Agenda

Types of star deaths Relativity Black holes Evidence for both

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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

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ete

r (t

ime

s p

rese

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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