1. Ch. 9 The Lives of Stars from Birth through Middle Age The Cone Nebula

2. Milky Way Photo, showing dark clouds and nebula

3. Interstellar matter Gas and dust Dust grains about 10 -7 m in diameter, about the size of smoke particles Dust causes reddening of the light that passes through it, but NOT redshift. This is due to absorption of the blue components of light (more-so in UV).

4. Light Reddening due to absorption by dust.

5. Light from a star has some absorption lines due to the chromosphere.

6. Additional light reddening is due to absorption by dust.

8. 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%).

9. Detail of Trifid nebula, showing a pillar of cold molecular gas, & a jet coming out of a hidden star, which is about 0.5 parsec long. Expand this some.

10. detail of EGGs: Evaporating Gaseous Globules these can be seen as pillars and egg-like objects

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. Figure 11.9 Emission Nebula Spectrum

13. Radio Emission reveals the dark dust cloud.

14. Horsehead Nebula (neck is about 0.25 pc across) A reflection nebula is seen to the lower left of the horsehead.

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

16. Hydrogen 21-cm Emission (shortwave radio)

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

18. Molecular Cloud Complexes in outer portion of the Milky Way galaxy, looking away from the center. This is a false-color image which corresponds to the intensity of the emission from CO gas. The density in these molecular clouds can be a million times the average, or about one million molecules per cubic centimeter.

19. 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

20. Orion Nebula, Up Close

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

22. Several disks that may be protoplanetary disks are found after blowing up the Hubble photo.

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. Interstellar Cloud Evolution toward a protostar.

25. Stages of evolution of a star like the Sun

26. 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

27. 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”