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Homework Help: Calculating Main Sequence Lifetime.

  1. Aug 22, 2008 #1
    1. Calculate the main sequence lifetime in years of a 10-M[tex]\odot[/tex] star if it has luminosity of 104L[tex]\odot[/tex] and 10% of its mass will be converted from hydrogen to helium in the core. What will the end state of this star be?

    Ok so I wasn't really sure what to put for working here as I have no idea where to begin, ive been searching around for a forumla or something to calculate the lifetime but my lecturers notes are very vague and not helpful at all and numerous different google searches haven't helped in giving me a straight answer.

    I found this formula somewhere but it doesn't make sense to me:


    Its part of a larger question involving the Hertzsprung Russell diagram which i've done however this bit im totally stumped, if any of you guys could point me in the right direction or explain it to me i'd really appreciate it.

    Oh and I should point out this is from a past paper, the only relevant information I could imagine is given to help on the front of the paper is (excluding the standards like planck / speed of light etc):

    Solar mass: 2x1030kg
    Solar Bolometric Luminosity: 3.9x1026W
  2. jcsd
  3. Aug 22, 2008 #2
    Ok so I used E=mc^2 and got the total energy of the converted material as 6x10^38J
    Which would sustain that luminosity for 5 years...

    Thats roughly the same answer I got from the equation in my original post but I thought it was wrong because 5 years seems waaaaay too short.

    Is that a plausible answer?
    Last edited: Aug 22, 2008
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