Stellar End-States… Stellar End-States… J. B. S. Haldane (1892 – 1964) from Possible Worlds, Now, my suspicion is that the Universe is not only queerer than we suppose, but queerer than we can suppose.
Stellar End-States… J. B. S. Haldane (1892 – 1964) from Possible Worlds, 1927 Now, my suspicion is that the Universe is not only queerer than we suppose,
Jan 16, 2016
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Stellar End-States…Stellar End-States…
J. B. S. Haldane (1892 – 1964)from Possible Worlds, 1927
Now, my suspicion is that the Universe is not only queerer than we suppose, but queerer than we can suppose.
WHAT DO YOU THINK?
1. Will the Sun someday cease to shine brightly?
2. What is a nova? What is a supernova?
3. Where does carbon, silicon, oxygen, iron, uranium, & other heavy elements come from?
4. What is a pulsar?
Essay Questions for the exam…Essay Questions for the exam…
How will our Sun evolve as a star? What will its final state be? Compare its predicted evolution to that of higher-mass stars. How do they end? How do we know?
Essay Questions for the exam…Essay Questions for the exam… (a) What is a pulsar? Where does it get its energy? How do we know? (b) Describe a black hole. How do astronomers detect them if they give off no light?
The Evolution of 1MThe Evolution of 1Moo Star Star
90% of Life as “Main 90% of Life as “Main Sequence” starSequence” star
Fuses Hydrogen to HeliumFuses Hydrogen to Helium
The Evolution of 1MThe Evolution of 1Moo Star Star
90% of Life as “Main 90% of Life as “Main Sequence” starSequence” star
Fuses Hydrogen to HeliumFuses Hydrogen to Helium
He collects in core & builds He collects in core & builds up over timeup over time
The Evolution of 1MThe Evolution of 1Moo Star Star
He core collapses, triggers expansion to He core collapses, triggers expansion to Red GiantRed Giant
Fuses H to He in shellFuses H to He in shell
Eventually fuses He to Carbon in CoreEventually fuses He to Carbon in Core
Creates dust grains in outer edgesCreates dust grains in outer edges
Stellar Model of a Sun-Like StarStellar Model of a Sun-Like Star
A red giant!
The Evolution of 1MThe Evolution of 1Moo Star Star
Not large enough to fuse Carbon to Not large enough to fuse Carbon to heavier elements!heavier elements!Central core eventually collapsesCentral core eventually collapsesOuter layers Outer layers graduallygradually “blow” off “blow” off
Forms a Forms a planetary nebula planetary nebula “death shroud”“death shroud”
Core collapseCore collapse finally stops as finally stops as white dwarfwhite dwarf
Planetary Nebulae
“Death Shrouds” of ejected gas surrounding
collapsed white dwarf corpse
(Not “planets”!)
Planetary Nebulae
“Death Shrouds” of ejected gas surrounding
collapsed white dwarf corpse
(Not planets!)
Model of Planetary Nebula seen almost edge-on
The Evolution of 1MThe Evolution of 1Moo Star Star
Forms a Forms a planetary nebula planetary nebula “death shroud”“death shroud”
Core collapseCore collapse finally stops as finally stops as white dwarfwhite dwarf
Stellar “corpse” is stable, tiny, hot…...Stellar “corpse” is stable, tiny, hot…...
Supported by electron degeneracy pressure
Sirius & White Dwarf
Sirius & White Dwarf
In X- Rays
Note better Resolution!
Forming as a protostar!: Forming as a protostar!: Thermal pressure < gravity! (collapsing!)Thermal pressure < gravity! (collapsing!)Pressure depends on temperaturePressure depends on temperature
Fusing H to He as “main-sequence” starFusing H to He as “main-sequence” star::Radiation/Gas pressures = gravity (stable!)Radiation/Gas pressures = gravity (stable!)Pressure depends on temperaturePressure depends on temperature
What supports What supports weightweight of 1M of 1Moo star? star?
After Red Giant stage?After Red Giant stage?
No longer fusing!
Electrons to the rescue!Electrons to the rescue!
Degeneracy Pressure Degeneracy Pressure ((Pressure no longer depends on temperature)Pressure no longer depends on temperature)
What supports What supports weightweight of 1M of 1Moo star? star?
Degeneracy PressureDegeneracy Pressure• ““Two particles cannot occupy same space with Two particles cannot occupy same space with
same momentum (energy)”same momentum (energy)”
• For For veryvery dense solids, electrons dense solids, electrons cannotcannot all be in all be in ground statesground states
• Electrons become VERY energetic--- velocities Electrons become VERY energetic--- velocities approach speed of light.approach speed of light.
• Pressure holding up star no longer depends on temperature.
White DwarfsWhite Dwarfs
Stable! Stable! GravitationalGravitational pressure in = pressure in = electron degeneracy electron degeneracy pressure outpressure out
Not fusing: Not fusing: Generates no Generates no new new energyenergy
Cooling off: Cooling off: Radiates heat into space, getting fainter over time
White DwarfsWhite Dwarfs
Very dense; 0.5 - 1.4 MVery dense; 0.5 - 1.4 M packed into a packed into a sphere the size of the Earth!sphere the size of the Earth!
White DwarfsWhite Dwarfs
• Degenerate matter obeys different laws of physics. Degenerate matter obeys different laws of physics. • More massive star => More massive star => smallersmaller core becomes! core becomes!
• increased gravity makes star denserincreased gravity makes star denser• greater density increases degeneracy pressure to greater density increases degeneracy pressure to
balance gravitybalance gravity
Limit on White Dwarf MassLimit on White Dwarf Mass
Predicted gravity will Predicted gravity will overcome electron overcome electron degeneracy degeneracy pressure if white pressure if white dwarf mass greater dwarf mass greater than 1.4 Mthan 1.4 M
Subrahmanyan Chandrasekhar(1910-1995)
Chandrasekhar Limit
Subrahmanyan ChandrasekharSubrahmanyan Chandrasekhar
Indeed, I would feel that an appreciation of the arts in a conscious, disciplined way might help one to do science better.
What if end-state core is larger?What if end-state core is larger?
Degeneracy applies to nuclear particles, too!Degeneracy applies to nuclear particles, too!
Collapses until Collapses until neutron degeneracy neutron degeneracy pressure pressure holds up the corpse (holds up the corpse (neutron star)
If even neutron degeneracy can’t support the weight of the core…
Black Hole!
Nova!Nova!
Peak Brightness 2 months later
50,000 times dimmer!
Nova!Nova!
If white dwarf is part of a If white dwarf is part of a close binaryclose binary:: Its gravity can pull matter from nearby starIts gravity can pull matter from nearby starForms an Forms an accretion diskaccretion disk around White dwarf around White dwarfFriction heats itFriction heats it If matter falls onto WD, eventually H fusion can begin…If matter falls onto WD, eventually H fusion can begin…
White Dwarf White Dwarf suddenly, temporarily suddenly, temporarily gets much gets much brighter….brighter….
Recurrent NovaeRecurrent Novae
Even Larger Stars –Ferraris!Even Larger Stars –Ferraris!
Stars 10x larger than our SunStars 10x larger than our SunFuse faster!Fuse faster!Shine brighter!!Shine brighter!!Live very short lives…Live very short lives…
But…But…
Make every element in your body after Make every element in your body after Helium!Helium!
Even Larger Stars –Ferraris!Even Larger Stars –Ferraris!
Evidence Supporting TheoriesEvidence Supporting Theories
Periodic Table AbundancesPeriodic Table AbundancesMultiples of “4” match Helium fusion chainMultiples of “4” match Helium fusion chain
Neutrinos from SupernovaNeutrinos from SupernovaSN 1987a caught “early” in explosionSN 1987a caught “early” in explosion
Cosmic Rays Cosmic Rays
The Periodic Table of Elements!The Periodic Table of Elements!
Periodic Table AbundancesPeriodic Table Abundances
Periodic Table AbundancesPeriodic Table Abundances
Atomic Masses
H = 1
He = 4
C = 12
O = 16
N = 20
Mg = 24
Si = 28
S = 32
Fe = 56
Supermassive stars lose
mass even before they
blow up!
SUPERNova!SUPERNova!
Neutron StarsNeutron Stars
• What is a neutron star?What is a neutron star? (THEORY) (THEORY)
• What is a pulsar?What is a pulsar? (OBSERVATION) (OBSERVATION)
• What What evidenceevidence do we have that they are do we have that they are one in the same?one in the same?
Neutron Star THEORYNeutron Star THEORY
• Leftover Leftover corescores from supernova explosions from supernova explosions
• Supported by Supported by neutron degeneracy pressureneutron degeneracy pressure
• Very Very TINYTINY 1.5 M1.5 M with a diameter of 10 to 20 kmwith a diameter of 10 to 20 km
Chandra X-ray image of the neutron star left behind by a supernova observed in A.D. 386.The remnant is known as G11.20.3.
Neutron Star THEORYNeutron Star THEORY
• Very Very DENSE:DENSE: (10 (101212 g/cm g/cm3 3 )) & & HOTHOT
• Very rapid Very rapid RotationRotation: Period = 0.03 to 4 sec: Period = 0.03 to 4 sec
• VERY strong VERY strong MagneticMagnetic fields: 10 fields: 101313 x Earth’s. x Earth’s.
Chandra X-ray image of the neutron star left behind by a supernova observed in A.D. 386.The remnant is known as G11.20.3.
Neutron Star THEORYNeutron Star THEORY
Discovery of 1Discovery of 1stst Pulsar Pulsar
In 1967, graduate student Jocelyn Bell and In 1967, graduate student Jocelyn Bell and her advisor Anthony Hewish accidentally her advisor Anthony Hewish accidentally discovered a radio source in discovered a radio source in VulpeculaVulpecula..
Sharp pulse recurred every 1.3 sec.Sharp pulse recurred every 1.3 sec. Determined it was 300 pc away.Determined it was 300 pc away. They called it a “They called it a “pulsar”pulsar”, but what was it?, but what was it?
The Crab PulsarThe Crab PulsarThe mystery was solved when a pulsar was discovered in the heart of the Crab Nebula.
The Crab pulsar also pulses in visual light.
Pulsar ObservationsPulsar Observations
Very tiny pulse “widthVery tiny pulse “width” ” Object must be extremely small.Object must be extremely small.Even white dwarf is too large!Even white dwarf is too large!
Very regular pulse of energyVery regular pulse of energy Occasional “Occasional “GlitchesGlitches” in signal” in signalA few seen in X-ray binary systemsA few seen in X-ray binary systems
High temperatures, large massesHigh temperatures, large masses
Pulsar ObservationsPulsar Observations
Synchotron emissionSynchotron emission --- non-thermal --- non-thermal process where radiation is process where radiation is emittedemitted by by charged particles moving close to the charged particles moving close to the speed of light around magnetic fields.speed of light around magnetic fields.
Slow downSlow down over time over timeFastest signalFastest signal oscillation in oscillation in
Supernova RemnantsSupernova Remnants
Neutron Star = Pulsar!!Neutron Star = Pulsar!!Theory Observation
1. Tiny Small Pulse Width
2. Rotating Fast Regular Pulse up to
1000 times a second
3. Strong Magnetic Field Synchrotron Radiation
4. Dense, Massive X-ray Binary accretiondisks surround pulsar
5. Supernova Corpse See in SN Remnants
6. Energy From Rotation Slow Down over time
Model of Pulsar as Rotating Neutron Star
““Lighthouse” Model of PulsarLighthouse” Model of Pulsar
Pulsars are the lighthouses of Galaxy!
Pulsars as Celestial BeaconsPulsars as Celestial Beacons
Pulsars vs. Neutron Stars?Pulsars vs. Neutron Stars?All pulsars are neutron stars, but all All pulsars are neutron stars, but all
neutron stars are neutron stars are notnot pulsars!! pulsars!!
Whether we see a pulsar depends on the Whether we see a pulsar depends on the geometry.geometry. if beam sweeps by Earth’s direction each if beam sweeps by Earth’s direction each
rotation, neutron star appears to be a pulsarrotation, neutron star appears to be a pulsar if polar beam is always pointing toward or if polar beam is always pointing toward or
always pointing away from Earth, we do not always pointing away from Earth, we do not see a pulsarsee a pulsar
Neutron Stars as Neutron Stars as Gamma Ray Bursters!Gamma Ray Bursters!
We sometimes see incredibly powerful, We sometimes see incredibly powerful, and INCREDIBLY short bursts of gamma and INCREDIBLY short bursts of gamma ray radiation.ray radiation.
GRBs > 2 seconds ~ supernova and GRBs > 2 seconds ~ supernova and collapse to a black holecollapse to a black hole
GRBs < 1 second ~ GRBs < 1 second ~ collision of TWO merging neutron stars?
KEY “Key Terms” KEY “Key Terms”
Chandrasekhar limitcosmic rayglitchhelium shell flashhelium shell fusionlighthouse modelneutron degeneracypressureneutron star
nova (plural novae)nucleosynthesisplanetary nebulapulsar
supernovawhite dwarfX-ray burster
Related Documents
