Lecture 4: The Life-Cycles of Stars

1
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

2
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 Suns outer layers.
There are millions of lines in the Suns
spectrum.
The strengths of the lines are related to the
number of atoms of each element.
Modeling these features allows us to measure the
Suns composition.
3
The simplest nuclear reaction that makes stars
shine
4
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.
5
(No Transcript)
6
(No Transcript)
7
Radii
100
10
1 sol rad
0.1
0.01
8
Radii
100
10
1 sol rad
0.1
0.01
9
A real HR diagram
The 22,000 nearest stars (distances measured by
the Hipparcos satellite)
Sun
10
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.
11
A star cluster of 10,000 stars all formed at the
same time. The HR diagram evolving with time.
12
One of the most famous diagrams in astronomy a
collection of HR diagrams for star clusters of
different ages.
13
Stellar populations in the Andromeda galaxy
Red bulge, red and dead
Blue disk, star forming
14
Star forming regions in M33, a small spiral
neighbor of the Andromeda galaxy
15
Stars form from dense clouds of gas
Messier 33 galaxy, a nearby member of the Local
Group
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
A star-forming globule imaged in visible --gt
infrared light. Dust-shrouded new stars are
revealed in infrared image.
21
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.
22
In the heart of the Orion Nebula
23
In the heart of the Orion Nebula
24
(No Transcript)
25
(No Transcript)
26
Flying through the center of the Orion Nebula
27
(No Transcript)
28
(No Transcript)
29
A rotating proto-solar nebula rocks seem to be
the seeds of planets
30
Supernovae seed the interstellar gas with heavy
elements, which are the ashes of nuclear
burning. They come from massive stars, above 8
solar masses.
31
Order these star clusters by age
32
A major recent discovery color bimodality
33
A major recent discovery color bimodality
34
A major recent discovery color bimodality