1. Chapters 12 and 13: Chapters 12 and 13: The Lives and Deaths of Stars - Stellar Evolution NGC 2264

2. 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?

3. You will discover… The remarkable transformations of older stars into giants and supergiants. The remarkable transformations of older stars into giants and supergiants. That some dying stars eject material that creates new generations of stars, while others act as beacons that enable astronomers to pinpoint distant galaxies. That some dying stars eject material that creates new generations of stars, while others act as beacons that enable astronomers to pinpoint distant galaxies.

4. 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.

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

6. HR Diagram (Main Sequence = the red line). Main Sequence Star definition: 1. Star is fusing Hydrogen to Helium in its core. 2. Star is not expanding or contracting.

7. If a star is above or below the Main Sequence, then something else is going on. We need to find out what that is.

8. What if our Sun were 1.5 times as big as it is? What if the Sun were 3 times bigger? 10 6 years = 1 million years

9. Summary 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.  Big stars (8-25 times the Sun’s mass).  Huge stars (more than 25 times the Sun’s mass). Stars like our Sun (M O = 1) will turn into Planetary Nebulae and White Dwarf Stars, then end up as Black Dwarfs that give off no light. Stars like our Sun (M O = 1) will turn into Planetary Nebulae and White Dwarf Stars, then end up as Black Dwarfs that give off no light. Big stars (8-25 M O ) will end up as Neutron Stars. Big stars (8-25 M O ) will end up as Neutron Stars. Huge stars (>25 M O ) will end up as Black Holes. Huge stars (>25 M O ) will end up as Black Holes.

10. Summary of Stellar Evolution The evolution of stars depends on their masses.

11. Stars Like Our Sun (M O = 1) Main Sequence Main Sequence Red Giant Red Giant Red Supergiant Red Supergiant Planetary Nebula and White Dwarf Planetary Nebula and White Dwarf Black Dwarf Black Dwarf

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

13. The Sun Today and as a Red Giant

14. Red Giant Stars in a Star Cluster

15. Life History of Stars Like Our Sun 1.Main Sequence 2.Red Giant 3.Red Supergiant 4.Planetary Nebula and White Dwarf 5.Black Dwarf

16. Our Sun in Old Age – a Red Supergiant Near the end of its life, the Sun will become a Supergiant.

17. From 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.

18. It might look like this (Helix Nebula)

19. More Planetary Nebulae

20. Sirius’s White Dwarf Friend Sirius B, a white dwarf, at the five o’clock position Both emit X-rays

21. Big Stars and Huge Stars (8-25 M O ) (>25 M O ) Main Sequence Main Sequence Bright Supergiant Bright Supergiant Supernova Explosion Supernova Explosion Big Star → Neutron Star Big Star → Neutron Star Huge Star → Black Hole Huge Star → Black Hole

22. Structure of Big and Huge Stars in Old Age – a Bright Supergiant The old star’s core is now made of Iron. Oops!

23. Disaster is not far away. The Supergiant’s core is made of Iron, which cannot be “burned” to make any heavier elements. The Supergiant’s core is made of Iron, which cannot be “burned” to make any heavier elements. So the star’s core collapses because of gravity, then rebounds, and the star explodes. So the star’s core collapses because of gravity, then rebounds, and the star explodes. We have a Supernova Explosion. We have a Supernova Explosion.

24. HOW FAST DOES ALL THIS HAPPEN?

25. Supernovae Make a Mess Computer simulations showing how chaotic the supernova is deep inside the star as it begins to explode.

26. A Supernova Remnant X-ray image of the Cygnus Loop HST image of the Cygnus Loop

27. Gum 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.

28. Supernova 1987A (LMC)

29. Big and Huge Stars – the Final Stage Neutron Stars result from Supernova Explosions of Big Stars. Neutron Stars result from Supernova Explosions of Big Stars. Black Holes result from Supernova Explosions of Huge Stars. Black Holes result from Supernova Explosions of Huge Stars.

31. Neutron 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.

32. Neutron Stars How Big? How Dense? A typical Neutron Star would fit between Loyola Academy and Chicago’s Loop. A typical Neutron Star would fit between Loyola Academy and Chicago’s Loop. One teaspoonful of Neutron Star material would weigh one billion tons on Earth. One teaspoonful of Neutron Star material would weigh one billion tons on Earth.

33. A 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.

35. Radio Signals or X-rays from a Pulsar

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

37. Colliding Neutron Stars Collisions of Neutron Stars may cause creation of elements heavier than Iron, such as Gold, Silver, Platinum, Uranium. Collisions of Neutron Stars may cause creation of elements heavier than Iron, such as Gold, Silver, Platinum, Uranium. You can thank the stars for your jewelry, as well as for the elements you are made of (Carbon, Oxygen, Phosphorus, Nitrogen, Iron, etc.). They made it all from Hydrogen. You can thank the stars for your jewelry, as well as for the elements you are made of (Carbon, Oxygen, Phosphorus, Nitrogen, Iron, etc.). They made it all from Hydrogen.

38. Black Hole

39. Summary of Stellar Evolution The evolution of stars depends on their masses.

40. Summary of Stellar Evolution The evolution of stars depends on their masses. The evolution of stars depends on their masses. Stars like our Sun (M O = 1) will turn into Planetary Nebulae and White Dwarf Stars, then end up as Black Dwarfs that give off no light. Stars like our Sun (M O = 1) will turn into Planetary Nebulae and White Dwarf Stars, then end up as Black Dwarfs that give off no light. Big stars (8-25 M O ) will end up as Neutron Stars, after a Supernova Explosion. Big stars (8-25 M O ) will end up as Neutron Stars, after a Supernova Explosion. Huge stars (>25 M O ) will end up as Black Holes, after a Supernova Explosion. Huge stars (>25 M O ) will end up as Black Holes, after a Supernova Explosion. Material from old stars (Planetary Nebulae, Supernova Remnants, etc.) gets recycled to form new stars. Material from old stars (Planetary Nebulae, Supernova Remnants, etc.) gets recycled to form new stars.

41. Stars – The Ultimate Recyclers Material from old stars (Planetary Nebulae, Supernova Remnants, etc.) gets recycled to form new stars.

42. WHAT DID YOU THINK? How do stars form? How do stars form? Stars form from the mutual gravitational attraction between gas and dust inside giant molecular clouds. Stars form from the mutual gravitational attraction 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 on the main sequence, as well as infrared images of gas and dust clouds in the process of forming stars. Yes. Astronomers have seen stars that have just arrived on the main sequence, as well as infrared images of gas and dust clouds in the process of forming stars. Do stars with greater mass shine longer? Do stars with greater mass shine longer? No. Lower-mass stars last longer because the lower gravitational force inside them causes fusion to take place at slower rates compared to the fusion inside higher-mass stars. No. Lower-mass stars last longer because the lower gravitational force inside them causes fusion to take place at slower rates compared to the fusion inside higher-mass stars.

43. 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.

44. STELLAR EVOLUTION (star types are underlined) 1. OUR SUN Object (and transition)What's HappeningOther Stuff OUR SUNHydrogen core fusionlifetime = 10 Billion years ↓(makes Helium core) RED GIANTHydrogen shell fusionsize = out to Venus, toasts Earth ↓(Helium core flash) shrinksHelium core fusion ↓(makes Carbon & Oxygen core) RED SUPERGIANTHelium shell fusionsize = out to Earth's orbit ↓(Helium shell flash) PLANETARYmade of dust & gasstar's outer layers "puff off” NEBULAand WHITE DWARFmade of Carbon & Oxygensize = the Earth ↓(cools off) BLACK DWARFgives off no light

45. 2. BIG STARS (8-25 times Sun's mass) and HUGE STARS (more than 25 times Sun's mass) ObjectWhat's Happening and Other Stuff BIG STARSlifetime = 15 Million years and HUGE STARSlifetime = 3 Million years ↓(fusion of Hydrogen, Helium, Carbon, and Oxygen - makes Iron core) BRIGHT SUPERGIANTSsize = out to Jupiter's orbit or bigger ↓ SUPERNOVA EXPLOSIONstar collapses, rebounds, explodes ↓ BIG STARS end up as NEUTRON STARSmade of Neutrons & other stuff, size = Chicago HUGE STARS end up as BLACK HOLESgravity is so strong that light cannot escape