Transcript 10 relativity, black holes_

Agenda
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Types of star deaths
Relativity
Black holes
Evidence for both
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H runs out: star becomes a
red giant
Exterior expanding
H fusing
He core
contracting
Mass alone determines death
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Small mass: White
dwarf
Med. Mass: Neutron
star or pulsar
Large mass: Black hole
Determined by S. Chandreskhar
What type of death will our
Sun die?
What will happen to us?
Diameter (times present value)
Sun’s fate
Orbits of:
Mars
Earth
Venus
Mercury
100
10
Helium
shell
flashes
Contraction
Leaves Main
sequence
Now
1
0
5
First
Red giant
peak
White
dwarf
10 12.1 12.2 12.3 12.3650 12.3655
Age (billions of years)
Diameter (times present value)
Sun’s fate
Orbits of:
Mars
Earth
Venus
Mercury
100
10
Helium
shell
flashes
Contraction
Leaves Main
sequence
Now
1
0
5
First
Red giant
peak
White
dwarf
10 12.1 12.2 12.3 12.3650 12.3655
Age (billions of years)
Diameter (times present value)
Sun’s fate
Orbits of:
Mars
Earth
Venus
Mercury
100
10
Helium
shell
flashes
Contraction
Leaves Main
sequence
Now
1
0
5
First
Red giant
peak
White
dwarf
10 12.1 12.2 12.3 12.3650 12.3655
Age (billions of years)
Death of a low mass star
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Red giant shrinks, becomes very hot
Expands to become a red giant again
Outer layers ejected into space.
Death of a low mass star
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Planetary
nebulae
are formed
Eventually
becomes a
white dwarf
On the HR diagrams, white
dwarf stars are
A.
B.
C.
D.
On the upper right
On the upper left
On the lower right
On the lower left
The Hertzsprung-Russell (HR)
Diagram
Absolute magnitude
-10
Main Sequence Stars
-5
Red
Giant
Stars
0
5
Sun
White
Dwarf
Stars
10
15
O
B
A
F
Spectral Class
Hot, not too bright
G
K
M
Higher mass stars
Fusion of
heavier elements
Contraction
(increasing temperature)
Cycle continues until core is made of Fe (iron)
Death of higher mass stars
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Explodes in a type II supernova
Then becomes
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a neutron star
or a black hole
Supernova 1987A (Type II)
Gas from the explosion hitting cool ring of gas
1994
2003
NASA
Neutron stars
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Fe core collapses
Electrons enter nuclei, neutrons and
neutrinos formed
Carries energy outward, causing an
explosion
Neutron star or black hole?
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If very massive it becomes a black hole
Otherwise it the remaining core is
called a neutron star

If this spins, we call
it a pulsar
Jocelyn Bell Burnell discovered pulsars!
What’s a theory?
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Start with an hypothesis
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Must fit evidence
Testable
Falsifiable
Einstein’s theory of Relativity
Fits evidence?
Testable?
Falsifiable?
Relativity in a nutshell
Matter tells space-time how to curve
Space-time tells matter how to move
Evidence – time dilation
Sun
Earth
Viking Lander sent a signal to Earth
Space was stretched, so time was too!
Viking Lander
Evidence – GPS
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Many of us own
GPS receivers.
Uses time signals
from satellites
orbiting Earth.
Does not work
unless corrected
for relativity!
wikipedia; DoD
Evidence: Wobble of Mercury
Shown by Einstein
Cornell
Evidence: gravitational lensing
Demo: bending light
Evidence: gravitational lensing
Evidence: gravitational lensing
Demo: Lensing in water
When a star stops fusing
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If it has more than 25 X M sun
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No outward force can resist gravity
It will become a black hole
Nothing on the surface can escape
(including light)
What forces act between a black
hole and a nearby object?
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Gravity is the only force acting!!!!
Depends on:
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Mass of objects
Distance between them
If the sun turned into a black hole,
what would happen to the Earth?
Can you get sucked into a
black hole?
Escape velocity
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How fast does the shuttle have to go in
order to leave Earth’s surface?
7 miles every second! (25,000 mph)
The moon?
5320 mph
The Sun?
1.38 million mph
Escape velocity
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Depends on the gravity between you
and the object you want to escape!
For a black hole, the escape velocity
(inside the event horizon) is greater
than the speed of light!
Do Black Holes Really Suck?
event
horizon
Normal
Weird
Singularity
The center of a black hole is a sphere (so is the event horizon)
Field trip to a black hole!!
event
horizon
Normal
Weird
Singularity
Volunteers?
At the event horizon
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Time slows waaaaayyy down
Someone jumping in would die a nasty
death
Someone watching would see the
person freeze in time
Finding black holes
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How can we see something that emits no light?
Look for binary systems
Make sure candidate is not a neutron star!
Finding black holes
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Matter near the
black hole is
traveling close to
the speed of light
When it rubs
together, it gives
off x rays we can
see
NASA/CXC
Summary
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Relativity tells us space and time can
be stretched
Escape velocity, event horizon
Black holes can be found, but not
directly seen