STAR FORMATION Chaisson & McMillan, Chs. 18 & 19

• 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 = (efficiency of energy production) x M_Sun x c².
    

  • How fast will the Sun burn this fuel?

    Fuel Consumption rate = Luminosity

    ===> lifetime = Fuel/Luminosity = (0.007x0.1)x2x10³⁰x(3x10⁸)/4x10²⁶ = 3.2x10¹⁷ s = 10¹⁰ years

    The Sun burns only the inner 10 % of its hydrogen during its main sequence lifetime.

  • In general, for Main Sequence stars,

    lifetime ~ 10¹⁰ years / M³

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

    • O star (20-40 M_sun): million or so years
    • G star (~ 1 M_sun): 10 billion or so years
    • M star (0.2 M_sun): 250 billion years >> age of the Universe

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

• Rate of Star Formation

  • Roughly, 3 - 4 M_sun of material goes into star formation every year. Because the average star is a little less massive than the Sun, it is believed that roughly 4 - 10 stars form every year in the Milky Way galaxy.

  • Type II Supernovas occur roughly every 50 years or so in our Galaxy and planetary nebulas form at a rate of roughly 1 per year in our Galaxy. These and other mechanisms return material to the ISM. This amounts to roughly 1 - 2 M_sun per year. ===> a net loss of gas from the Galaxy of roughly 1 - 3 M_sun per year. Currently, there are ~ 5 billion M_sun of gas and dust in the Milky Way galaxy--the materials out of which stars form.

    Star formation can persist in the Milky Way galaxy for several billion more years.

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

Locations where star formation occurs (Properties of the important players in star formation)

Basic ideas