Chapters 12 Chapters 12 and 13: and 13: The Lives and Deaths of Stars - Stellar Evolution

NGC 2264

WHAT DO YOU THINK?WHAT DO YOU THINK? How do stars form?How do stars form? Are stars still forming today?Are stars still forming today? Do more massive stars shine longer?Do more massive stars shine longer?Will the Sun someday stop shining? If

so, how?Where do heavy elements on the Earth

like carbon, silicon, oxygen, iron, and uranium come from?

What is a pulsar?

You will discover…You will discover…The remarkable transformations of older The remarkable transformations of older

stars into giants and supergiants.stars into giants and supergiants.That some dying stars eject material that That some dying stars eject material that

creates new generations of stars, while creates new generations of stars, while others act as beacons that enable others act as beacons that enable astronomers to pinpoint distant galaxies.astronomers to pinpoint distant galaxies.

You will discover…You will discover…What happens when stars “run out of fuel.”How heavy elements are created.What happens at the end of stellar

evolution.Why some stars go out relatively gently,

while others go with a bang.The incredible densities of neutron stars

and how they are observed.

Star FormationStar Formation

Stars form Stars form from the from the mutual mutual gravitational gravitational attraction attraction between gas between gas and dust and dust inside giant inside giant molecular molecular clouds.clouds.

HR Diagram HR Diagram (Main Sequence (Main Sequence = the red line).= the red line).Main Sequence Main Sequence Star definition:Star definition:1. Star is fusing 1. Star is fusing

Hydrogen to Hydrogen to Helium in its Helium in its

core.core.2. Star is not 2. Star is not expanding or expanding or contracting.contracting.

If a star is If a star is above or below above or below

the Main the Main Sequence, then Sequence, then something else something else

is going on. is going on. We need to find We need to find out what that is.out what that is.

What if our Sun were 1.5 times as big as it is?

What if the Sun were 3 times bigger?

106 years = 1 million years

Summary of Stellar EvolutionSummary of Stellar Evolution

The evolution of stars depends on their masses.The evolution of stars depends on their masses. We will look at three sizes of stars:We will look at three sizes of stars:

Stars like our Sun.Stars like our Sun. Big stars (8-25 times the Sun’s mass).Big stars (8-25 times the Sun’s mass). Huge stars (more than 25 times the Sun’s mass).Huge stars (more than 25 times the Sun’s mass).

Stars like our Sun (MStars like our Sun (MOO = 1) will turn into = 1) will turn into Planetary Nebulae and White Dwarf Stars, then Planetary Nebulae and White Dwarf Stars, then end up as Black Dwarfs that give off no light.end up as Black Dwarfs that give off no light.

Big stars (8-25 MBig stars (8-25 MOO) will end up as Neutron Stars.) will end up as Neutron Stars. Huge stars (>25 MHuge stars (>25 MOO) will end up as Black Holes.) will end up as Black Holes.

Summary of Stellar EvolutionSummary of Stellar Evolution

The evolution of stars depends on their masses.

Stars Like Our Sun (MStars Like Our Sun (MOO = 1) = 1)

Main SequenceMain SequenceRed GiantRed GiantRed SupergiantRed SupergiantPlanetary Nebula and White DwarfPlanetary Nebula and White DwarfBlack DwarfBlack Dwarf

The Sun “burns” hydrogen now. In about 5 billion years, it The Sun “burns” hydrogen now. In about 5 billion years, it will almost run out of hydrogen, and turn into a Red Giant.will almost run out of hydrogen, and turn into a Red Giant.

The Sun Today andThe Sun Today andas a Red Giantas a Red Giant

Red Giant Stars in a Star ClusterRed Giant Stars in a Star Cluster

Life History of Stars Like Our SunLife History of Stars Like Our Sun

1. Main Sequence2. Red Giant3. Red Supergiant4. Planetary Nebula and White Dwarf5. Black Dwarf

Our Sun in Old Age –Our Sun in Old Age –a Red Supergianta Red Supergiant

Near the end of its life, the Sun will become a Supergiant.

From Supergiant to White DwarfFrom Supergiant to White Dwarf

Our Sun will “puff off” its outer layers to form a Planetary Nebula, and the Sun’s remaining core material will become a White Dwarf star.

It might look like this (Helix Nebula)It might look like this (Helix Nebula)

More Planetary NebulaeMore Planetary Nebulae

Sirius’s White Dwarf FriendSirius’s White Dwarf Friend

Sirius B, a white dwarf, at the five o’clock position

Both emit X-rays

Big Stars and Huge StarsBig Stars and Huge Stars(8-25 M(8-25 MOO) (>25 M) (>25 MOO))

Main SequenceMain SequenceBright SupergiantBright SupergiantSupernova ExplosionSupernova ExplosionBig Star Big Star →→ Neutron Star Neutron StarHuge Star Huge Star →→ Black Hole Black Hole

Structure of Big and Huge Stars in Old Age –Structure of Big and Huge Stars in Old Age –a Bright Supergianta Bright Supergiant

The old star’s core is now made of Iron. Oops!

Disaster is not far away.Disaster is not far away.

The Supergiant’s core is made of Iron, The Supergiant’s core is made of Iron, which cannot be “burned” to make any which cannot be “burned” to make any heavier elements.heavier elements.

So the star’s core collapses because of So the star’s core collapses because of gravity, then rebounds, and the star gravity, then rebounds, and the star explodes.explodes.

We have a Supernova Explosion.We have a Supernova Explosion.

HOW FAST DOES ALL THIS HAPPEN?

Supernovae Make a MessSupernovae Make a Mess

Computer simulations showing how chaotic the supernova is deep inside the star as it begins to explode.

A Supernova RemnantA Supernova Remnant

X-ray image of the Cygnus Loop

HST image of the Cygnus Loop

Gum NebulaGum Nebula

The Gum Nebula, created by a supernova 11,000 years ago, is the largest known supernova remnant. It now has a diameter of about 2,300 ly.

Supernova 1987A (LMC)Supernova 1987A (LMC)

Big and Huge Stars – Big and Huge Stars – the Final Stagethe Final Stage

Neutron Stars result from Supernova Neutron Stars result from Supernova Explosions of Big Stars.Explosions of Big Stars.

Black Holes result from Supernova Black Holes result from Supernova Explosions of Huge Stars.Explosions of Huge Stars.

Neutron Star’s InteriorNeutron Star’s Interior

The neutron star has a superconducting, superfluid core 9.7 km in radius, surrounded by a 0.6-km-thick mantle of superfluid neutrons. The neutron star’s crust is only 0.3 km thick.

Neutron StarsNeutron StarsHow Big? How Dense?How Big? How Dense?

A typical Neutron Star would fit between A typical Neutron Star would fit between Loyola Academy and Chicago’s Loop.Loyola Academy and Chicago’s Loop.

One teaspoonful of Neutron Star material One teaspoonful of Neutron Star material would weigh one billion tons on Earth.would weigh one billion tons on Earth.

A Pulsar is a Rotating, Magnetized Neutron StarA Pulsar is a Rotating, Magnetized Neutron Star

Charged particles are accelerated near a neutron star’s magnetic poles and produce two beams of radiation. These beams act like the light from a lighthouse when seen from Earth.

Radio Signals or X-raysRadio Signals or X-raysfrom a Pulsarfrom a Pulsar

Crab Nebula and PulsarCrab Nebula and Pulsar

The Crab’s visible flashes and X-ray pulses have identical periods of 0.033 seconds.

Colliding Neutron StarsColliding Neutron Stars

Collisions of Neutron Stars may cause Collisions of Neutron Stars may cause creation of elements heavier than Iron, creation of elements heavier than Iron, such as Gold, Silver, Platinum, Uranium.such as Gold, Silver, Platinum, Uranium.

You can thank the stars for your jewelry, as You can thank the stars for your jewelry, as well as for the elements you are made of well as for the elements you are made of (Carbon, Oxygen, Phosphorus, Nitrogen, (Carbon, Oxygen, Phosphorus, Nitrogen, Iron, etc.). They made it all from Hydrogen.Iron, etc.). They made it all from Hydrogen.

Black HoleBlack Hole

Summary of Stellar EvolutionSummary of Stellar Evolution

The evolution of stars depends on their masses.

Summary of Stellar EvolutionSummary of Stellar Evolution The evolution of stars depends on their masses.The evolution of stars depends on their masses. Stars like our Sun (MStars like our Sun (MOO = 1) will turn into = 1) will turn into

Planetary Nebulae and White Dwarf Stars, then Planetary Nebulae and White Dwarf Stars, then end up as Black Dwarfs that give off no light.end up as Black Dwarfs that give off no light.

Big stars (8-25 MBig stars (8-25 MOO) will end up as Neutron Stars, ) will end up as Neutron Stars, after a Supernova Explosion.after a Supernova Explosion.

Huge stars (>25 MHuge stars (>25 MOO) will end up as Black Holes, ) will end up as Black Holes, after a Supernova Explosion.after a Supernova Explosion.

Material from old stars (Planetary Nebulae, Material from old stars (Planetary Nebulae, Supernova Remnants, etc.) gets recycled to Supernova Remnants, etc.) gets recycled to form new stars.form new stars.

Stars – The Ultimate RecyclersStars – The Ultimate Recyclers

Material from old stars (Planetary Nebulae, Supernova Material from old stars (Planetary Nebulae, Supernova Remnants, etc.) gets recycled to form new stars. Remnants, etc.) gets recycled to form new stars.

WHAT DID YOU THINK?WHAT DID YOU THINK? How do stars form? How do stars form? Stars form from the mutual gravitational attraction Stars form from the mutual gravitational attraction

between gas and dust inside giant molecular clouds.between gas and dust inside giant molecular clouds. Are stars forming today? Are stars forming today? Yes. Astronomers have seen stars that have just arrived Yes. Astronomers have seen stars that have just arrived

on the main sequence, as well as infrared images of gas on the main sequence, as well as infrared images of gas and dust clouds in the process of forming stars.and dust clouds in the process of forming stars.

Do stars with greater mass shine longer? Do stars with greater mass shine longer? No. No. LowerLower-mass stars last longer because the lower -mass stars last longer because the lower

gravitational force inside them causes fusion to take gravitational force inside them causes fusion to take place at slower rates compared to the fusion inside place at slower rates compared to the fusion inside higher-mass stars.higher-mass stars.

WHAT DID YOU THINK?WHAT DID YOU THINK? Will the Sun someday cease to exist? If so, how? The Sun will shed matter as a planetary nebula in about 6 billion

years and then cease nuclear fusion. Its remnant white dwarf will dim over the succeeding billions of years.

What are the origins of the carbon, silicon, oxygen, iron, uranium, and other heavy elements on Earth?

These elements are created during stellar evolution, by supernovae, and by colliding neutron stars.

What is a pulsar? A pulsar is a rotating neutron star in which the magnetic field’s

axis does not coincide with the rotation axis. The beam of radiation it emits sweeps across our region of space, like the light from a lighthouse.

STELLAR EVOLUTION (star types are underlined)STELLAR EVOLUTION (star types are underlined)1. OUR SUN1. OUR SUN

Object (and transition)Object (and transition) What's HappeningWhat's Happening Other StuffOther Stuff

OUR SUNOUR SUN Hydrogen core fusionHydrogen core fusion lifetime = 10 Billion yearslifetime = 10 Billion years↓↓ (makes Helium core)(makes Helium core)RED GIANTRED GIANT Hydrogen shell fusionHydrogen shell fusion size = out to Venus, toasts size = out to Venus, toasts

EarthEarth↓↓ (Helium core flash)(Helium core flash)shrinksshrinks Helium core fusionHelium core fusion↓↓ (makes Carbon & Oxygen core)(makes Carbon & Oxygen core)RED SUPERGIANTRED SUPERGIANT Helium shell fusionHelium shell fusion size = out to Earth's orbitsize = out to Earth's orbit↓↓ (Helium shell flash)(Helium shell flash)PLANETARYPLANETARY made of dust & gasmade of dust & gas star's outer layers "puff off”star's outer layers "puff off”NEBULANEBULAandandWHITE DWARFWHITE DWARF made of Carbon & Oxygenmade of Carbon & Oxygen size = the Earthsize = the Earth↓↓ (cools off)(cools off)BLACK DWARFBLACK DWARF gives off no lightgives off no light

2. BIG STARS (8-25 times Sun's mass) and HUGE STARS (more than 25 2. BIG STARS (8-25 times Sun's mass) and HUGE STARS (more than 25 times Sun's mass)times Sun's mass)

ObjectObject What's Happening and Other StuffWhat's Happening and Other Stuff

BIG STARSBIG STARS lifetime = 15 Million yearslifetime = 15 Million yearsandandHUGE STARSHUGE STARS lifetime = 3 Million yearslifetime = 3 Million years↓↓ (fusion of Hydrogen, Helium, Carbon, and Oxygen - makes Iron core)(fusion of Hydrogen, Helium, Carbon, and Oxygen - makes Iron core)BRIGHT SUPERGIANTSBRIGHT SUPERGIANTS size = out to Jupiter's orbit or biggersize = out to Jupiter's orbit or bigger↓↓SUPERNOVA EXPLOSIONSUPERNOVA EXPLOSION star collapses, rebounds, explodesstar collapses, rebounds, explodes↓↓BIG STARSBIG STARSend up asend up asNEUTRON STARSNEUTRON STARS made of Neutrons & other stuff, size = Chicagomade of Neutrons & other stuff, size = Chicago

HUGE STARSHUGE STARSend up asend up asBLACK HOLESBLACK HOLES gravity is so strong that light cannot escapegravity is so strong that light cannot escape