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The Stages of Stellar
Evolution
1
Starbirth - What is needed
• Large molecular cloud
ranging from 1 light
year to 300 light years
across
• A density of about
10^7 molecules per
square inch
• A temperature range of
–440 degrees F to 1000
degrees F
• Each cloud could
make up to 100,000
stars the size of our
Sun
Kinda looks like a
Middle finger.
2
Formation of Molecular
Clouds
•
The interstellar medium of the
Galaxy is the space between the
stars. It is not void, but filled with
vast amounts of gas and dust. The
ISM of a Galaxy has a mass of
several billion times that of it’s stars.
•
Unlike the vast majority of this
space, which are wide open
frontiers containing but few atoms,
some areas have densities about
1,000 times greater. In these spaces
many atoms combine into
molecules, and molecular clouds
form from gas clouds.
•
Molecular clouds tend to form the
colder part of the ISM, with
temperatures as low as 10K.
Molecular Cloud Barnard 68
Credit: FORS Team, 8.2-meter VLT Antu, ESO
3
Facts on
Molecular clouds:
Molecular clouds in our galaxy have diameters
ranging from less than 1 to 300 light-years. These
contain enough gas to form from about 10 to 10
million stars like our Sun.
Molecular clouds that exceed the mass of 100,000
suns are called Giant Molecular Clouds.
A typical full-grown spiral galaxy contains about
1,000 to 2,000 Giant Molecular Clouds and many
more smaller ones.
Molecular clouds were first discovered in our
Milky Way Galaxy with radio telescopes about 25
years ago.
Most of the gas within molecular clouds is about
-440 degrees Fahrenheit.
Since gas is more compact in a colder climate, it is
easier for gravity to collapse it to form new stars.
Sources include:
http://antwrp.gsfc.nasa.gov/apod/ap990511.html
http://oposite.stsci.edu/pubinfo/pr/1997/34/af2.html
Due to these low temperatures, the same climate
that is conducive to star formation also may shut
off the star birth process.
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Starbirth in Nebulae
• Causes of
Starbirth in
Nebulae.
•
Nebulae are set in motion by a
supernova shock wave, rocky
body, change in magnetic fields,
etc.
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Pretty
6
THE PROTOSTAR
A dense ball of gas
and dust forms a
protostar. Over time,
accumulation of
matter and
compression of the
core by gravity
causes it to heat up.
Heat radiates into the
surrounding cloud,
causing it to become
bright.
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Brown Dwarf Stars
 Brown dwarfs are
believed to exist
throughout the
galaxy.
 They are too low
mass to produce
helium so they give
off little light and
are difficult to
locate.
 Basically they are
giant Jupiter’s.
http://www.spaceflightnow.com/news/n0008/24hstbrown/
8
Protoplanet Formation
• The process of solar
evolution was first
described by Pierre
Simon de Laplace. He
believed that a nebula
will contract under its
own gravity creating a
central star (nebular
theory). The remaining
material orbits the star
and in time is flattened
into a disk. The
material in this disk
forms protoplanets.
9
Protoplanets Clean up
Like condensation of a rain drop around a
dust particle protoplanets sweep up the
interstellar dust clouds as seen in this
picture.
• Just as the central star in our
system formed, the
protoplanets too form from
their own gravity. As the disk
material orbits a star the tiny
particles attract each other and
form slightly larger object. As
these planets-to-be grow, their
ability to attract the
surrounding gases increases
so that in time the protoplanets
will actually suck the newly
formed solar system clean.
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Existing Protoplanets
•
•
An existing
protoplanet is
shown here.
Located in the
constellation of
taurus
For more
information visit
<http:www.Windows
.Ucar.Edu>
FAST FACTS:
Star Name:
Planet name:
Constellation:
Coordinates:
Distance:
Field of view:
TMR-1 (Taurus Molecular Ring, star 1 - binary)
TMR-1C
Taurus
4h39m15s RA, +25d53m Dec.
450 light-years
19 arseconds
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Pre-Main Sequence Stars
• Pre-main sequence stars start
when a protostar has formed
and continues until the star
reaches the main-sequence.
• These stars radiate away
head-energy, but also increase
stellar temperature due to
contraction.
• Pre-main sequence stars also
have negative head capacity.
• Infared color arising from
thermal dust emission are
easily seen in sequence such
as T-Tauri stars
12
A Bow Shock around a Young
Star
Young stars are very energetic,
and may emit intense stellar
winds or gusty flares.
In this picture, one young star
is probably being blasted by
one of its siblings.
13
Specific Classes:
OBAFGKM
• A star’s size predestines (to a degree) its personality and lifespan.
Stable adult Main Sequence stars are related by mass, heat, color,
lifespan,burn-rate, size:
 Spectral class O, B stars (rare, but very interesting): Giant, hot,
bright, blue stars burn up quickly and die violently. Lifetime is only
1-10 million years.
 Spectral class A,F,G,K stars (like the Sun): Middle of the road
habits. Orange, yellow or white in color. Typically will live for 1-20
billion years.
 Spectral class M,R,N, L stars: (most abundant): Small, cool, Red,
and dim. Will burn the slowest and live the longest (about
50billion years).
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Specific Classes:
OBAFGKM
•
What makes up the
stars greatly effects
whether they are
categorized as O, B,
A, F, G, K, M, or L.
This chart shows the
general chemical
make up of stars
related to where they
are placed on the
spectral graph.
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Examples of OBAFGKM
Hottest Stars:
T>30,000 K; Strong
He+ lines; no H
lines (or only very
weak at O9).
The ‘O’ class star.
T=15,000 - 30,000
K; Strong neutral
He lines; very weak
H lines, getting
stronger from B0
through B9.
The ‘B’ class star.
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Examples of OBAFGKM
T=10,000 - 7500
K; Strongest H
lines, Weak Ca+
lines emerge
towards A9
types.
The ‘A’ class star.
T=7500-6000 K; H
grows weaker
through F9, Ca+
grows stronger,
weak metals begin
to emerge.
The ‘F’ class star.
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Examples of OBAFGKM
T=6000-5000 K;
Strong Ca+, Fe+
and other metals
dominate, H grows
weaker through
the class.
The ‘G’ class star.
T=5000-3500 K;
Strong metal
lines, weak CH
& CN molecular
bands begin to
appear, growing
through the
class. H lines
nearly gone.
The ‘K’ class star.
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Examples of OBAFGKM
Cool Stars: T ~2000 3500 K; strong
molecular absorption
bands particularly of
TiO and VO emerge and
strengthen, as do lines
of neutral metals.
Virtually no H lines
anymore.
The ‘M’ class star.
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• These stars are the
smallest, coolest, and
faintest of all.
•Because of this, they are
difficult to view from
Earth.
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Red Giants
As a star runs out of hydrogen to
fuse, its core collapses and sends
a shock wave from the heat
outward, expanding the outer
layers of the star. The
temperature and pressure
conditions in the core increase
enough to induce the fusion of
heavier elements late in its life.
Betelgeuse, pictured at left, is a
red supergiant. It is nearing the
end of its life and will soon
become a supernova.
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Pulsating variable stars vary in brightness because they pulsate in and out.
In the outer layers of pulsating stars, the inward pull of gravity and the
outward push of pressure are out of balance.
When outward pressure overwhelms
inward gravity, the star expands.
However, when inward gravity surpasses outward
pressure, the star contracts.
22
Pulsating variable stars
pulse in size as well as
temperature.
small and hot
big and cool
The pulsations can be regular or irregular, ranging from more than a
year to only a few hours between pulsations. The change in size by about
15% of their radius.
For more info in Pulsating Variable Stars, you can visit:
http://faculty.rmwc.edu/tmichalik/pulsvar.htm
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Planetary Nebulae
Planetary nebulae are formed
when a red giant star ejects its
outer layers as clouds of
luminescent gas, revealing the
dense, hot, and tiny white dwarf
star at its core. Information can
be found at:
http://www.seds.org/billa/twn/
This is one of the most complex of the
planetary nebulae. The HST images seem to
indicate that the central star is actually a
binary system and that the nebula we see
today is actually the result of at least two 24
separate events.
White Dwarf
• White dwarf: A star that
is the remnant core of a
low mass star that has
completed fusion in its
core. The sun will
become a white dwarf.
White dwarfs are
typically composed of
carbon, have about the
radius of the earth, and
do not significantly
evolve further.
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• A white dwarf is a whitish
dead star having low
luminosity, small size
and very great density.
These white dwarf
stars are intensely hot
... but they are
cooling. Their interior
nuclear fires no longer
burn, so they
will continue to cool
until they fade away. 26
The white dwarfs are circled.
Supergiant
• A supergiant is any star of very great
intrinsic luminosity and relatively
enormous size.
• Several magnitudes brighter than a giant
star and several times greater in diameter.
• Their lifetimes are probably only a few
million years long.
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HD 65750
• This supergiant is located in
the center of nebula to the left.
The nebulosity around the star
is the result of light reflected by
dust surrounding it. The dust
consists mainly of silica
condensed from material
which the star is losing from its
surface at a fairly steady rate.
• WWW.phy.mtn.edu/apod/astro
pix.html
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