STAR FORMATION

Is star formation currently ongoing in the Milky Way?
• The Sun will live for ~ 10¹⁰ years. We can derive this number from a simple exercise.
  • How much fuel does the Sun contain?

    The Sun converts mass into energy ==> available fuel = eff x M_Sun x c².
    

  • How fast will the Sun burn this fuel?

    Fuel Consumption rate = Luminosity

    ===> lifetime = Fuel/L = (0.007)x2x10³⁰x(3x10⁸) ²/4x10²⁶ = 3.2x10¹⁷ s = 100 billion years

    The Sun burns only the inner 10 % of its hydrogen during its main sequence lifetime ===> Main Sequence Lifetime = 10 billion years.

• In general, for Main Sequence stars more massive than 0.7 M_Sun,

  lifetime ~ 10¹⁰ years / M⁴

  where we measure masses in multiples of the mass of the Sun. We then have:

  • O star (20-40 M_sun): less than a million or so years
  • G star (~ 1 M_sun): 10 billion or so years

  We see O and B stars ===> star formation must be on-going in our galaxy, the Milky Way.

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Rate and Longevity of Star Formation

• Roughly, 4 M_sun of material goes into star formation every year (7 stars per year are thought to form in the Milky Way galaxy based on study of ₁₃Al²⁶ by Integral).
  • As stars evolve, they return roughly 1 - 2 M_sun per year back to the InterStellar Medium (ISM) ===> a net loss of gas from the Galaxy of roughly 2 or 3 M_sun per year. Currently, the ISM contains 10-15 % of the visible mass of the Milky Way ===> ten or so billion M_sun of gas and dust in the Milky Way galaxy--the materials out of which stars form.

    Star formation will persist in the Milky Way galaxy for billions or more years.

• What about the star formation rate? Has it been steady?

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Where does star formation occur? What are the Signatures of Star Formation?

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Basic Ideas of Star Formation

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