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Agenda
Types of star deaths Relativity Black holes Evidence for both
Start registering your clickers. There’s a link from webct.
He core contracting
H fusing
Exterior expanding
H runs out: star becomes a red giant
Mass alone determines death
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?
Sun’s fateD
iam
ete
r (t
ime
s p
rese
nt v
alu
e)
1
100
10
Age (billions of years)
0 5 10 12.1 12.2 12.3 12.3650 12.3655
Contraction
FirstRed giant
peakNow
Leaves Mainsequence
White dwarf
Orbits of:MarsEarth
VenusMercury
Helium shell
flashes
Sun’s fateD
iam
ete
r (t
ime
s p
rese
nt v
alu
e)
1
100
10
Age (billions of years)
0 5 10 12.1 12.2 12.3 12.3650 12.3655
Contraction
FirstRed giant
peakNow
Leaves Mainsequence
White dwarf
Orbits of:MarsEarth
VenusMercury
Helium shell
flashes
Sun’s fateD
iam
ete
r (t
ime
s p
rese
nt v
alu
e)
1
100
10
Age (billions of years)
0 5 10 12.1 12.2 12.3 12.3650 12.3655
Contraction
FirstRed giant
peakNow
Leaves Mainsequence
White dwarf
Orbits of:MarsEarth
VenusMercury
Helium shell
flashes
Death of a low mass star
Red giant shrinks, becomes very hot Expands to become a red giant again Outer layers ejected into space.
Death of a low mass star
Planetary
nebulae
are formed Eventually
becomes a
white dwarf
On the HR diagrams, white dwarf stars are
A. On the upper right
B. On the upper left
C. On the lower right
D. On the lower left
The Hertzsprung-Russell (HR) Diagram
O B A F G K M
15
5
10
-10
0
-5
Spectral Class
Sun
Main Sequence Stars
White Dwarf Stars
Red Giant Stars
Hot, not too bright
Abs
olut
e m
agni
tude
Higher mass stars
Fusion ofheavier elements
Contraction (increasing temperature)
Cycle continues until core is made of Fe (iron)
Death of higher mass stars
Explodes in a type II supernova Then becomes
a neutron star or a black hole
Supernova 1987A (Type II)
1994 2003
Gas from the explosion hitting cool ring of gas
NASA
Neutron stars
Fe core collapses Electrons enter nuclei, neutrons and
neutrinos formed Carries energy outward, causing an
explosion
Neutron star or black hole?
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?
Start with an hypothesis Must fit evidence Testable Falsifiable
Einstein’s theory of Relativity
Fits evidence?
Testable?
Falsifiable?
Matter tells space-time how to curve
Relativity in a nutshell
Space-time tells matter how to move
Evidence – time dilation
Viking Lander sent a signal to EarthSpace was stretched, so time was too!
Earth
Viking Lander
Sun
Evidence – GPS
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
Cornell
Shown by Einstein
Evidence: gravitational lensing
Demo: bending light
Evidence: gravitational lensing
Evidence: gravitational lensing
Demo: Lensing in water
When a star stops fusing
If it has more than 25 X M sun
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?
Gravity is the only force acting!!!! Depends on:
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
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
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
Time slows waaaaayyy down Someone jumping in would die a nasty
death Someone watching would see the
person freeze in time
Finding black holes
How can we see something that emits no light? Look for binary systems Make sure candidate is not a neutron star!
Finding black holes
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
Relativity tells us space and time can be stretched
Escape velocity, event horizon Black holes can be found, but not
directly seen