The expelled material diffuses into space, providing
material for future generations of stars.
Variable star
• Following the formation of a planetary nebula the
remaining core is called a ____
• Thermonuclear fusion no longer occurs in a ____
and it slowly cools by radiating its residual energy into
space.
•______are not very bright and fall low on the H-R
diagram.
• A single teaspoon a matter in a ____ may weigh 5 tons!
White dwarf
This is a class-A
main sequence star.
• _____ is a white dwarf
at about 5 o‟clock.
Sirius A and B
• During stellar evolution, what if a protostar cannot sustain
thermonuclear fusion due to its small mass?
• In this situation the protostar would not progress to the
star phase and would result in a
• Obviously _____ are very dim.
• The first ____ was not discovered until 1996. –
Gleise 229B
• About 100 _____ have now be found.
Brown Dwarfs
• _____ stars and low-mass stars form initially in
similar manners.
• _____ stars are hotter and brighter than low-mass
stars.
• _____ star move onto the main sequence at higher points.
• ______ stars do not stay on the main sequence as
long as low-mass stars, due to their higher rate of
thermonuclear fusion.
High-Mass Star
When high-mass stars moves off the main sequence they
become red supergiants and eventually explode as _____. Much of the material is scattered into space
leaving behind a neutron star or black hole.
Type II Supernovae
As we have learned in sections 18.4 & 18.5, the initial
mass that a celestial object acquires during its formation
is very important in determining its eventual fate.
• But the final mass left over after any stellar material is
ejected turns out to be the conclusive determinant
Mass and Stellar Evolution
Thses are giant assemblages of stars.
Galaxies
These deals with the structure and evolution of the
universe.
Cosmology
•
• For many years we were only able to gather information
from one type of emitted electromagnetic radiation –_______
Visible light
• In 1931 _____ became operational, giving
scientists the ability to start gathering information from
other wavelengths
Radio telescopes
• Initially the universe was filled with ___
•
Protons
• Within the first 4 seconds ___,___ and ___ formed.
protons, neutrons, and
electrons
D and He nuclei formed in the first ____ minutes.
3 mins
After about ½ million years gravity began forming
____ and ____
Galaxies and stars
A fourth phase of matter, called a ______ is created
where nuclei and electrons exist as a high-temperature
gas.
Plasma
• The temperature at the central core of the Sun is
15 million K and the density is 150 g/cm3
The innermost 25% of the Sun, the ____, is where H is
consumed to form He
Core
This is the volume or “bubble” of space formed by
the solar wind.
Heiliosphere
Virtually all the material in the heliosphere emanates from the
Sun
are bright explosive events that occur on the Sun‟s
surface.
Flares
are enormous filaments of solar gases that
arch out and over the Sun‟s surface.
• may extend hundreds of thousands of km
outward.
Prominences
• The late 1600‟s were an unusually cold period on Earth,
marked by an anomalously fewer number of sunspots.
• In Europe this time was known as the ______
• Apparently, there is a strong connection between solar
activity, as displayed by sunspots, and global climates on
Earth
Little ice age
The this is the pearly white halo or crown extending
far beyond the solar disk
• Visible during total eclipses of the Sun.
• This can be interpreted to be the Sun‟s “outer
atmosphere.”
Corona
stars that consist of two close stars each
orbiting about their shared center of mass
Binary star
• Most stars are part of a _____ system.
Binary system
• There are also _____ systems with three or more closely
spaced stars but these are far less frequent.
Star system
• Most stars become brighter as they
Hotter
• These stars plot as a narrow diagonal band in the
diagram.
H-R DIAGRAM
• The hottest (and generally brightest) stars are _____. The
coolest (and generally least bright) stars are _____
• The hottest (and generally brightest) stars are blue. The
coolest (and generally least bright) stars are red.
This is quite a bit hotter than our Sun and is a class A
star.
Sirius
Astronomers have found that the majority of star are
small, cool, class M stars, also called
Red dwarfs
energy from nearby stars ionize the
hydrogen gas resulting in fluorescence
Emission nebulae
dust within the nebulae reflect and scatter
starlight, giving off a characteristic blue color
Reflection nebulae
• – produced by the obstruction of a relatively
dense cloud of interstellar dust
• are visible as relatively dark areas as they
are framed against some type of light-emitting region
behind them.
Dark nebulae
_____ stars fuse fuel fast, and only remain on the
main sequence a few million years.
High mass star
