Slide 1

Stellar EvolutionStellar Evolution

M<0.08 .08<M<0.4 0.4<M<1.4 1.4<M<~4 M>~4

P R O T O S T A R M a i n S e q u e n c e

D G I A N T

Planetary Supernova Nebula

W h i t e D w a r f

B r o w n D w a r f Neutron Star OR

Black Hole

M A I N S E Q U E N C ER E D G I A N T

W H I T E D W A R F

B R O W N D W A R F

M is mass of the star in units of mass of the Sun M

Slide 2

Protostar

• Gravitational contraction of space matter.

• Source of energy is gravity.

• Starts typically with a size of several light years. (1 ly ~ 1013 km.)

• Many gravitational contraction points

• When protostar core gets hot enough to start nuclear fusion, a normal star is born.

Slide 3

Main Sequence Stars

• Source of energy is nuclear fusion

• 4 H He + energy as helium mass is less than 4H by 0.7%.

• Star very stable with gravity pulling in and heat energy pushing out.

• The more massive the star, the faster it uses hydrogen.

Slide 4

Red Giant Stars

• After core hydrogen is depleted, core contracts, heats up more and when temperature reaches 100,000,000ºK, 3He C + energy fusion starts.

• Outside of the core the temperature is now over 1,000,000ºK and there is plenty of hydrogen and 4HHe + energy production starts.

• Now more energy is produced, so star expands to about 100 times original size.

• Sun will become a red giant in about 5 billion years, swell about 100 times in diameter and absorb Mercury, Venus and Earth.

Slide 5

Red Giant stars

Slide 6 Fig. 13-8a, p.265

Betelgeuse in Orion

Slide 7 Fig. 13-8b, p.265

Betelgeuse

Slide 8

Death of Stars

• Depends on mass.

• For stars < 4M after all nuclear fusion has stopped, the star collapses into white dwarf, the size of Earth.

• If mass > 1.4 M during collapse the outer layers are expelled and become planetary nebula (nothing to do with planets).

Slide 9 p.260

Ring Nebula in Lyra

Slide 10 Fig. 13-1, p.261

Helix planetary nebula

Knots areabout 100 AUtails 1,000 AU

Slide 11 Fig. 13-3, p.262

Dumbbellplanetarynebula

Slide 12

Egg nebulaplanetary nebula

Slide 13 Fig. 13-5, p.263

Slide 14 Fig. 13-6a, p.264

Sirius B is a white dwarf

Slide 15

Supernova

• For Red Giants with mass > 4 M becomes iron. Iron cannot fuse to higher mass elements and fusion stops and star starts collapsing.

• During the collapse all the outer layers become extremely hot and nuclear fusion starts everywhere except in the core.

• The star explodes into a supernova and the core squeezes into a neutron star or black hole.

• During supernova the star brightens 1010 to 1011 times. Often outshines the whole galaxy.

Slide 16

AST1605.swf

Slide 17

AST1608.swf

Slide 18

Supernova

Supernova

Slide 19 Fig. 13-13, p.268

Tarantula Nebula in Large Magellanic Cloud (a neighboring galaxy)and 1987A supernova

Before and after February 24, 1987

Slide 20

Supernova• Rise in brightness very rapid ~ 1 day.• Drop in intensity ~ 1 year.• On the average 2 supernova per century per galaxy.• Last supernova observes in our galaxy was about 400

years ago.• Last supernova observed in “naked eye” was in 1987

in Large Magellanic Cloud galaxy.• Many supernovae are observed each year in far away

galaxies.

Slide 21

AST1609.swf

Slide 22 Fig. 13-9, p.266

Slide 23

Supernova remnants

• 80% to 90% of the star blows out.• Core squeezes into a neutron star or black

hole.• Neutron star is the size of a city, spins very

rapidly and emits pulses that gave the original name of pulsars.

• If the mass of neutron star is too large, it becomes a black hole.

Slide 24 Fig. 13-11a, p.267

Crab nebularemnant ofSupernova 1054.Has a pulsarin it.

Slide 25 Fig. 13-11b, p.267

Veil nebulasupernovaexploded20,000 yearsago

Slide 26 Fig. 13-12a, p.267

Tycho’sSupernovaexpandingsince 1604

Slide 27 Fig. 13-12b, p.267

Cassiopeia supernova remnant

Slide 28 Fig. 13-18, p.271

Size ofneutronstar

Slide 29 Fig. 13-20a, p.272

Slide 30 Fig. 13-21, p.272

Location of pulsars (neutron stars)

Slide 31 Fig. 13-22, p.273

Slide 32 Fig. 13-23, p.274

CrabNebula Pulsarin Xrayat maximumand minimum

Slide 33 Fig. 13-26, p.275

Binary pulsarperihelionshift due togravity wavesas predictedby Einsteingeneral theoryof gravity

4º per year.

Slide 34

LIGO Gravitational Wave detection facility

Slide 35

LIGO Facility

Slide 36

LIGO Interferometer where mirrors are located