Download Linking Asteroids and Meteorites through Reflectance

Astronomy 100
Tuesday, Thursday 2:30 - 3:45 pm
Tom Burbine
[email protected]
www.xanga.com/astronomy100
Schedule
• Today – Class
• Tuesday-Class
• Wednesday- Review Session
– Hasbrouck 134 from 7-8 pm
• Thursday-Exam #3 (Chapters 15, 16, 17, 18)
Homework Assignment
(Due Today)
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Make up a test question
Multiple Choice
A-E possible answers
1 point for handing it in
1 point for me using it on test
The question needs to be on material that will be
on the 3rd exam
• 15 people got extra HW credit for me using their
question (or inspiring a question)
OWL assignment (Due Today)
• There is be an OWL assignment due on Thursday
March 31 at 11:59 pm.
• There are 15 questions and a perfect score will
give you 2 homework points.
OWL assignment (Due Tuesday)
• There is be an OWL assignment due on Tuesday
April 5 at 11:59 pm.
• There are 15 questions and a perfect score will
give you 2 homework points.
Things to remember
• 90% of classified stars are on main sequence
• Main sequence stars are “young” stars
• If a star is leaving the main sequence, it is at the
end of its lifespan of burning hydrogen into
helium
Remember
• Largest stars on main sequence are O stars
• Largest stars that can exist are supergiants
You need to know stellar classifications
• O, B, A, F, G, K, M
• A0, A1, A2, … A9 in the order from the hottest to
the coolest
wd
white dwarfs
Classifications
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Sun is a G2 V
Betelgeuse is a M2 I
Vega is a A0 V
Sirius is a A1 V
Arcturus is a K3 III
Binaries
• About half of stars orbit a companion
• 3 classes of binaries
Visual Binary
• We can see the stars rotating around each other
with a telescope
Eclipsing Binary
The light from a star system drops as a star goes in front
and behind another star.
Spectroscopic Binary
The spectral lines of a star can be seen to be moving to
shorter wavelengths and also to longer wavelengths
Importance of Binaries
• It allows you to possibly determine a star’s mass
if you know the orbital period and the separation
of the two stars
Life of a Star
• A star-forming cloud is called a molecular cloud
because low temperatures allow Hydrogen to
form Hydrogen molecules (H2)
• Temperatures like 10-30 K
• Denser than surrounding regions
Region is approximately 50 light years across
Condensing
• Molecular clouds tends to be lumpy
• These lumps tend to condense into stars
• That is why stars tend to be found in clusters
Protostar
• The dense cloud fragment gets hotter as it
contracts
• The cloud becomes denser and radiation cannot
escape
• The thermal pressure and gas temperature start to
rise and rise
• The dense cloud fragment becomes a protostar
When does a protostar become a star
• When the core temperatures reaches 10 million K,
hydrogen fusion can start occurring
3 Basic Groups of Stars
• Low-mass stars – born with less than 2 Solar Masses
• Intermediate-mass stars – born between 2 and 8 solar
masses
• High-mass stars – born with masses greater than 8
solar masses
Things you need to know
• Fusion rate increases with increasing temperature
• There is a relation between thermal pressure and
gravity
Animation
• Death sequence of the Sun
Sun ends it time on the main sequence
• When the core hydrogen is depleted, nuclear
fusion stops
• The core pressure can no longer resist the crush of
gravity
• Core shrinks
Why does the star expand?
• The core is made of helium
• The surrounding layers are made of hydrogen
And ..
• Gravity shrinks the inert helium core and
surrounding shell of hydrogen
• The shell of hydrogen becomes hot for fusion
• This is called hydrogen-shell burning
And …
• The shell becomes so hot that its fusion rate is
higher than the original core
• This energy can not be transported fast enough to
surface
• Thermal pressure builds up and the star expands
And ..
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More helium is being created
Mass of core increases
Increases its gravitational pull
Increasing the density and pressure of this region
When
• When helium core reaches 100 million Kelvin,
• Helium can fuse into a Carbon nucleus
Helium Flash
• The rising temperature in the core causes the
helium fusion rate to rocket upward
• Creates a lot of new energy
However
• The core expands
• Which pushes the hydrogen-burning shell
outwards
• Lowering the hydrogen-burning shell’s
temperature
And
• Less energy is produced
• Star starts to contract
Now
• In the core, Helium becomes Carbon
• Star contracts
• Helium fusion occurs in a shell surrounding the
carbon core
• Hydrogen shell can fuse above the Helium shell
• Inner regions become hotter
• Star expands
Can Carbon undergo fusion?
• Yes, but can’t reach the needed temperature
(600 million Kelvin) in a low-mass star
• Carbon on Earth is produced in the cores of stars
Planetary Nebulae
• There is a carbon core and outer layers are ejected
into space
• The core is still hot and that ionizes the expanding
gas
Planetary Nebulae
White Dwarf
• The remaining core becomes a white dwarf
PRS Question
• At the end of the Sun’s lifespan when it becomes
a white dwarf, the white dwarf will be mostly
composed of
• A) Hydrogen
• B) Helium
• C) Carbon
• D) Oxygen
• E) Iron
PRS Question
• At the end of the Sun’s lifespan and it becomes a
white dwarf, the white dwarf will be mostly
composed of
• A) Hydrogen
• B) Helium
• C) Carbon
• D) Oxygen
• E) Iron
High-Mass Stars
• The importance of high-mass stars is that they
make elements heavier than carbon
• You need really hot temperatures which only
occur with the weight of a very high-mass star
Stages of High-Mass Star’s Life
• Similar to low-mass star’s
• Except a high-mass star can continue to fuse
elements
• When the fusion ceases, the star becomes a
supernova
• Supernova is a huge explosion
Fusion in High-Mass stars
• Besides fusion of Hydrogen into Helium
• The high temperatures allow Carbon, Nitrogen,
and Oxygen to be catalysts for converting
Hydrogen into Helium
CNO cycle
Fusion
• The temperatures of high-mass stars in its latestage of life can reach temperatures above 600
million Kelvin
• Can fuse Carbon and heavier elements
• Helium Capture can also occur where Helium can
be fused into heavy elements
Supernovas
• We will discuss next class
PRS for making it through class
Questions