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Black holes
A star’s internal struggle:
Inward crush of gravity
vs.
Outward push of
thermal pressure
For most of its life,
thermal pressure
keeps gravity at bay
The star heats, expands, reddens and
becomes a ……
red giant star
Red giant stars are
running out of
Hydrogen fuel and they
start to expand and cool
Eventually fuel for fusion runs out, star dies.
The fate of the stellar corpse lies in a final
battle between gravity and pressure
Degeneracy Pressure
• Subatomic particles become packed as
close together as the laws of quantum
mechanics will allow
• White dwarfs & neutron stars are called
“degenerate objects”, and are made of
“degenerate matter
• Gravity and not strong force holds them
together
Degeneracy Pressure
• Density of a star 1.4 x mass of sun would
weigh 5 tons per teaspoon
• Density of a star 3x mass of sun a
paperclip would weigh as much as Mt.
Everest.
Degeneracy Pressure
• White dwarfs: electron degeneracy
pressure
• Neutron stars : neutron degeneracy
pressure
If Gravity wins over pressure,
stellar corpse keeps collapsing
without end, crushing itself out
of existence
Forming a Black Hole
Gravity’s
Ultimate
Victory!
The idea of Black Holes
is not new!
It was first proposed by
John Mitchell and Pierre
LaPlace in the 1700’s
The
boundary
between
the black
hole and
the
universe is
called the
Event
Horizon
There is no way to get
information about
events happening
beyond the Event
Horizon
The escape
velocity out
of the black
hole is
greater than
the speed
of light
Light always follows the
straightest path through
spacetime
Since
spacetime
near a
black hole
is curved,
light curves
What is inside a black
hole?
The mass of
the dead star’s
core, but there
would be no
recognizable
remains.
Since stars rotate, the
black hole probably also
rotates to conserve
angular momentum
Black holes
appear to have
a neutral
charge
Black Holes Don’t “suck”!
1. If our sun became a black hole, we would
get no more heat or light from it, but our
elliptical orbit would not change.
2. We would not be “sucked in”
3. Spaceships near a black hole would
merely go into orbit around it
4. Black Holes are so small it would be hard
to “fall in” by accident
The Singularity
1. The center of the black hole
2. Gravity crushes all matter into an
infinitely tiny and dense point
3. General Relativity says that spacetime
grows infinitely curved there
4. Quantum Physics says that spacetime
fluctuates chaotically there
A gold mine for science fiction!
Are black holes real?
We have only detected
them indirectly since
they can’t be seen
But the theory is
scientifically solid
“Now my suspicion is
that the universe is not
only stranger than we
suppose….
…but stranger than
we can suppose.”
-JBS Haldane, 1927