Stellar evolution, energy generation and star clusters

1
Stellar evolution, energy generation and star
clusters

• section 11

2
Problem 1

• The following statements relate to star
  formation. Which ones of these statements are
  false?
• I. During the process of star formation, a giant
  molecular cloud collapse to form a single star.
• II. Molecular cloud collapse can be initiated by
  shock waves from distant supernova explosions.
• III. The rotation of a collapsing molecular cloud
  causes it to collapse faster.
• IV. Internal heating and pressure build-up causes
  a molecular cloud to collapse more slowly.
• V. A disk of material will generally form
  parallel to the axis of rotation of a contracting
  protostar.

3
I. False!!!

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

4
Problem 1

• The following statements relate to star
  formation. Which ones of these statements are
  false?
• I. During the process of star formation, a giant
  molecular cloud collapse to form a single star.
• II. Molecular cloud collapse can be initiated by
  shock waves from distant supernova explosions.
• III. The rotation of a collapsing molecular cloud
  causes it to collapse faster.
• IV. Internal heating and pressure build-up causes
  a molecular cloud to collapse more slowly.
• V. A disk of material will generally form
  parallel to the axis of rotation of a contracting
  protostar.

5
II. True

• there are 3 methods
• Accretion
• Gravity and Radiation Pressure
• compression by SN blast waves

6
Problem 1

• The following statements relate to star
  formation. Which ones of these statements are
  false?
• I. During the process of star formation, a giant
  molecular cloud collapse to form a single star.
• II. Molecular cloud collapse can be initiated by
  shock waves from distant supernova explosions.
• III. The rotation of a collapsing molecular cloud
  causes it to collapse faster.
• IV. Internal heating and pressure build-up causes
  a molecular cloud to collapse more slowly.
• V. A disk of material will generally form
  parallel to the axis of rotation of a contracting
  protostar.

7
III. False (?)

• Gravity makes the cloud collapse
• Angular momentum favors expansion of the
  cloud...why?
• L mvr
• Conservation of L as the cloud fragment shrinks
  due to gravity, it spins faster.
• Collapse occurs preferentially along path of
  least rotation.
• The cloud fragment collapses into a central core
  surrounded by a disk of material.

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Problem 1

• The following statements relate to star
  formation. Which ones of these statements are
  false?
• I. During the process of star formation, a giant
  molecular cloud collapse to form a single star.
• II. Molecular cloud collapse can be initiated by
  shock waves from distant supernova explosions.
• III. The rotation of a collapsing molecular cloud
  causes it to collapse faster.
• IV. Internal heating and pressure build-up causes
  a molecular cloud to collapse more slowly.
• V. A disk of material will generally form
  parallel to the axis of rotation of a contracting
  protostar.

9
IV. True

• Internal heating causes pressure build-up
• Cloud fragments collapse
• Potential energy Kinetic Energy
• Gas particles speed up and collide.
• The temperature increases.
• This causes a pressure build-up which slows (or
  stops) the collapse.
• Energy is radiated away.

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Problem 1

• The following statements relate to star
  formation. Which ones of these statements are
  false?
• I. During the process of star formation, a giant
  molecular cloud collapse to form a single star.
• II. Molecular cloud collapse can be initiated by
  shock waves from distant supernova explosions.
• III. The rotation of a collapsing molecular cloud
  causes it to collapse faster.
• IV. Internal heating and pressure build-up causes
  a molecular cloud to collapse more slowly.
• V. A disk of material will generally form
  parallel to the axis of rotation of a contracting
  protostar.

11
V.False!
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Problem 2

• Answer the following questions
• a) By what two processes is energy transported in
  stars undergoing fusion?
• b) On what part of the HR diagram are stars
  primarily converting Hydrogen to Helium?
• c) Consider the following two star clusters
  Cluster A contains few O or B type stars, while
  Cluster B contains mostly G, K, and M type stars.
  Which cluster is older and why?

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a)

• Energy can be transported by conduction,
  convection, radiation
• Stars use the latter two methods
• The trade between convection and radiation
  depends on the star and region within a star

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Problem 2

• Answer the following questions
• a) By what two processes is energy transported in
  stars undergoing fusion?
• b) On what part of the HR diagram are stars
  primarily converting Hydrogen to Helium?
• c) Consider the following two star clusters
  Cluster A contains few O or B type stars, while
  Cluster B contains mostly G, K, and M type stars.
  Which cluster is older and why?

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b) Main Sequence
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Problem 2

• Answer the following questions
• a) By what two processes is energy transported in
  stars undergoing fusion?
• b) On what part of the HR diagram are stars
  primarily converting Hydrogen to Helium?
• c) Consider the following two star clusters
  Cluster A contains few O or B type stars, while
  Cluster B contains mostly G, K, and M type stars.
  Which cluster is older and why?

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c)

• O and B stars spend less time in the Main
  sequence they are bigger and hotter than late
  type stars (K,M) so they burn they fuel faster.
• Assuming that all type of stars are were present
  when the cluster form, then if the 2nd cluster
  does not have O or B stars that means that these
  stars already escape from the main sequence, so
  the 2nd cluster is older.