Stellar Evolution

1. Stellar Evolution The Stars: Part C Interstellar Medium The Lives and Deaths of Stars Neutron Stars and Black Holes

2. The Interstellar Medium • What exists in the space between stars? • Gas- Atoms and Molecules 90% Hydrogen 9% Helium 1% Heavy Elements Less than one atom per cm3. • Dust- Particulate (Clumps of atoms and molecules) • Not well know • Silicates, Carbon, Iron, “Dirty Ice”

3. The Interstellar Medium • Dark Regions • Foreground Dust Clouds Block Light

4. Interstellar Clouds • Fuzzy Patches of Light

6. Interstellar Clouds • Emission Nebula- • Glowing Clouds of Hot Interstellar Matter • At the center of each is a newly formed “Hot” O or B-type star. • The Strong UV emissions of the central star Ionize the surrounding gas cloud, making it glow.

7. Interstellar Clouds • Flame Nebula

8. Interstellar Clouds • Rosette Nebula

9. Interstellar Clouds • Eagle Nebula • Pillars of Creation

10. Interstellar Clouds • Lagoon Nebula

11. Interstellar Clouds • Many Nebulae have dark regions • “Dust Lanes” • Trifid Nebula • Emission Nebulae are only a small percentage of the total interstellar space.

12. Interstellar Clouds • Some Clouds are denser than the typical vacuum but very low temperature (10’s of K) • Dark Dust Clouds

13. Interstellar Clouds • Horsehead Nebula • Dark Dust Cloud Silhouetted against an Emission Nebula

14. Formation of Sun-Like Stars • Stars form from the gas and dust in the Interstellar Medium • Small Clumps of Matter • Enough matter that gravity prevents dispersion • Triggered by an external event • Heating from hot nearby stars • Nearby supernova explosions

15. Formation of Sun-Like Stars • Stage 1- An Interstellar Cloud • Huge Cloud (10’s of pc across) • Mostly Cold Atomic Gas • “Event” triggers variation in densities • Cloud Segments begin to fragment and collapse

16. Formation of Sun-Like Stars • Depending on Fragmentation, one cloud can form • Dozens of High Mass Stars • Hundreds of Sun-Like or smaller stars • Process takes Several Million Years • Stage 2- Gas Cloud Fragment • 100x the size of our solar system • Still Cold- 100K (-173oC) at the center • (Low Density = Transparent to radiation) • Collapse Continues for 10,000’s of years

17. Formation of Sun-Like Stars • Stage 3- Collapsing Fragment/Protostar • Cloud is the Size of our Solar system • Internal Temp increase to 10,000K • (More Dense = Opaque to radiation) • Increasing Mass, Decreasing Size • Gravity > Pressure • End of Stage 3- Protostar

18. Formation of Sun-Like Stars

19. Formation of Sun-Like Stars • Stage 4- Protostar • About 100,000 years after fragment formed • Now has Photosphere • Internal Temp is 1 Million K • (Still short of 10 Million K needed to ignite Fusion) • Size of Mercury’s Orbit (100x Ro) and collapsing • Matter still raining down from solar nebula

20. Formation of Sun-Like Stars • Stage 4 Can now be Plotted on the H-R Diagram • Based on- • Luminosity • Temperature

21. Formation of Sun-Like Stars • Stage 5- Protostellar Evolution • Still not in Equilibrium • Contraction is slowing • Now only 10x Ro • Int. Temp 5 Million K • Surface Temp 4000 K • Violent Stage • Strong Solar Wind • Bipolar Jets of Matter

22. Formation of Sun-Like Stars • Stages 2-5 Occur Rapidly (100,000’s of years) • At stage 5 Evolution slows • After ~ 10 Million Years from first appearance… • Stage 6- A Newborn Star • Int. Temp Reaches 10 Million K • Surface Temp is 4500 K • Fusion Begins

23. Formation of Sun-Like Stars • Stage 7- Main Sequence • Another 30 Million Years • Int. Temp Increases to 15 Million K • Surface Temp reach 6000 K • Gravity = Pressure (Eqm) • Our Sun… or just like it.

24. Formation of Sun-Like Stars

25. Formation of Sun-Like Stars

26. Stars of Other Masses • Higher Mass Stars • Formation happens faster • Form Higher on Main Sequence • Lower Mass Stars • Formation happens slower • Form Lower on Main Sequence • Emission Nebula are so important

27. Stars of Other Masses

28. Stars of Other Masses • “Failed” Stars • Not Enough Mass • Reaches Equilibrium before Temperature reaches 10 Million K (Fusion) • Never move past the Protostar Phase • Continually cooling • “Brown Dwarfs” • Minimum Mass 0.08 Solar Masses (80x Jupiter)

29. Stars of Other Masses

30. Star Clusters • Single Cloud • Segments • Forms Many Stars… • In the same area • Of the same composition • At the same time • Excellent “Controlled Experiment” • Compare stars solely by their masses.

31. Star Clusters • Open Clusters – • 100’s up to 10,000’s of Stars • Stars on all parts of the Main Sequence • Tells us it is a “young” formation • Less than 20 Million Years (O type star lifespan) • Pleiades- The Seven Sisters • Open star Cluster in Constellation Taurus

33. Star Clusters • The Nebular wisps surrounding the stars add to the evidence of its young age. • Note the name of the cluster in Japanese… • Subaru

34. Star Clusters • Globular Clusters- • Up to Millions of Stars • Spherical In Shape • Much Older Clusters (10 Billion years old) • No Upper Main Sequence stars • No stars Larger than 0.8 Sun’s Mass

36. Star Clusters • Omega Centauri • Nearly all stars are • low mass main sequence • older stars entering red giant phases of stellar evolution

37. Star Clusters • Star Clusters and Emission Nebulae • First High Mass Stars • Form quickest • Ionize surrounding Cloud • Prevent formation of other high mass stars • Strong Wind • Radiation • Low Mass Stars visible in Infrared

38. Star Clusters • Orion Nebula