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? Will the Sun someday cease to shine brightly? What is a nova? What is a supernova? Where does carbon, silicon, oxygen, iron, uranium, & other heavy elements come from? What is a pulsar?

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… (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 1M o Star 90% of Life as “Main Sequence” star 90% of Life as “Main Sequence” star Fuses Hydrogen to Helium Fuses Hydrogen to Helium

The Evolution of 1M o Star 90% of Life as “Main Sequence” star 90% of Life as “Main Sequence” star Fuses Hydrogen to Helium Fuses Hydrogen to Helium He collects in core & builds up over time He collects in core & builds up over time

The Evolution of 1M o Star He core collapses, triggers expansion to Red Giant He core collapses, triggers expansion to Red Giant Fuses H to He in shell Fuses H to He in shell Eventually fuses He to Carbon in Core Eventually fuses He to Carbon in Core Creates dust grains in outer edges Creates dust grains in outer edges

Stellar Model of a Sun-Like Star A red giant!

The Evolution of 1M o Star Not large enough to fuse Carbon to heavier elements! Not large enough to fuse Carbon to heavier elements! Central core eventually collapses Central core eventually collapses Outer layers gradually “blow” off Outer layers gradually “blow” off Forms a planetary nebula “death shroud” Forms a planetary nebula “death shroud” Core collapse finally stops as white dwarf Core collapse finally stops as white 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 1M o Star Forms a planetary nebula “death shroud” Forms a planetary nebula “death shroud” Core collapse finally stops as white dwarf Core collapse finally stops as white dwarf Stellar “corpse” is stable, tiny, hot…... Stellar “corpse” is stable, tiny, hot…... Supported by electron degeneracy pressure

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 temperature Pressure depends on temperature Fusing H to He as “main-sequence” star: Fusing H to He as “main-sequence” star: Radiation/Gas pressures = gravity (stable!) Radiation/Gas pressures = gravity (stable!) Pressure depends on temperature Pressure depends on temperature What supports weight of 1M o star?

After Red Giant stage? After Red Giant stage? No longer fusing! Electrons to the rescue! Electrons to the rescue! Degeneracy Pressure (Pressure no longer depends on temperature) Degeneracy Pressure (Pressure no longer depends on temperature) What supports weight of 1M o star?

Degeneracy Pressure “Two particles cannot occupy same space with same momentum (energy)” “Two particles cannot occupy same space with same momentum (energy)” For very dense solids, electrons cannot all be in ground states For very dense solids, electrons cannot all be in ground states Electrons become VERY energetic--- velocities approach speed of light. Electrons become VERY energetic--- velocities approach speed of light. Pressure holding up star no longer depends on temperature.

White Dwarfs Stable! Gravitational pressure in = electron degeneracy pressure out Stable! Gravitational pressure in = electron degeneracy pressure out Not fusing: Generates no new energy Not fusing: Generates no new energy Cooling off: Cooling off: Radiates heat into space, getting fainter over time

White Dwarfs Very dense; M  packed into a sphere the size of the Earth! Very dense; M  packed into a sphere the size of the Earth!

White Dwarfs Degenerate matter obeys different laws of physics. Degenerate matter obeys different laws of physics. More massive star => smaller core becomes! More massive star => smaller core becomes! increased gravity makes star denser increased gravity makes star denser greater density increases degeneracy pressure to balance gravity greater density increases degeneracy pressure to balance gravity

Limit on White Dwarf Mass Predicted gravity will overcome electron degeneracy pressure if white dwarf mass greater than 1.4 M  Predicted gravity will overcome electron degeneracy pressure if white dwarf mass greater than 1.4 M  Subrahmanyan Chandrasekhar ( ) Chandrasekhar Limit

Subrahmanyan 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? Degeneracy applies to nuclear particles, too! Degeneracy applies to nuclear particles, too! Collapses until neutron degeneracy pressure holds up the corpse ( Collapses until neutron degeneracy pressure holds up the corpse (neutron star) If even neutron degeneracy can’t support the weight of the core…  Black Hole!

Nova! Peak Brightness2 months later 50,000 times dimmer!

Nova! If white dwarf is part of a close binary: If white dwarf is part of a close binary: Its gravity can pull matter from nearby star Its gravity can pull matter from nearby star Forms an accretion disk around White dwarf Forms an accretion disk around White dwarf Friction heats it Friction heats it If matter falls onto WD, eventually H fusion can begin… If matter falls onto WD, eventually H fusion can begin… White Dwarf suddenly, temporarily gets much brighter…. White Dwarf suddenly, temporarily gets much brighter….

Recurrent Novae

Even Larger Stars –Ferraris! Stars 10x larger than our Sun Stars 10x larger than our Sun Fuse faster! Fuse faster! Shine brighter!! Shine brighter!! Live very short lives… Live very short lives…But… Make every element in your body after Helium!

Even Larger Stars –Ferraris!

Evidence Supporting Theories Periodic Table Abundances Periodic Table Abundances Multiples of “4” match Helium fusion chain Multiples of “4” match Helium fusion chain Neutrinos from Supernova Neutrinos from Supernova SN 1987a caught “early” in explosion SN 1987a caught “early” in explosion Cosmic Rays Cosmic Rays

The Periodic Table of Elements!

Periodic 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!

Neutron Stars What is a neutron star? (THEORY) What is a neutron star? (THEORY) What is a pulsar? (OBSERVATION) What is a pulsar? (OBSERVATION) What evidence do we have that they are one in the same? What evidence do we have that they are one in the same?

Neutron Star THEORY Leftover cores from supernova explosions Leftover cores from supernova explosions Supported by neutron degeneracy pressure Supported by neutron degeneracy pressure Very TINY 1.5 M  with a diameter of 10 to 20 km Very TINY 1.5 M  with a diameter of 10 to 20 km Chandra X-ray image Chandra X-ray image of the neutron star left behind by a supernova observed in A.D The remnant is known as G11.2  0.3.

Neutron Star THEORY Very DENSE: (10 12 g/cm 3 ) & HOT Very DENSE: (10 12 g/cm 3 ) & HOT Very rapid Rotation: Period = 0.03 to 4 sec Very rapid Rotation: Period = 0.03 to 4 sec VERY strong Magnetic fields: x Earth’s. VERY strong Magnetic fields: x Earth’s. Chandra X-ray image Chandra X-ray image of the neutron star left behind by a supernova observed in A.D The remnant is known as G11.2  0.3.

Neutron Star THEORY

Discovery of 1 st Pulsar In 1967, graduate student Jocelyn Bell and her advisor Anthony Hewish accidentally discovered a radio source in Vulpecula. In 1967, graduate student Jocelyn Bell and her advisor Anthony Hewish accidentally discovered a radio source in Vulpecula. 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 “pulsar”, but what was it? They called it a “pulsar”, but what was it?

The Crab Pulsar The mystery was solved when a pulsar was discovered in the heart of the Crab Nebula. The Crab pulsar also pulses in visual light.

Pulsar Observations Very tiny pulse “width” Very 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 energy Very regular pulse of energy Occasional “Glitches” in signal Occasional “Glitches” in signal A few seen in X-ray binary systems A few seen in X-ray binary systems High temperatures, large masses High temperatures, large masses

Pulsar Observations Synchotron emission --- non-thermal process where radiation is emitted by charged particles moving close to the speed of light around magnetic fields. Synchotron emission --- non-thermal process where radiation is emitted by charged particles moving close to the speed of light around magnetic fields. Slow down over time Slow down over time Fastest signal oscillation in Supernova Remnants Fastest signal oscillation in Supernova Remnants

Neutron Star = Pulsar!! TheoryObservation 1.TinySmall Pulse Width 2.Rotating FastRegular Pulse up to 1000 times a second 3.Strong Magnetic FieldSynchrotron Radiation 4.Dense, MassiveX-ray Binary accretion disks surround pulsar 5.Supernova CorpseSee in SN Remnants 6.Energy From RotationSlow Down over time

Model of Pulsar as Rotating Neutron Star

“Lighthouse” Model of Pulsar Pulsars are the lighthouses of Galaxy!

Pulsars as Celestial Beacons

Pulsars vs. Neutron Stars? All pulsars are neutron stars, but all neutron stars are not pulsars!! All pulsars are neutron stars, but all neutron stars are not pulsars!! Whether we see a pulsar depends on the geometry. Whether we see a pulsar depends on the geometry. if beam sweeps by Earth’s direction each rotation, neutron star appears to be a pulsar if beam sweeps by Earth’s direction each rotation, neutron star appears to be a pulsar if polar beam is always pointing toward or always pointing away from Earth, we do not see a pulsar if polar beam is always pointing toward or always pointing away from Earth, we do not see a pulsar

Neutron Stars as Gamma Ray Bursters! We sometimes see incredibly powerful, and INCREDIBLY short bursts of gamma ray radiation. We sometimes see incredibly powerful, and INCREDIBLY short bursts of gamma ray radiation. GRBs > 2 seconds ~ supernova and collapse to a black hole GRBs > 2 seconds ~ supernova and collapse to a black hole GRBs < 1 second ~ collision of TWO merging neutron stars? GRBs < 1 second ~ collision of TWO merging neutron stars?collision of TWO merging neutron stars?collision of TWO merging neutron stars?

KEY “Key Terms” KEY “Key Terms” Chandrasekhar limit cosmic ray glitch helium shell flash helium shell fusion lighthouse model neutron degeneracy pressure neutron star nova (plural novae) nucleosynthesis planetary nebula pulsar supernova white dwarf X-ray burster