astro 113 week7 - physics & astronomyphysics.gmu.edu/~pesce/astro113/astro_113_week7.pdf ·...

Astronomy 113Dr. Joseph E. Pesce, Ph.D.

© Dr. Joseph E. Pesce, Ph.D.

Stellar Deaths/Endpoints


Low Mass Stars³ Like the Sun (< 2 M )

² �Live� about 10 billion years (sun is middle aged)² Create elements through Carbon, Nitrogen, and Oxygen through fusion

³ Core uses up He, C & O left, reactions stop³ Core collapses, shells of He and H ignite³ Envelope expands (T down L up)³ Becomes an Asymptotic Giant Branch star (AGB), very bright and enormous³ Pulsations in core fusion rate (every ~300,000 years) blow away bloated

atmosphere³ Outer atmosphere cools, dust forms, shell of atmosphere ejected and hot core

exposed, ionizing gas, causing it to glow² A Planetary Nebula is formed

q Expands to low density in ~50,000 yrs

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Low Mass Stars

T

L * He Flash

Planetary Nebula

AGB

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H

C,O

He C,O

H He

He


Low Mass Stars

³ Matter is returned to ISM (it is enriched)

³ C-O core is never ignited, it�s a left-over ember (white dwarf)

²Degenerate electrons, the size of the Earth

²Just cools thermally

²Very high density

²White dwarfs can’t be more massive than 1.4 M = Chandrasekar Limit

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The Life Cycle of a Low-Mass Star(After 10 billion years)

²Expands into a Red Giant (radius to ~Earth’s orbit)

²Outer atmosphere blows off to become a Planetary nebula

²Burned out core left as a White dwarf

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The Evolution of a Low-Mass Star13-6


© 2007-2014 Joseph E. Pesce, Ph.D.

Red Giant

&Planetary Nebula

Not to scale= Earth�s orbit© Dr. Joseph E. Pesce, Ph.D.

High Mass Stars³5-50 times the mass of the sun

²Last about 1 million years (very short!)²Create elements through iron (fusion)²�Onion skin�²Expand into Red Supergiant²Explode as a supernova²Leave behind neutron stars or black holes

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High Mass Stars³ Mass high enough after He fusion finishes that compression

ignites:² Carbon (T = 600 million K)² Neon (T = 1.2 billion K)² Oxygen (T = 1.5 billion K)

³ Fuses all of these at ever-increasing rates

² For 25 M C - 600 yrsNe - 1 yrO - 6 monthsSi - 1 day (at 2.7 billion K)

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High Mass Stars³ Fusion in shells (onion skin) leads to High L and Large R³ Supergiants (radius is out to orbit of ~Mars)³ Fuses through IRON, but iron in core is a problem

² Because iron requires more energy to fuse than it produces

³ Fusion in core stops, core collapses³ At first, degeneracy holds, but then it exceeds Chandrasekar limit (from

shell-fusion ash)

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Core - Fe

Outer Atmosphere - Hydrogen

Ca

Si

…

Ar

Ne

C

He

Onion-skin nature of High Mass Stars

Not to scale© Dr. Joseph E. Pesce, Ph.D.

Type II Supernova³ Core collapses catastrophically

² 1/10 sec, T~5 billion K² g-rays tear apart iron atoms² Neutrinos formed but can’t escape tremendous pressures² Material falling into core bounces back out, burning and blasting everything in it’s way² Extremely high T and densities in the shock wave² Outer atmosphere blasted, fused, neutrons create elements heavier than iron² Radioactive decay creates other elements² Extremely bright (outshining all other stars in galaxy briefly (200 billion)

³ TYPE II supernova

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Type I Supernova³ Begins as white dwarf³ If in binary, mass transfer can take place (see binaries above)³ White dwarf mass exceeds Chandrasekar limit and it explodes

³ TYPE I supernova

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Nova³Non-disruptive explosions of material

falling onto a White Dwarf from the accretion disk

³Object brightens for a short time, then fades

³Periodic



•

Inside the Supernova - 1a Massive

Outer Atmosphere

Time = 0 sec

Orbit of Mars

Not to Scale

•

Core -the size of Earth



Core -the size of Earth

Inside the Supernova - 1b Massive

Outer Atmosphere

Time = 0 sec

Not to Scale© Dr. Joseph E. Pesce, Ph.D.


Inside the Supernova - 2 Massive

Outer Atmosphere

Time = T+1/4 sec

Not to Scale

Core collapses

Neutron Star forms - 10km;or Black hole!

Matter falls in at near light speed



Inside the Supernova - 3

Time = T+1 sec

Not to Scale

Matter falls in at near light speed

Collapsing material hits central object and bounces

Neutron Star forms - 10km;Or Blackhole!

Massive quantities of neutrinos form - try to escape but can’t !!!!

High Temperature and Pressure lead to extreme fusion, massive quantities of protons, neutrons, & gamma-rays


Inside the Supernova - 4 Massive

Outer Atmosphere

Time = T+10 sec

Not to Scale

Blast wave, propelled by neutrinos and gamma-rays, fuses material as it goes



Inside the Supernova - 5

Time = T+10 min

Not to Scale

Blast wave continues to destroy stellar atmosphere

Neutrinos and gamma-rays finally fly free



The Aftermath - 6 Time = T+1 hour

Not to Scale

Supernova remnant

A chaotic, hot environment full of extremely high speed neutrons, protons, and electrons, gamma/X-rays, leading to the formation of elements heavier than Iron by neutron bombardment and radioactive decay.

The remnant continues to expand and dissipate over the next 10s of thousand years, adding material for the next generation stars.

The central object--blackhole or neutron star--heats the remnant and eventually is all that remains of the once-mighty star.



Supernova: The Animation

Time = 0 secTime = T+1/4 secTime = T+1 secTime = T+10 secTime = T+10minTime = T > 1 hourTime = T+1-10,000 yearsTime = T > 10,000 years

Black hole or neutron star remains


End States of Supernovae: Pulsars³ Collapsed core of high mass

star/supernova³ 10km diameter, extremely high

density³ Some are highly magnetized³ All spin rapidly³ Beam of particles squirted from

Magnetic axes• If toward us, see regular pulses• Can be 100s of pulses per second

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View From Earth:Rotation axis Magnetic Poles

To Earth


Pulsars in radio:

89.3ms= 11/sec

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Vela: 89ms (11x / sec)

Crab: (30x/sec)Youngest

B1937+21: (642x/sec) ; rotating 14% c !2nd fastest

B0329+54: 0.714519s (1.4 rot/sec)



13-37Endstates of Supernovae: Blackholes


Blackholes³3 times mass of the sun to billions of times³Small ones among stars in galaxies³Large ones, apparently at center of every

galaxy³Matter falling in heats up and we see it³Consumes locally, but has effect on larger

scales (jets)³What goes in can’t come out³Don’t know anything about interior (physics

doesn’t �work�)

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Evolution of High-Mass Stars13-39


Importance of High Mass Stars

³Create all elements though Fe internally³Create all heavier elements in explosion³Explode and disperse elements to next

generation stars³Stimulate star formation³We wouldn’t be here but for high mass

stars!!

We ARE star stuff!!

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Thank You!


astro 113 week7 - physics & astronomyphysics.gmu.edu/~pesce/astro113/astro_113_week7.pdf ·...

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