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Lecture 4: The Life-Cycles of
Stars
Astronomy 5: The Formation and Evolution of the Universe
Sandra M. Faber
Spring Quarter 2007
UC Santa Cruz
The visible-light spectrum of the Sun is wrapped here end to end from
red to blue. The dark “lines” are wavelengths that are absorbed by
atoms in the Sun’s outer layers.
There are millions
of “lines” in the
Sun’s spectrum.
H
The strengths of
the lines are
related to the
number of atoms
of each element.
Na
Mg
Modeling these
features allows us
to measure the
Sun’s
composition.
H
Na
Mg
The simplest nuclear reaction that makes stars
shine
The HR (Hertzsprung-Russell) Diagram (1913)
The strip is called the
Main Sequence.
For a star, mass is
destiny.
Mass determines
where you lie on the
main sequence, how
bright you shine, and
how long you live.
Radii
100
10
1 sol rad
0.1
0.01
Radii
100
10
1 sol rad
0.1
0.01
The HR (Hertzsprung-Russell) Diagram (1913)
Notice that a 100 solar
mass star is about a
million times brighter
than the Sun.
It has 100 times more
fuel but uses it up a
million times faster.
It therefore lives only
about 10-4 times as long
as the Sun.
Since the Sun lives 10
billion years, a 100
solar mass star lives
only about one million
years.
Massive stars
have shorter
lives.
A star cluster of 10,000 stars all formed at the same
QuickTime™
and
a
time. The
HR
diagram
evolving
with time.
YUV420 codec decompressor
are needed to see this picture.
One of the most famous diagrams in astronomy: a
collection of HR diagrams for star clusters of different
ages.
Stellar populations in the Andromeda galaxy
Red bulge,
“red and
dead”
Blue disk,
star forming
Star forming regions
in M33, a small
spiral neighbor of
the Andromeda
galaxy
Stars form from dense clouds of
gas
Messier 33 galaxy, a nearby
member of the Local Group
The Orion Nebula: a typical H II region*
* H II means hydrogen is
ionized, H I means neutral.
H II glows in visible light, H I
emits only radio waves.
In the heart of the Orion Nebula…
In the heart of the Orion Nebula…
Flying through the center of the Orion Nebula
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
17 times Pluto’s orbit
Orion “proplyd”
A rotating proto-solar nebula: “rocks” seem to be
the seeds of planets
QuickTime™ and a
MPEG-4 Video decompressor
are needed to see this picture.
Supernovae seed the interstellar gas with heavy
elements, which are the “ashes” of nuclear burning.
They come from massive stars, above 8 solar
masses.
C
N
O
Si
Fe
The Crab nebula
supernova
remnant
etc...
Order these star clusters by age
A major recent discovery: color bimodality
A major recent discovery: color bimodality
A major recent discovery: color bimodality