Transcript Life Cycles of Stars

The Life Cycles of Stars
RVCC Planetarium - Last updated 7/23/03
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Stars have
• Different colors
 Which indicate different temperatures
• Different sizes
• Different masses
The bigger it is, the hotter and the
faster a star burns its life away.
Stellar Evolution
Stars begin
their lives as
clouds of gas
and dust
called Nebulas
Clouds
Contain:
•70% H
•28% He
•2% Heavier
Elements
Stars start from Nebula Clouds
Collapse to Protostar
• Nebula compresses
• Gravitational pull attracts more material.
• Temperature and pressure increases
• Nebula shrinks and begins to spin
• Spinning nebula begins to flatten into a
disk
….A protostar is formed
Protostars are forming in Orion
Protostars
are forming
in the Orion
Nebula
•Pressure builds inside the protostar over
millions of years creating heat
•Temp increases to 10 million°C
•Nuclear fusion begins….A star is born!!
•Main Sequence stage of a star begins
•It is the longest stage in life of a star
Nuclear Fusion !
• At 15 million degrees Celsius in the center
of the star, Hydrogen Atoms fuses into
Helium.
• It takes 4 Hydrogen atoms to make one
Helium atom
• Sun has 1056 H atoms to burn which would
last 8 billions year!
The Beginning of the End: Red Giants
After Hydrogen is exhausted in core:
• Core collapses, releasing energy to the
outer layers
• Outer layers expand
The Core of a Red Giant
•Giants are 10 times bigger than the sun
•Supergiants are 100 times bigger than the sun
Expansion of the outer Layers
Betelgeuse – A Red Giant Star
Outer Layers are Expelled …
… And a Planetary Nebula forms
After Helium exhausted, outer layers of star expelled
Planetary Nebulae
Some Planetary Nebulae are Round
As the dead core of
the star cools, the
nebula continues to
expand, and
dissipates into the
surroundings.
… and Bipolar
Some look like an Hourglass …
.. or a Cat’s Eye …
… or even look like an Eskimo!
White Dwarfs
At Center of a Planetary Nebula …
… sits a White Dwarfs
White dwarfs shine for
billions of years before
they cool completely.
The Hubble Space Telescope has detected
white dwarf stars (circled) in globular clusters:
White Dwarfs are Small and Heavy
Size of the Earth with the Mass of the Sun
“A ton per teaspoon”
Nova is a
white dwarf
star that
suddenly
increases in
brightness by
several
magnitudes.
It fades very
slowly.
Fate of High Mass Stars
• After Helium is exhausted, core collapses
again until it becomes hot enough to fuse
Carbon into Magnesium or Oxygen.
• Through a combination of processes,
successively heavier elements are formed
and burned.
The End of the Line for Massive Stars
• Massive stars
burn a
succession of
elements.
• Iron is the most
stable element
and cannot be
fused further.
A Massive Star Explodes
A Supernova is
an exploding
massive star
Supernova 1987a
What’s Left After the Supernova
Neutron Star (If mass of core < 5)
• Under collapse, protons and electrons
combine to form neutrons.
Black Hole (If mass of core > 5)
• The force of contraction crushes the
dense core of the star
• The gravity of a black hole is so great
that not even light can escape from it.
Supernova interaction
Supernovae compress
gas and dust which lie
between the stars.
This compression starts
the collapse of gas and
dust to form new stars.
Which brings us back to …
Stellar Recycling
Supergiant
Red
Giant
Low mass main
sequence star
Protostar
Planetary
Nebula
High mass
main sequence
star
Nebula
Supernova
Neutron Star
White Dwarf
Nova
Black Hole
Sun-like Stars
Massive Stars