The Past and
Future
History of
the Sun
Mini-University 2004
• A brief history of the Universe
• The Sun’s Early History
– How do stars form?
– Isotopes in the pre-solar nebula
– The birth of the Sun
• The middle-aged Sun
– The star we know
– Looking inside the Sun
– The Sun in time
Outline
• As the Sun grows old
– Red giant
– Planetary nebula
– White dwarf
•
The distant future
A Brief
History of
the Universe
BIG BANG – 13.7 billion years ago, space,
time, and energy burst into existence
Very small
Very dense
Why?
INFLATION ERA – the universe explodes from smaller than
an atom to the size of a grapefruit. Expansion slows when
the driving force is transformed into matter and energy
Because all of space was so compact, every part
of the universe was in “contact” with every
other part.
Energy was uniformly distributed throughout
the early universe
PHOTON ERA - energy in the form of electromagnetic
radiation - visible light, X rays, radio waves and ultraviolet
rays. Energy transforms into matter:
•quarks
•protons and neutrons
•helium, deuterium and lithium
• The Universe was dominated by energy.
• The density of energy was so great that matter
could not exist.
• As the density was gradually reduced through
expansion, matter began to form.
• Both matter and anti-matter formed, but for some
reason, there was a slight excess of matter.
Origin of the Cosmic Microwave
Background Radiation – the glow of the
original, hot matter of the Universe
A uniform, faint
microwave signal all
over the sky
What are we seeing
in the baby picture?
 The microwave
radiation comes from
the time when the
temperature of the
Universe became low
enough for atoms to
form
 Matter became
transparent, allowing
light to travel great
distances
 It is like seeing the
bottom layer of clouds
on an overcast day.
STELLIFEROUS ERA – the current era
• Electrons combined with existing nuclei to form
atoms, mostly hydrogen and helium
• Atoms condensed into the first generation of
stars during the first 200 million years
• Galaxies formed
• Sun, solar system formed 4.6 billion years ago
• Life appeared on Earth 3.8 billion years ago
• Modern humans show up just 100,000 years ago
The Sun’s Early History
We know the Sun formed when
the Universe was already more
than 9 billion years old
How and why did the Sun form?
Star
Formation!
Stars are
forming
continuously
in the Galaxy
The Eta Carina Nebula has some of the Milky Way’s most massive stars
Examining a Star
Forming Region
The Great Nebula
in Orion
Stars are born in cold,
dense interstellar clouds
• cold gas
• dust grains
Star formation is triggered when an interstellar
cloud is compressed by a shock wave
•
•
•
•
collision with another cloud
nearby supernova explosion
nearby hot star wind
disturbance from the Galaxy
Free Fall
Contraction
As the cloud begins to
collapse, it fragments
into blobs that
contract into
individual stars.
The blobs glow faintly
in radio or microwave
light because they are
very cool.
They gradually heat
up as they contract
and begin to glow in
the infrared, but they
remain hidden in the
interstellar cloud.
The Cone
Nebula
Examining
a Star
Forming
Region
Disks have
been imaged
with HST’s
infrared
camera
Young stars are
surrounded by dense
disks of gas and dust
Swirling disks around
the youngest stars
HST
Basic facts:
• 2-4 million years old
• about 469 light-years distant
• The disk is about 30 times
the size of our solar system
Why the window pane
appearance?
The collapsing protostar
eventually heats up enough to
slow the collapse through
hydrostatic pressure, and
blows away its cocoon.
What’s left is a T Tauri star, in
the final stage of accretion of
gas.
The Flying
Saucer
A young star in the Rho
Ophiuchus dark cloud
Infrared false-color image
from the ESO Antu telescope
 Star forming region 500
LY from Earth
 Dark, dusty disk seen
edge-on
 About 300 AU across (or
5 times the diameter of
Neptune's orbit)
 Central star is unseen
Dust grains
form around
the young
star
Isotopes in the
Pre-Solar Nebula
• Small mineral grains in
meteorites contain
evidence of longdecayed radioactive
material
• The radioactive material
decayed, and left rare
forms of some elements
in the rock
26Aluminum
•13 protons
•13 neutrons
26Magnesium
•12 protons
•14 neutrons
When we find an
excess of 26Mg, we
know 26Al must have
been present
Half of the 26Al
decays each 740,000
years
The Earliest Pre-Solar Grains
• Calcium-aluminum-rich
inclusions
• Contains decay products
of 26Al
• Ratio of original
26Al/27Al ratio allows us
to date how long it took
for the grain to form
after the 26Al was
created in a supernova
Formed 4,700,000,000 years ago
explosion
Grains Continued to Form
• Chondrules (grains
found in primitive
meteorites) also
contain the “daughter
products” of decayed
26Al
• Chondrules formed
about 2 million years
AFTER the CAl rich
inclusions
Half life 740,000 years
Meteorites Once Contained
60Fe
• Troilite (FeS) grain
in the Bishunpur
meteorite
• Small nickel content
allows detection of
60Ni, which decays
from radioactive
60Fe
Half life 1.5 million years
Sun’s Formation
Triggered by
Supernova Explosion
• Radioactive material had to have
been formed in the explosion of a
massive star just before the Sun
formed
• Material from the supernova
explosion became incorporated
into the pre-solar nebula
Extinct Isotopes in Early Solar Nebula Rocks
Radio-isotope
Half Life
(years)
Daughter
Isotope
Reference
Isotope
41Ca
100,000
41K
40Ca
26Al
740,000
26Mg
27Al
10Be
1,500,000
10B
9Be
60Fe
1,500,000
60Ni
56Fe
The Birth of
the Sun
The Sun formed as part of a
modest-sized cluster of stars
A nearby massive star exploded,
creating radioactive elements
The explosion probably triggered
the formation of the Sun
The Birth of the Sun
• The young cluster Messier 103
– in direction of the
constellation Cassiopeia
– a distance of about 8000
light-years
– diameter of about 14 lightyear
– age of over 20 million years
old
The Middle-Aged Sun:
The Star We Know
The Visible “Surface” of the Sun
Sunspots
• cooler regions
• magnetic fields
• prominences originate
from active regions
• Temperatures over a million
degrees
The Sun’s Outer Atmosphere:
The Chromosphere and Corona • Magnetic fields
• The solar wind
The Chromosphere
is red because of
emission from the
hydrogen alpha line
dense jets of
gas that
shoot up
from the
chromospher
e
The Corona is the outer
layer of the Sun’s
atmosphere, with a
temperature of a million
degrees or more
coronal
hole
mass
ejectio
n
The corona is
heated by the
twisting loops of
magnetic field
The Solar
Magnetic Field
Looking inside
the Sun
Listen to the Sun:
Listen to the Sun
Helioseismology
With helioseismology,
we can measure
temperature, pressure
and motion inside the
Sun from sound waves
that traverse the Sun’s
interior.
Listen to the Sun
Inside the Sun:
Energy and Motion
The energy
comes from
nuclear fusion
reactions in
the Sun’s core
The Composition of the Sun
90% hydrogen atoms
10% helium atoms
Less than 1%
everything else
(and everything
else is made in stars!)
everything
else
The Sun’s Energy Comes from Nuclear Fusion
Watching
the Far Side
of the Sun
The Sun in Time
n
5
The Sun
in Time
Brightness
4
3
The Sun is
gradually growing
brighter over
time, as it
converts helium
into hydrogen
Luminosity of the Sun
2
1
0
0
2
4
6
8
10
Time since Formation (Billions of Years)
12
Eventually…
As the Sun Grows Old…
Stellar
Evolution –
Studying the
Lives of
Stars
• To learn about
the future of
the Sun, we
must study
other stars…
Stars
according to
Goldilocks
• The most massive stars form first
• Some stars have 100 times the mass of
the Sun
• Most stars are smaller than the Sun
• Stars lower than 0.08 solar mass (called
brown dwarfs) cannot fuse hydrogen and
simply cool off
Evolution of a Very Low Mass Star
๏
• Very low mass
stars (30% of
the mass of the
Sun), have
“lifetimes” of
100’s of billions
of years before
they consume
their hydrogen
The Most Massive Stars
• The biggest stars in the Milky Way “live” only a few
million years before using up their hydrogen
• Found in star clusters near the center of the Galaxy
• 2-4 million years
old
• masses more than
100 Suns
• they will explode
as supernovae
Bigger stars are “too bright” to form
• the remaining
cluster stars will
scatter
Evolution of a
Just-Right Star
• The Sun will burn its
hydrogen for about
10 billion years
before it runs out
• The hydrogen fusion
reactions take place
in the core
• When the hydrogen in
the core is used up
– the core SHRINKS
– the star EXPANDS!
The Sun Becomes a Red Giant
When the helium core contracts, the surrounding
hydrogen puffs up and the star becomes a red giant.
The Sun
as a
Red Giant
Astronomers aren’t sure how big the
Sun will grow when it becomes a red
giant. It may become as large as the
orbit of Venus, or even the Earth
The Sun today
The Sun as a red giant
The orbit of Venus
The End of the Red Giant Phase
• Eventually, the outer
layers blow off, exposing
the hot central core of
the star
• The hot central core
heats the escaping gas
and causes it to glow
• The central core
becomes a “white dwarf”
star, very dim and faint
Planetary
Nebulae!
What’s Left? A White Dwarf
•
•
•
•
About half the mass of the
Sun
• the other half is blown
away
The size of the Earth
Density of 1-2 tons per cubic
centimeter
Composed of carbon and
oxygen
• little or no hydrogen or
helium
Sirius B
Sirius in X-rays
Ordinary
Star
The End of SunLike Stars
Red
Giant
Planetary
Nebula
What about the Earth?
Fire and Ice!
White
Dwarf
If the Earth survives the red giant phase, then
our world will be come cold and dark.
The Evolution of Stars
The Universe in a Day
Event
When it happened
Big Bang
12:00:00 midnight
First Atoms form
12:00:08 a.m.
Stars and Galaxies form
12:29 a.m.
Our Sun, Earth, Moon are born
4:00 – 4:48 p.m.
Earliest life on Earth
6:00 p.m.
First multi-cellular life on Earth
10:53 p.m.
Dinosaurs appear
11:40 p.m.
Dinosaurs die
11:54 p.m.
Humans arise
11:59:56 p.m.
Present Day
12:00 midnight tomorrow
Sun becomes Red Giant
8:00:00 a.m. tomorrow
Sun becomes White Dwarf
8:19:00 a.m. tomorrow
DEGENERATE ERA –
10 trillion trillion trillion years after the Big Bang
• Planets detach from stars
• Stars and planets evaporate from
galaxies
• Most ordinary matter in the universe is
locked up in degenerate stellar remnants
• Eventually, even the protons themselves
decay
BLACK-HOLE ERA 10,000 trillion trillion trillion trillion trillion
trillion trillion trillion years after the Big
Bang
• The only large objects remaining are
black holes
• Eventually even the black holes
evaporate into photons and other types of
radiation.
The Final DARK ERA –
Only photons, neutrinos, electrons and positrons
remain, wandering through a universe bigger than
the mind can conceive.
Occasionally, electrons and positrons meet and
form "atoms" larger than the visible universe is
today.
From here into the infinite future, the universe
remains cold, dark and empty.
The History of the Universe in 200 Words or Less
Quantum fluctuation. Inflation. Expansion. Strong nuclear interaction. Particleantiparticle annihilation. Deuterium and helium production. Density perturbations.
Recombination. Blackbody radiation. Local contraction. Cluster formation.
Reionization? Violent relaxation. Virialization. Biased galaxy formation? Turbulent
fragmentation. Contraction. Ionization. Compression. Opaque hydrogen. Massive star
formation. Deuterium ignition. Hydrogen fusion. Hydrogen depletion. Core
contraction. Envelope expansion. Helium fusion. Carbon, oxygen, and silicon fusion.
Iron production. Implosion. Supernova explosion. Metals injection. Star formation.
Supernova explosions. Star formation. Condensation. Planetesimal accretion.
Planetary differentiation. Crust solidification. Volatile gas expulsion. Water
condensation. Water dissociation. Ozone production. Ultraviolet absorption.
Photosynthetic unicellular organisms. Oxidation. Mutation. Natural selection and
evolution. Respiration. Cell differentiation. Sexual reproduction. Fossilization. Land
exploration. Dinosaur extinction. Mammal expansion. Glaciation. Homo sapiens
manifestation. Animal domestication. Food surplus production. Civilization! Innovation.
Exploration. Religion. Warring nations. Empire creation and destruction. Exploration.
Colonization. Taxation without representation. Revolution. Constitution. Election.
Expansion. Industrialization. Rebellion. Emancipation Proclamation. Invention. Mass
production. Urbanization. Immigration. World conflagration. League of Nations.
Suffrage extension. Depression. World conflagration. Fission explosions. United
Nations. Space exploration. Assassinations. Lunar excursions. Resignation.
Computerization. World Trade Organization. Terrorism. Internet expansion.
Reunification. Dissolution. World-Wide Web creation. Composition. Extrapolation?
Copyright 1996-1997 by Eric Schulman .
Websites of Interest
 Indiana Astronomical Society
www.iasindy.org
 National Optical Astronomy Observatory Image
Gallery
www.noao.edu/image_gallery
 Hubble Space Telescope Images
www.hubblesite.org
 Amazing Space
amazing-space.stsci.edu
 NASA’s Astronomy Picture of the Day
antwrp.gsfc.nasa.gov
Astronomical Society of the Pacific
www.astrosociety.org
The Stonebelt Stargazers
www.mainbyte.com/stargazers/