Dirt and Stars

1
Dirt and Stars

• The Life of a Star
• Dirt, Nebulae
• Collapse
• proto-stars and stars

2
Caterpillars, dirt and butterflies

• The interstellar medium - a dirty place!
• Consists of gas and dust (dirt type stuff)
• What is there to do in space for dirty things?
• Sit around ( redden incoming radiation hide
  things)
• Perform photon screenings (in some cases only
  certain
• polarized types of photons get to move on thru).
• 3. Suck up a bit and start doing some emitting,
  maybe a
• little absorbing.
• 4. Some gas clouds will actually get on with
  their lives
• collapse, swirl around some, get lumpy and
  eventually form
• Stars (butterflies) with little planets swinging
  around them.

Stage 1
3
Speaking of Star Formation

• The molecular cloud collapses into many stars.
• It fragments into many clumps.
• These clumps can further collapse to form stars.
  10 - 1000 stars can be formed from the cloud.

4
More Star formation

• When a fragment of a molecular cloud reaches a
  critical mass, it collapses to form a star. Stage
  2
• Gas and dust are pulled together by gravity until
  a star is formed.
• Gravity makes the cloud collapse.
• Two hindrances to collapse, both which favor
  expansion of the cloud
• Internal heating which causes pressure to
  build-up.
• Angular momentum (rotation at high speeds) (ex
  figure skater)
  

http//www.jbpub.com/starlinks/animation_show.cfm?
id19
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Are we there yet?

• Not yet, Joey
• Cloud fragments continuing to collapse
• Potential energy gt
  Kinetic Energy
• Gas particles speed up and collide.
• The temperature increases.
• This causes a pressure build-up which slows (or
  stops) the collapse. Stage 3
• Energy is radiated away.

6
Were getting closer .. Joey
More on Stage 3 The cloud fragment has
collapsed into a central core surrounded by a
disk of lumpy like material. Our fragment
somewhat resembles a star.
7
And closer
Due to proto-stellar wind and strong heating
Orion Nebula proto-stellar disk
8
And were here, we are a Star !

• The proto-star (which now has a surface
  photosphere) continues to shrink. The central
  core heats up to millions of degrees.
• Collapse is halted by the pressure of the heated
  gas and radiation which counteracts gravity.
• Pressure is force in outward direction, gravity
  is force pulling star in.
• An equilibrium is reached between opposing
  forces.
• Fusion reactions start gt A star is born ! Stage
  5/6

Stage 4

Forces in balance gt no collapse or expansion
Commence fusion!
9
Evolution of 1 Star (better yet, lets see if
this link works.)
file///E/Chaisson/AT419/HTML/AT41902.HTMAnchor-
23240
10
Pretty picture
The Pleiades star cluster. 120 pc away, It is
an Open Cluster a cluster lying in the plane
of the Milky Way, may have a 100 to 10,000
stars these 6 to 7 stars have just been booted
out of The Main Sequence neighborhood! Everyone
in this cluster is about the same age. Young
bunch 100 million years old.