Transcript Evolution and the Big Bang, ET Life Lec. 6, Jan 18, 2002

Alchemy of The Heavens
View, low in
the East, early
in the morning
of July 5,
1054 shows
the Crab
Supernova
Lecture Eight, Feb. 3, 2003
Columbia’s Final Flight
8:53 a.m. Shuttle had just
completed a roll reversal,
a procedure to bleed
energy before landing.
Four left wing temperature
sensor readings in the
hydraulic system
suddenly were lost.
8:56 a.m. Sensors in
main left wheel well failed,
and tire temperatures
were not available. Shuttle
was performing well
otherwise.
8:58 a.m. Three left wing temperature
sensor readings are lost. Because sensors
are independent and not linked to a
common avionics box, Mission Control
becomes concerned.
8:59 a.m. Eight tire temperature and
pressure readings are lost. An on board
alert message is sent to the crew. In their
last transmission, crew members said they
had received the alert.
9 a.m. All communication with the shuttle is
lost.
Alchemy of The Heavens
• How did God make the chemical elements?
• Chemical element has atomic number Z
(number of electrons orbiting nucleus).
• Chemical reactions do not change the # or
type of atomic nuclei. Many alchemists
tried and failed to convert Lead (Z=82) into
Gold (Z=79).
Big Bang Nucleosynthesis
• Nucleosynthesis: origin of the atomic nuclei, (which
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capture electrons to form chemical elements).
Nuclei are made of protons and neutrons. These
particles have similar mass but only protons have an
electric charge.
Protons and neutrons are each made of three quarks.
By about 3 min. after Big Bang all of the neutrons are
bound into 4He nuclei which have two protons (Helium
has Z=2) and 2 neutrons.
Remaining protons are free to form Hydrogen (Z=1).
Thus Universe was about 25% He and 75% H and little
heavier elements (those with Z>2).
Early Stars
• First generation stars were
made out of only H and He.
• Even if they had planets there
was no Si (Z=14) for rocks, no
O (Z=8) for H2O and no C
(Z=6) for life. Planets would
be gas balls like our gas
giants.
• Need to make these elements
with nuclear reactions in first
generation stars.
There could not be rocky planets
like Jupiter’s Moons (above) but
only gas balls like Jupiter (below).
Nuclear Reactions
• Can make new nuclei.
• However, nuclei are normally kept apart by
strong electric repulsion.
• Need great heat and or density to
overcome this repulsion and allow nuclear
rxns.
• These extreme conditions are reached in
the center of normal stars.
How to get new elements out?
• Problem, nuclear rxns, in general, only
take place deep within a star. Thus the
new elements are locked deep in the stars
core.
• How to get the elements out to form rocky
planets and life?
• Answer: Wait for the star to die.
Life of a Star
• Birth: collapse of gas cloud forms protostar.
• Main sequence: center of star becomes hot
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enough to burn Hydrogen into Helium. Our Sun
will be on main sequence for 10 billion years.
Red Giant: Outer part of star expands and
cools. Core contracts and starts to burn He into
Carbon and other heavier elements.
Star dies: either as a planetary nebula (low mass
star) or as a supernova (high mass star).
Planetary Nebula
• Stars with mass less then about 8 times the
mass of the Sun die as planetary nebula.
• Intense stellar wind ejects lots of gas from
surface of red giant. Note, Sun has solar
wind which is stream of particles from
surface.
• Note, planetary nebula name has nothing to
do with planets.
Planetary Nebula M27
Image by J. Newton
Jack Newton’s House
Furniture salesman and amateur astronomer
The Universe From My Driveway
• On the course web site I
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have added some images
taken with a small 8”
telescope and a sensitive
CCD camera.
http://physics.indiana.edu
/~life and click on
driveway universe.
One evening during the
class, those interested
can observe with me.
Supernova
• Stars with more then 8 solar masses die in
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gigantic explosions called supernovae. Note,
plural of supernova is supernovae.
A single star that explodes as a supernova can
outshine an entire galaxy (billions of stars).
Hard to imagine the violence of the explosion.
Core of star imploded to form neutron star or
black hole.
Outer part of star ejected into space with new
chemical elements.
Supernova viewed from my
driveway
SN1998S in Ngc 3877, April 2, 1998 (8” SCT
homemade CCD)
A Supernova is very bright
• Note, foreground stars are typically 100s
of light years away.
• Galaxy and supernova are ~100 million
light years away.
• That one can see it at all implies the
explosion is very bright.
Supernova Simulation
• Computer simulation by
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Adam Burrows of a
supernova in a binary star
system (two stars orbiting
each other).
You are looking at the 2nd
star which is many times
larger then the Earth.
The exploding star is just
off the top of the screen.
Real Video of Burrows
Simulation
The Crab Supernova
Moon
Supernova
Simulation of view early in the morning, July 5, 1054
Native American Paintings of Crab
• Well recorded in China, Korea and Middle East but not in
Europe (middle ages).
Crab Nebula Today
• Exploding star has
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thrown material out
into space at about
1/300 speed of light.
In 1000 years nebula
is now about 3 light
years across.
Nebula enriches
interstellar medium
with chemical
elements.
Vela: 10000 year old SN Remnant
Vela
Pulsar
Crab pulsar
• Hubble space
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telescope image (in
visible light) of
neutron star (base of
arrow) at heart of
Crab nebula.
Neutron star spins 30
times a second and
emits pulses of radio
waves  pulsar.
Neutron Star
• Collapsed object 1.5
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times mass of Sun but
only about 10 miles
across. It is one gigantic
atomic nucleus!
Squeeze all of the empty
space out of an atom.
Squeeze electrons onto
protons to form neutrons.
Gives neutron star.
Densest form of matter
before black hole.
Supernovae
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Gigantic stellar explosions.
Eject new chemical elements into space.
Make neutron stars and black holes.
Accelerate cosmic rays (energetic particles
constantly hitting Earth’s atmosphere from
space).
Shock waves can help gas clouds to collapse and
form new stars.
Deadly to life (within say ~1-300 light years???)
2nd Generation Stars
• 2nd generation stars, made from the collapse of
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a gas cloud enriched in chemical elements, can
have rocky planets and perhaps life.
Sun formed 4.6 Billion years ago.
Needed 1st generation stars to be formed, live,
and die all before 4.6 Billion years ago.
These provided the Carbon, Oxygen, Nitrogen …
of which we are made.
We are literally “star dust”. All of the atoms in
our body were made in other stars.
For next time
• Read chap. 4 of Jakosky about the earliest
life and read “Vital Dust", pages 1-23 in
course packet about origin of life.
• Next lecture, Wend Feb 5, 2003,
“Formation of Earth”.