The Past and Future History of

the Sun

Mini-University 2004

Outline

• 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

• 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 existenceVery smallVery 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?

The Eta Carina Nebula has some of the Milky Way’s most massive stars

Stars are forming

continuously in the Galaxy

Star Formation!

Examining a Star Forming Region

Stars are born in cold, dense interstellar clouds

• cold gas• dust grains

The Great Nebulain Orion

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

FormingRegion

Young stars are surrounded by dense disks of gas and dust

Disks have been imaged

with HST’s infrared camera

Basic facts:• 2-4 million years old• about 469 light-years distant• The disk is about 30 times the size of our solar systemWhy the window

pane appearance?

HST

Swirling disks around the

youngest starsThe 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

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

A young star in the Rho Ophiuchus dark cloud

Infrared false-color image from the ESO Antu telescope

Dust grains

form around the young star

Isotopes in the Pre-Solar Nebula

• Small mineral grains in meteorites contain evidence of long-decayed 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 explosion Formed 4,700,000,000 years ago

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-isotopeHalf Life(years)

DaughterIsotope

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 light-year

– 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

The Sun’s Outer Atmosphere:

The Chromosphere and Corona

• Temperatures over a million degrees

• Magnetic fields• The solar wind

The Chromosphereis red because of emission from the hydrogen alpha line

dense jets of gas that shoot up from the

chromosphere

coronal

hole

The Corona is the outer layer of the Sun’s atmosphere, with a temperature of a million degrees or more

The corona is heated by the

twisting loops of magnetic field

massejectio

n

The Solar Magnetic Field

Listen to the Sun

Looking insidethe 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

everythingelse

90% hydrogen atoms

10% helium atoms

Less than 1% everything else(and everythingelse is made in stars!)

The Sun’s Energy Comes from Nuclear Fusion

Watching the Far Side of the Sun

The Sun in Time

n

The Sun in Time

Luminosity of the Sun

0

1

2

3

4

5

0 2 4 6 8 10 12Time since Formation (Billions of Years)

Bri

gh

tne

ss

The Sun is gradually growing brighter over time, as it converts helium into hydrogen

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

• the remaining cluster stars will scatterBigger stars are “too bright” to form

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

The Sun today

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 orbit of Venus

• 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

The End of the Red Giant Phase

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

The End of Sun-Like Stars

What about the Earth?

OrdinaryStar

RedGiant

PlanetaryNebula

White Dwarf

Fire and Ice!

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 happenedBig 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 ERAThe 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. Particle-antiparticle 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/