Transcript The Life of a Star - Department of Physics and Astronomy

Astronomy: The Universe
HONORS 227 FALL 2005
20 October 2005
Dr. Harold Geller
From the past...
• “…How is it possible by any methods
of observation yet known to the
astronomer to learn anything about the
universe as a whole? It is possible
only because the universe, vast though
it is, shows certain characteristics of a
unified and bounded whole. …science
shows unity in the whole structure, and
diversity only in details.”
» Simon Newcomb, 1906
What I’m Going to Talk About
•
•
•
•
•
•
•
The Sky Tonight
Where did it all come from
The Big Bang
The life cycle of stars
The source of a star’s power
The death of stars
The chemical elements from stars
The Sky Tonight (20oct05)
The Brightest Stars in Our Skies
Common
Name
Sun
Sirius
Canopus
Rigil
Kentaurus
Arcturus
Vega
Capella
Scientific
Name
Sol
Alpha CMa
Alpha Car
Alpha Cen
Distance
(light years)
1.5 x 10-5
8.6
74
4.3
Apparent
Magnitude
-26.72
-1.46
-0.72
-0.27
Absolute
Magnitude
4.8
1.4
-2.5
4.4
Spectral
Type
G2V
A1Vm
A9II
G2V + K1V
Alpha Boo
Alpha Lyr
Alpha Aur
34
25
41
-0.04
0.03
0.08
0.2
0.6
0.4
Rigel
Procyon
Achernar
Betelgeuse
Hadar
Acrux
Beta Ori
Alpha CMi
Alpha Eri
Alpha Ori
Beta Cen
Alpha Cru
~1400
11.4
69
~1400
320
510
0.12
0.38
0.46
0.50 (var.)
0.61 (var.)
0.76
-8.1
2.6
-1.3
-7.2
-4.4
-4.6
Altair
Aldebaran
Antares
Spica
Pollux
Fomalhaut
Becrux
Deneb
Regulus
Adhara
Alpha Aql
Alpha Tau
Alpha Sco
Alpha Vir
Beta Gem
Alpha PsA
Beta Cru
Alpha Cyg
Alpha Leo
Epsilon
CMa
Alpha Gem
Gamma Cru
Lambda Sco
16
60
~520
220
40
22
460
1500
69
570
0.77
0.85
0.96
0.98
1.14
1.16
1.25
1.25
1.35
1.50
2.3
-0.3
-5.2
-3.2
0.7
2.0
-4.7
-7.2
-0.3
-4.8
K1.5IIIp
A0Va
G6III +
G2III
B81ae
F5IV-V
B3Vnp
M2Iab
B1III
B0.5Iv +
B1Vn
A7Vn
K5III
M1.5Iab
B1V
K0IIIb
A3Va
B0.5III
A2Ia
B7Vn
B2II
49
120
330
1.57
1.63 (var.)
1.63 (var.)
0.5
-1.2
-3.5
A1V + A2V
M3.5III
B1.5IV
Castor
Gacrux
Shaula
(var.)
(var.)
(var.)
(var.)
Interpreting the Table
• Distance
– In light years
• Apparent Magnitude
– Brightness as seen from Earth
• Absolute Magnitude
– Luminosity or brightness if ALL stars at 10pc
• Spectral Type (example for Sun which is G2V)
– G is spectral class
– 2 is spectral sub-class
• With spectral class leads to specific surface temperature
– V is luminosity class
• Giant (I, II III), sub-giant (IV) or main sequence (V)
– Main sequence is defined as hydrogen core fusion
Where Stars Came From:
The Big Bang
• The name “Big Bang” itself
– Given by Fred Hoyle to mock the original
theory formalized by George Gamow in a
discussion on radio in the early 1950s
• Common MISCONCEPTIONS
– An explosion like any other
– We can picture it from outside
– It gave off a sound like an ordinary explosion
What Came from the Big Bang
•
•
•
•
•
•
•
•
•
•
•
•
•
•
(Higgs Fields?)
(Strings?)
Radiation
Particles
Electron / Positron
Particle/Anti-particle Interactions
Inflation
Spontaneous Symmetry Breaking
Cosmos / Universe Gravity
Strong Force
Quarks
Proton
Neutron
Nuclear Fusion
Alpha Radioactivity
Beta Radioactivity
Atoms
Gases, liquids, solids
Electric Charge
Magnetism
Cosmic Background Radiation
Dark Matter
Dark Energy
Life
You and me
Physics of the Universe
• Space, Time, Matter and Forces
• Types of Matter
– Quarks -> Baryons
• protons, neutrons
– Electrons -> Leptons
• electrons, neutrinos, muons
• Types of Forces
– gravity, electromagnetism, strong, weak
Measurements of Doppler Shift
• A change in measured frequency caused
by the motion of the observer or the
source
– classical example of pitch of train coming
towards you and moving away
Hubble’s Law Derived from
Observations of Galaxies
• The further away a galaxy is, the greater
its recessional velocity and the greater its
spectral red shift
Concluding from Hubble’s Law
• From Hubble’s Law we can calculate a
time in the past when universe was a point
– Simple but not all that easy
• Big bang occurred about 14 billion years
ago
– big bang first proposed by Gamow based
upon such evidence
• Foretold of evidence of cosmic microwave
background and distribution of chemical elements
in universe
The Vacuum Era
• The Planck Epoch
– <10-43 sec. and about 1019 GeV (1 GeV = ~1013K)
– we just don’t know
• The Inflationary Epoch
– >10-43 sec., < 10-10 sec.
– expansion driven by “repulsive gravity”
The Radiation Era
•
•
•
•
•
•
•
Creation of light
Creation of baryonic matter
Electroweak epoch
Strong epoch
Decoupling of weak interaction
Creation of nuclei of the light elements
Decoupling of radiation spectrum
The Matter Era
• Transition from radiation domination to
matter domination
• Last scattering
• Dark Ages
• Galaxy Formation Epoch
• Bright Ages
The Degenerate Dark Era
• Whither the future?
– death of stars
– black hole domination
– black holes combine
• What’s Next?
– discussion held to another time
Summary of the Universe’s Timescale
Era
The Vacuum Era
Epochs
Main Event
Planck Epoch
Quantum
Inflationary Epoch fluctuation
Inflation
Time after bang
<10-43 sec.
<10-10 sec.
The Radiation Era Electroweak Epoch Formation of
Strong Epoch
leptons, bosons,
Decoupling
hydrogen, helium
and deuterium
The Matter Era
Galaxy Epoch
Galaxy formation
Stellar Epoch
Stellar birth
10-10 sec.
10-4 sec.
1 sec. - 1 month
The Degenerate
Dark Era
20-100 billion yrs.
100 billion - ????
Dead Star Epoch
Black Hole Epoch
Death of stars
Black holes
engulf?
1-2 billion years
2-15 billion years
The Evidence So Far
• Evidence for a “Big Bang”
– expansion of the universe
• galaxies receding from us
– everywhere the same (homogeneous and isotropic)
– remnants of the energy from the “Big Bang”
• a very hot body that has cooled
– 2.7 K cosmic background radiation
– the primordial abundance of chemical
elements
Cosmic Microwave Background
• How hot would the
cosmic background
radiation be
– close to 3 K
• first noticed by Penzias
and Wilson
– Got Nobel Prize
• interpreted by Dicke
– Didn’t get Nobel Prize
• confirmed by COBE
satellite
• again confirmed by
WMAP
Putting it into context
• Taking the
perspective of
the universe
with you at the
center
The CMB remainder
• Using COBE DIRBE data for examining
the fine differences
– fine structure of the universe
• led to the galaxies and their location
To WMAP and Galaxies
Types of Galaxies
(established by
Hubble)
• Spiral
• Barred Spiral
• Elliptical
• Irregular
Understanding the aging of stars requires both
observation and application of physical principles
• Because stars shine by thermonuclear
fusion of a fuel (hydrogen, etc.), they have
a finite life span – they do not live forever
• The theory of stellar evolution (bad name,
really the life cycle of stars, or the
development of stars) describes how stars
form and change during their life span
The Life Story of Stars
• Gravity squeezes
• Pressure forces resist
– Kinetic pressure of hot gases
– Repulsion from Pauli exclusion
principle for electrons - white dwarf
– Repulsion from Pauli exclusion
principle for neutrons - neutron star
– None equal to gravity - black hole
• Energy loss decreases
pressure
• Energy generation replaces
losses
• Star is “dead” when energy
generation stops
– White dwarf, neutron star, black hole
Luminosity
Surface
Gravity
Weight of outer layers
Gas
Pressure
Thermal
Energy
Center
The Spectral Measure of Stars Wien’s and Stefan-Boltzmann’s Laws
The HertzsprungRussell (HR)
Diagram
Interstellar gas and dust pervade the galaxy
• Interstellar gas and dust, which
make up the interstellar medium,
are concentrated in the disk of the
Galaxy
• Clouds within the interstellar
medium are called nebulae
• Dark nebulae are so dense that
they are opaque
• They appear as dark blots against a
background of distant stars
• Emission nebulae, or H II regions,
are glowing, ionized clouds of gas
• Emission nebulae are powered by
ultraviolet light that they absorb
from nearby hot stars
• Reflection nebulae are produced
when starlight is reflected from dust
grains in the interstellar medium,
producing a characteristic bluish
glow
Interlude – Up in the Sky Tonight
Protostars form in cold, dark nebulae
• Star formation begins in
dense, cold nebulae,
where gravitational
attraction causes a clump
of material to condense
into a protostar
• As a protostar grows by
the gravitational accretion
of gases, KelvinHelmholtz contraction
causes it to heat and
begin glowing
The more massive the protostar, the
more rapidly it evolves
Protostars evolve into main-sequence stars
• A protostar’s relatively
low temperature and
high luminosity place it
in the upper right region
on an H-R diagram
• Further evolution of a
protostar causes it to
move toward the main
sequence on the H-R
diagram
• When its core
temperatures become
high enough to ignite
steady hydrogen
burning, it becomes a
main sequence star
Interlude - Humor
• “OK stellar recruits, it’s time to learn what’s
really in store for you! I know that before you
signed up to be a massive star you read the
fancy brochures that talked about how brightly
you’d be shining and how you’d be visible from
halfway across the galaxy. But you mo-rons
must not have bothered to read the fine print
that said that you’d explode in seven million
years! And if you did read it then you’re even
stupider than you look. Seven million is not a
long time!”
» Eric Schulman [A Briefer History of Time]
Young star clusters give insight into star
formation and evolution
• Newborn stars may form
an open or galactic
cluster
• Stars are held together in
such a cluster by gravity
• Occasionally a star
moving more rapidly than
average will escape, or
leave the cluster
• A stellar association is a
group of newborn stars
that are moving apart so
rapidly that their
gravitational attraction for
one another cannot pull
them into orbit about one
another
• Star-forming regions
appear when a giant
molecular cloud is
compressed
• This can be caused
by the cloud’s
passage through one
of the spiral arms of
our galaxy, by a
supernova explosion,
or by other
mechanisms
Supernovae compress the interstellar medium
and can trigger star birth
A star’s lifetime on the main sequence is
proportional to its mass divided by its luminosity
• The duration of a star’s main sequence lifetime depends
on the amount of hydrogen in the star’s core and the rate
at which the hydrogen is consumed
• The more massive a star, the shorter is its mainsequence lifetime
The Sun has been a main-sequence star for about 4.56 billion years
and should remain one for about another 7 billion years
During a star’s main-sequence lifetime, the star expands somewhat
and undergoes a modest increase in luminosity
When core hydrogen fusion ceases, a mainsequence star becomes a red giant
Red Giants
• Core hydrogen fusion
ceases when the
hydrogen has been
exhausted in the core of a
main-sequence star
• This leaves a core of
nearly pure helium
surrounded by a shell
through which hydrogen
fusion works its way
outward in the star
• The core shrinks and
becomes hotter, while the
star’s outer layers expand
and cool
• The result is a red giant
star
Fusion of helium into carbon and oxygen begins at
the center of a red giant
• When the central temperature of a red giant reaches about 100 million K,
helium fusion begins in the core
• This process, also called the triple alpha process, converts helium to carbon
and oxygen
• H-R diagrams and
observations of
star clusters
reveal how red
giants develop
• The age of a star
cluster can be
estimated by
plotting its stars on
an H-R diagram
As a cluster ages, the main sequence erodes away from
the upper left as stars of progressively smaller mass evolve
into red giants
Planetary Nebulae – Death of a
Solar Mass Star
Planetary Nebula - NGC 7293
450 light years away in Aquarius
Planetary Nebula - NGC 7027
3000 light years away in Cygnus
Aging from Giants to Dwarfs
White Dwarf
Properties
Sirius A
Sirius B - WD
Property
Earth
Sirius B
Su n
Mass (Msun)
3x10
-6
0 .9 4
1 .0 0
0 .0 0 9
0 .0 0 8
1 .0 0
Luminosity (Lsun)
0 .0
0.0028
1 .0 0
Surface temperature (K)
287
27,000
5770
6
1 .4 1
Radius (Rsun)
3
Mean density (g/cm )
Central temp (K)
3
Central density (g/cm )
5 .5
2.8x10
4200
2.2x10
9 .6
3.3x10
7
7
7
1.6x10
160
Life Cycle by Mass from the
Main Sequence
Main sequence stars
Supergiants
Giants
Helium flash
C detonation
Heavy nuclei fusion
Supernovae
Planetary nebulae
Black holes
Ns
White dwarfs
100
40
10
4.0
Mass (MSun = 1)
1.0
0.4
0.1
A Massive Star (~25 Msun)
SN 1987A Outburst
Large Magellanic Cloud
February 23, 1987
Progenitor star was a blue
supergiant of about 20 Msun
Crab Nebula - 1054 A.D.
Neutron star
Copyright © Periodic Table of the Elements, Los Alamos National Laboratories
© Periodic Table of the Elements
Los Alamos National Laboratories
There are 92 elements produced naturally. Aside from
hydrogen, helium and a little lithium, they were all
produced BY THE STARS.
References (Books)
• Hogan, Craig (1997). The Little Book of the Big Bang,
Copernicus Springer-Verlag.
• Adams, Fred and Greg Laughlin (1999). The Five Ages
of the Universe, The Free Press.
• Schulman, Eric (1999). A Briefer History of Time, W.H.
Freeman and Company.
• Chaisson, E. and S. McMillan (1999). Astronomy Today,
Prentice Hall.
• Freedman, R.A. and Kaufmann, W.J. (2004). Universe,
7th edition, W.H. Freeman and Company.
• Seeds, M. (1998). Horizons, Exploring the Universe,
Fifth Edition, Wadsworth Publishing Co.
References (World Wide Web)
• Web pages for general information and other links
– http://physics.gmu.edu/~hgeller/
• http://antwrp.gsfc.nasa.gov/apod/astropix.html
– astronomy picture of the day
• http://itss.raytheon.com/cafe/cafe.html
– the astronomy café (reference and questions)
• http://physics.gmu.edu/~jevans/astr103/astr103.html
– Introductory astronomy with John Evans
• http://physics.gmu.edu/~jevans/astr328/astr328.html
– Introductory astrophysics with John Evans
• http://genesismission.jpl.nasa.gov/
– NASA Genesis Mission
• H-R Diagram Software
– http://www.cvc.org/astronomy/freeware.htm
• Stellar Evolution Software
– http://leo.astronomy.cz/sclock/sclock.html
Acknowledgements
• Thanks to my colleagues in the Department of
Physics and Astronomy including Maria
Dworzecka, Bob Ehrlich, Bob Ellsworth, John
Evans, Menas Kafatos, Jean Mielczarek, Rita
Sambruna, Indu Satija, Shobita Satayapal, Mike
Summers, John Wallin, Joe Weingartner.
• Also thanks to W.H. Freeman Company,
Prentice-Hall, American Institute of Physics
History Center, NASA Genesis Mission EPO,
NASA JPL, NASA STScI, and NASA GSFC.