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Incredible Shrinking StarsPowerPoint Presentation

Incredible Shrinking Stars

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Incredible Shrinking Stars. The End States of Stars. White Dwarfs. Earth. White Dwarf. White Dwarf Facts. * Composition: carbon, oxygen * Mass limit < 1.4 M ( Chandrasekhar Limit ) * Avg mass 0.5 M . Mass, radii density 1 ton/cm 3. Sirius B (white dwarf). Sirius.

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White Dwarf

White Dwarf Facts

* Composition: carbon, oxygen

* Mass limit < 1.4 M (Chandrasekhar Limit)

* Avg mass 0.5 M

Mass, radii density 1 ton/cm3

Neutron Star: Final state of stellar core in some

supernova explosions.

- Composition: neutrons
- Mass: 1 – 2 M

Density ~ 108 ton/cm3

1. Your weight is enormous

m = your mass

M = neutron star mass

R = neutrons star radius

150 lbs on Earth ~ 1013 lbs on a neutron star

Splat!

2. Marshmallows become dangerously explosive

Energy released equivalent to

detonating ~ 10 tons of TNT.

Drop marshmallow on

neutron star.

* Neutron stars should be rapidly spinning . . .

Neutron Star

(small diameter,

rapid spin)

Core, before collapse

(large diameter, slow spin)

Fast

* Neutron stars should have strong magnetic fields . . .

Field lines become concentrated.

- Conversion of energy of rotation into
- em radiation

* Rotating magnetic

field creates electric

field.

* Electric field drives

electrons along lines

of magnetic field.

* Electrons radiate –

mainly where magnetic field strong.

* White Dwarf: M 1.4 M

* Neutron Star: M 2 - 3 M

If stellar core should become iron with

mass 2 - 3 M . . .

Black Hole results!

Space is curved – Gravity is a result of geometry!

[2-dimensional analog]

Gravity causes time to slow down . . .

Observes

ground-floor

clock to be

slow.

Photon loses energy

as it moves upward –

gravitational redshift.

Bottom of tower

- e.g.,
- 2 cycles/sec
- (a) 1 cycle/sec

- more ticks of clock
- (a) fewer ticks of clock

Black hole: infinitely deep ‘puncture’ in space-time.

infinite density!

Schwarzchild Radius (RS)

Event Horizon

Schwarzchild Black Hole

At RS, escape velocity =

speed of light

RS (km) = 3M M = mass in units of Sun’s mass

e.g., M = 1 M RS = 3 1 = 3 km

6 km

The Sun as a black hole

B. H.

Falling into a Black Hole

1. Stretching

Less gravity

2. Squeezing

More gravity

Result: Heating

* By their effects on other objects.

- Strong x-ray source
- Only one star detected
- Motion of that star unseen star is very
- massive

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