1. Ch. 9 The Lives of Stars from Birth through Middle Age The Cone Nebula Quick review of Tuesday’s lecture

2. Interstellar gas The interstellar gas is very dilute, about ONE atom per cubic centimeter. In some places it is much denser. The distribution of gas is very uneven. It is mostly Hydrogen (90%), Helium (9%), and everything else (1%).

3. Dense regions of gas form Interstellar Clouds: A Milky Way mosaic shows many dark clouds.

4. Trifid nebula, taken with ground-based telescope. Insert shows field of view of Hubble wide-field camera.

5. Detail of the Trifid nebula, showing a pillar of cold molecular gas. A jet coming out of a hidden star is about 0.5 parsec long.

6. M16 - The Eagle Nebula, in visible light - close up of pillar region.

7. M16 - The Eagle Nebula – the pillars in false color, from the Hubble Space Telescope. Blow up this corner, and rotate it. These are sometimes called the “Pillars of Creation”

8. EGGs – Evaporating Gaseous Globules We see pillars and egg-like objects.

9. EGGs: Evaporating Gaseous Globules Some of these may contain newly- forming stars.

10. finer detail of these EGGs: Evaporating Gaseous Globules We also see gas evaporating from the pillar.

11. Some properties of these nebulae: note that these are AVERAGE quantities; the nebulae are actual quite uneven in their density and temperature. Note the huge masses and sizes.

12. Dark Dust Clouds are not just an absence of stars!

13. Radio Emission reveals the dark dust cloud. Some also show up in infrared (IR) photos.

14. Horsehead Nebula (The neck is about 0.25 pc across) A nice example of a dark dust cloud

15. Molecules near M20, a visible photo is overlaid with a contour plot of 21 cm radio intensity This cold dark cloud is probably in stage 1 of star formation

16. Star formation – a 7 stage process 1 – an interstellar cloud 2 – shrinking cloud fragments 3 – a fragment is the size of our solar system 4 – protostar center reaches 1,000,000 K 5 – protostar at ~10 solar radius, 4000K surf. 6 – ignition of fusion in core, now a star 7 – reaches main sequence

17. Stage 2: Cloud Fragmentation occurs due to one of several causes. The fragments may contain one to several solar masses of molecular gas and dust.

18. Orion Nebula A closer look reveals “knots” or EGGs, some of which may contain protostars.

19. These globules may contain evolving planets as well as the central protostar.

20. Proplyds Several objects that may be protoplanetary disks are found after blowing up the Hubble photo.

21. IR photos may reveal protostars inside the dark clouds.

22. Interstellar Cloud Evolution toward a protostar.

23. A protostar can be plotted on the H–R diagram after reaching stage 4. It is heated solely due to contraction and is fairly cool, but might be 1000 times as luminous as our Sun, mostly in the infrared part of the spectrum.

24. Newborn Star on the H–R Diagram Stage 5 – T Tauri stage – has violent surface activity and may form “jets” Stage 6 – core at 10 million K and finally get fusion Stage 7 – reaches the main sequence

25. Protostellar Outflow

26. Prestellar Evolutionary Tracks for stars of other masses The minimum mass needed to get nuclear fusion and produce a real star is about 0.08 solar mass, or about 80 times the mass of Jupiter. With less mass all we get are “brown dwarfs”

28. We believe that most stars form in clusters from a single large cloud that fragments. An example of an Open Cluster is the Pleiades cluster (M45, a.k.a. “the seven sisters”).

29. H-R diagram of the Pleiades Open Cluster