Download Presentation

Stellar Evolution
Marielle Deconinck
2
Outline
I Birth of a Star
-stellar nurseries
II Life of a Star
-protostars
-main sequence stars
III Death of a Star
-white and black dwarfs
-supernovae
-neutron stars
-black holes
Marielle Deconinck
3
Brief History of Stellar Observation
• Religion, celestial navigation, orientation,
calendars
• Oldest accurate star chart  ancient Egypt,
1534 BC
• Lascaux Paleolithic
cave paintings,
circa 17,300 years
ago
BBC News
Marielle Deconinck
4
What is a Star?
• Sphere of plasma
Lifetime of Stars as a Function of
their Masses (logarithmic scale)
• Form a star cluster
or galaxy
• Vary with mass
• Main source of
energy  nuclear
fusion
Lifetime (Million Years)
10000
1000
100
10
1
1
1.5
3
10
Mass (Solar Mass)
30
60
Marielle Deconinck
1.98855×1030 kg
The Sun
3.828×1026 W
6.95700×108 m
5,777 K
• Yellow dwarf
• Magnetic field
• 99.9% of total mass of
Solar System
• 70 % Hydrogen,
28 % Helium,
1.5 % Carbon, Nitrogen,
Oxygen
0.5 % Other Elements
NASA/SDO
Marielle Deconinck
5
6
Birth of a Star – Stellar Nurseries
• Dense regions in molecular
clouds (>one million particles
per cm3)
• If the cloud is big enough, it
will undergo gravitational
collapse
Protostars
NASA/JPL-Caltech/W. Reach (SSC/Caltech)
Marielle Deconinck
7
Protostars
Continue to grow by accretion of gas and dust
Mass < 0.08 M☉
Core temperature
reaches 10 million K
Proton-proton chain
reaction initiated allowing
H to fuse to 2H, then to He
Temperature too low for
nuclear fusion of H
Brown dwarf
Main sequence star
Marielle Deconinck
8
Main Sequence Stars
Hertzsprung-Russell
Diagram (1910)
Relationship between
luminosity and effective
surface temperature
Small, cold stars stay for
hundreds of billions of
years
Massive, hot stars will
leave after a few million
years
Richard Powell
Marielle Deconinck
9
Death of a Star
No more nuclear fusion  no force to counteract force
of gravity  collapse
Depending on mass, 3 possible outcomes:
1) White and Black Dwarf
2) Neutron Star
1) Black Hole
Marielle Deconinck
10
White and Black Dwarfs
Sirius A
Over 100,000 K at surface
Small (< 0.5 M☉ )  mainly He
Medium (around 1 M☉ )  C, O
NASA, ESA, H. Bond (STScI) and M. Barstow
(University of Leicester)
Large (> 1 M☉ )  mainly O, Ne, Mg
Radiates heat until all energy is used up
Black Dwarf
Marielle Deconinck
11
Neutron Stars
Stellar core collapses,
electrons and protons fuse
Electron capture:
p + e− → n + νe
 Neutrons collapse into a dense ball
• Extremely small
(10 km radius)
• Extremely dense
(1017 kg/m3)
• Extremely short rotation
period (1.5 ms)
NASA/Andrew Fruchter (STScI)
Marielle Deconinck
12
Supernovae
http://www.novacelestia.com/images/stars_supernova_process_medium.jpg
Marielle Deconinck
13
Black Holes
Escape velocity from the surface of the star > speed of light
(gravitational radius)
Extremely high mass  neutron degeneracy
pressure insufficient to prevent collapse below
gravitational radius
(NASA/Dana Berry/SkyWorks Digital)
Marielle Deconinck
14
References
Books:
Carlos A. Bertulani –
http://www.worldscientific.com/worldscibooks/10.1142/8573
Longair, M. S. (2008). Galaxy Formation (2nd
ed.). Springer. p. 478.
Prialnik, Dina (2000). An Introduction to the Theory of Stellar
Structure and Evolution. Cambridge University Press.
Stahler, S. W. & Palla, F. (2004). The Formation
of Stars. Weinheim: Wiley-VCH.
Websites:
http://science.nationalgeographic.com/science/space/solarsystem/neutron-stars/
NASA/SDO:
http://sdo.gsfc.nasa.gov/assets/img/browse/2010/08/19/20100819_0
03221_4096_0304.jpg
Marielle Deconinck
15
Summary
Marielle Deconinck