Stellar End-States…

1. Stellar End-States… Now, my suspicion is that the Universe is not only queerer than we suppose, but queerer than we can suppose. J. B. S. Haldane (1892 – 1964) from Possible Worlds, 1927

2. 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?

3. 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?

4. 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?

5. The Evolution of 1Mo Star • 90% of Life as “Main Sequence” star • Fuses Hydrogen to Helium

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

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

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

10. The Evolution of 1Mo Star • Not large enough to fuse Carbon to heavier elements! • Central core eventually collapses • Outer layers gradually “blow” off • Forms a planetary nebula “death shroud” • Core collapsefinally stops as white dwarf

11. Planetary Nebulae “Death Shrouds” of ejected gas surrounding collapsed white dwarf corpse (Not “planets”!)

12. Planetary Nebulae “Death Shrouds” of ejected gas surrounding collapsed white dwarf corpse (Not planets!)

16. Model of Planetary Nebula seen almost edge-on

19. The Evolution of 1Mo Star • Forms a planetary nebula “death shroud” • Core collapsefinally stops as white dwarf • Stellar “corpse” is stable, tiny, hot…... • Supported by electron degeneracy pressure

20. Sirius & White Dwarf

21. Sirius & White Dwarf In X- Rays Note better Resolution!

22. What supports weight of 1Mo star? • Forming as a protostar!: • Thermal pressure < gravity! (collapsing!) • Pressure depends on temperature • Fusing H to He as “main-sequence” star: • Radiation/Gas pressures = gravity (stable!) • Pressure depends on temperature

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

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

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

26. White Dwarfs • Very dense; 0.5 - 1.4 M packed into a sphere the size of the Earth!

27. White Dwarfs • Degenerate matter obeys different laws of physics. • The more mass the star has, the smaller the star becomes! • increased gravity makes the star denser • greater density increases degeneracy pressure to balance gravity

28. Limit on White Dwarf Mass • Predicted gravity will overcome electron degeneracy pressure if white dwarf mass greater than 1.4 M Chandrasekhar Limit Subrahmanyan Chandrasekhar (1910-1995)

29. What if end-state core is larger? • Degeneracy applies to nuclear particles, too! • 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!

30. Nova! Peak Brightness 2 months later 50,000 times dimmer!

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

33. Recurrent Novae

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

35. Even Larger Stars –Ferraris!

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

37. The Periodic Table of Elements!

38. Periodic Table Abundances

39. Periodic Table Abundances Atomic Masses H = 1 He = 4 C = 12 O = 16 N = 20 Mg = 24 Si = 28 S = 32 Fe = 56

40. Supermassive stars lose mass even before they blow up!

41. SUPERNova!

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

45. Neutron Star THEORY • Leftover cores from supernova explosions • Supported by neutron degeneracy pressure • Very TINY1.5 M with 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 G11.20.3.

46. Neutron Star THEORY • Very DENSE:(1012 g/cm3 ) & HOT • Very rapid Rotation: Period = 0.03 to 4 sec • VERY strong Magnetic fields: 1013x 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 G11.20.3.

47. Neutron Star THEORY

48. 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. Determined it was 300 pc away. They called it a “pulsar”, but what was it? Discovery of 1st Pulsar

49. 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.