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Stellar Evolution
Part 3
Fate of the most massive stars
A Star with a mass of at least 1.5 times that of the Sun
generates much higher Temperature and Pressure
in its core.
After less than a billion years…
it starts to run out of hydrogen in its core and fusion
slows:
Its core shrinks and gets hot enough to…
Fuse Hydrogen into Helium in a shell outside the core
Begin to fuse Helium into Carbon in its core
The star itself expands
The outer layers cool and it becomes a red supergiant
When it runs out of helium in its core
It shrinks
And heats up
Carbon begins to fuse into Neon in the core
While He→Carbon, and H→He in shells.
Each time it runs out of fuel in the core a new
reaction begins there and the former reaction
starts in a shell.
It gradually heats up becoming a Blue Supergiant
Eventually in the Core Silicon→Iron and outside the
core O→Silicon, Neon→O, Carbon→Neon,
He→Carbon, and H→He fuse in shells
Supernova!
Eventually the Star starts to run out of silicon in the core
Fusion slows and the star becomes a red supergiant again
Since Iron doesn’t release energy when it fuses,
It needs vast amounts of energy to fuse, so Fusion Stops.
The core shrinks rapidly in microseconds.
The Outer-layers crash inward superheating the core to
billions of degrees.
Iron and other elements fuse into heavy metals and
The Outer-layer bounce back
the Star Explodes…
A Supernova!
Nebulae
The Nebula
created by a
supernova
expands at
10,000 km
per second!
And is chaotic
in
appearance
Neutron Stars
The core of a star with between 1.5 and 3 solar
masses will collapse after the Supernova
It becomes so dense that Electrons meet protons and
charges cancel…
A Neutron Star
With a thin crust of Iron.
It begins to spin super-fast with a period is as little as
a second!
This generates a strong magnetic field and a beacon
of radio energy that acts like a spinning search-light.
That appear to us as a Pulsar, a source of a rhythmic
radio signal first thought to be intelligent aliens!
Black Holes
A star with 3x the sun’s mass or more has enough
mass so that when it collapses the gravitational field
becomes so strong that the escape velocity near it
becomes faster than light.
Light itself cannot escape….
A Black Hole.
The distance from the star called the Event Horizon is
where escape velocity is equal to light-speed.
Any closer and nothing can escape!
Black holes are detected by the infrared and X-ray
light produced by the whirlpool material falling into
the “hole”.