1. Astrophysics I: The Stellar Lifecycle Kathy Cooksey

2. How to Make a Star Collapse interstellar clouds

3. Visible and IR image of the hot protostars in Orion Nebula.

4. How to Make Systems Cloud around protostar spins faster Flattens to a disk –Think pizza dough

5. Protostars and Disks Dust and gas condense onto dust grains Small clumps grow bigger Bigger clumps have more mass and attract more matter Planetesimals become building blocks of planets Orion Nebula – Copyright O’Dell and Wong

6. Now what? Mass of the star determines rest of its life! More massive star  more pressure in core More pressure  more fusion More fusion: –More energy produced –Hotter –Shorter life span

7. Stellar Evolution The Life of a Star (like our Sun) (which does not move in a circle as it evolves  Artist’s rendition)

8. The Main Sequence Balance between: –Force of gravity pulling in –Pressure from the heat of fusion pushing out Stars on main sequence burn hydrogen in their core to produce heat Longest phase of a star’s life

9. What then? Gravity-pressure balance disturbed when hydrogen in core depleted Big change in structure and appearance of the star “THE END” depends on star’s mass Two cases: –Low-mass (< 8  mass of Sun) –High-mass (> 8  mass of Sun)

10. Red Giants After hydrogen exhausted in core: Core collapses, releasing energy to outer layers Outer layers expand Increasing temperature and pressure in core  helium fuses

11. The End for Low Mass Stars Core is contracting and heating. –Surface is cooling and expanding. Will it finally become hot enough in core for Carbon to fuse? –For the Sun: No. Gravity keeps contracting the core: 1000 kg/cm3! What stops it? –Electron degeneracy pressure!

12. Electron Degeneracy Pressure from motion of atoms

13. Electron Degeneracy Pressure from electron shells

14. Where are we now? Core dead – nothing happening. Shells – burning H and He, but soon stop too. Outside atmosphere of star still cooling and expanding. …and expanding Force of radiation from burning shells blows atmosphere away.

15. M57 – Ring Nebula

16. White Dwarfs Leftover once atmosphere blows away Exposed electron degenerate carbon core Size of Earth No more fusion Glow by their heat alone Eventually cool and fade away  black dwarf

17. High-Mass Stars H and He burned in core Core collapses hot enough to fuse heavier elements (C, N, O …) Iron is most stable element and cannot be fused further –Instead of releasing energy, it uses energy

18. End for High Mass Stars Fuel runs out Core collapses and rebounds Supernova! Matter thrown back into the interstellar medium Matter rushing outwards, fuses with matter rushing inwards Every element heavier than iron is made in instant of supernova!

19. We are stardust!

20. About the core…

21. First Stop: Electron Degeneracy

22. Last Stop: Neutron Degeneracy

23. Otherwise…

24. M1 – Crab Nebula – copyright VLT

25. NGC 4526 – 6 Million parsecs away

26. Stellar Lifecycle Summary Low-mass Stars Like Sun Long lived (measure in billion years) Fuse to mostly helium Planetary nebula and white dwarf end state Most common High-mass Stars 8  more massive Short lived (measure in million years) More fusion (C, N, O …) Supernova and neutron star or black hole end Makes most important elements