1. Phys./Geog. 182 Week 7 – Mon. - The Birth of Stars
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. 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%).

5. Interstellar Clouds: A Milky Way mosaic shows dark clouds.

6. A third of the Milky Way Mosaic.

7. Another third of the Milky Way Mosaic.

8. Another third of the Milky Way Mosaic.

9. Galactic Plane, showing several nebulae.
blow up this
small frame

10. M20–M8 Region
blow up this
small frame

11. M20 (Messier 20) The Trifid Nebula

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

13. 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.
Blow up the
upper-left corner.

14. 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.

15. 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.

16. Emission Nebulae Ultraviolet light causes hydrogen to glow with a pinkish color. The detail is in false colors. See the following slides for blowups of these.

17. M8 – The Lagoon Nebula

18. M8 – The Lagoon Nebula

19. M8 – The Lagoon Nebula – detail in false color

20. from the Hubble
website:

21. M16 - The Eagle Nebula

22. M16 - The Eagle Nebula, in visible light

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

24. 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”

25. EGGs –
Evaporating
Gaseous
Globules
These
can be
seen as
pillars and
egg-like
objects.

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

27. finer detail of these
EGGs:
Evaporating
Gaseous
Globules

28. 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.

29. Emission Nebula Spectrum

30. Dark Dust Clouds: Obscuration and Emission
more on next slides

31. Dark Dust Clouds: not just an absence of stars!

32. Radio Emission reveals the dark dust cloud.

33. Dark Dust Cloud, seen in visible light.

34. Dark Dust Cloud revealed in infrared photo

35. Horsehead Nebula (neck is about 0
Horsehead Nebula (neck is about 0.25 pc across) The pink nebulae are emission nebulae.

36. Horsehead Nebula (neck is about 0
Horsehead Nebula (neck is about 0.25 pc across) A reflection nebula is seen to the lower left of the horsehead.

37. Horsehead Nebula (The neck is about 0
Horsehead Nebula (The neck is about pc across) A nice example of a dark dust cloud

38. 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

39. Atomic Motions are rarely influenced by gravity
Atomic Motions are rarely influenced by gravity. They just keep colliding and coming apart. When there are enough in a cloud to equal the mass of the sun, and temperature is about 100 K, the entire cloud can start to shrink due to its own weight, and we get stage 1 of star formation. (The “collapse” of a cloud is probably “triggered” by some event in nearby space.)

40. Stage 2: Cloud Fragmentation probably occurs Fragments may contain one to several solar masses of molecular gas and dust.

41. Orion Nebula, Up Close

42. Orion Nebula is located in the “sword” of several objects hanging below the “belt” of Orion.

43. Orion Nebula, Up Close

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

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

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

47. A protostar can be plotted on the H–R diagram after reaching stage 4
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 times as luminous as our Sun, mostly in the infrared part of the spectrum.

48. 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

49. Protostellar Outflow

50. Protostars in Orion region top: low-mass protostar with solar-system- sized dusty disk bottom: more evolved disk around a protostar

51. 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”

52. FIGURE 12-12 Pre–Main-Sequence Evolutionary Tracks
This H-R diagram shows evolutionary tracks based on models of
seven stars having different masses. The dashed lines indicate
the stage reached after the indicated number of years of evolution.
The birth line, shown in blue, is the location where each
protostar stops accreting matter and becomes a pre–mainsequence
star. Note that all tracks terminate on the main
sequence at points that agree with the mass-luminosity relation
(see Figure 11-14a).

53. Brown Dwarfs are “failed stars” This one has a mass of about 50 times that of Jupiter.
The line
is a
CCD
glitch

54. 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”).

55. H-R diagram of the Pleiades Open Cluster