1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Life in universe

  1. Mar 14, 2015 #1
    1. The problem statement, all variables and given/known data
    For the development of life time is needed. The period during which the star remains at the main sequence depends primarily upon its mass. Type stars, our sun "yellow dwarf" remain on the main sequence about 10 billion years. Weight is often measured in multiples of the mass of the Sun called. M-Sun.

    Life on earth needed about 3.5 billion years to the local civilization could explore the universe, so if life anywhere else go to the same state, there must:

    a) Weight of stars to be less than about 1.3 m-Sun.

    b) Weight of stars to be less than about 3 m-Sun.

    c) Weight stars to be less than about 13 m-Sun.

    2. Relevant equations

    3. The attempt at a solution
    I don't understand why some of that has to be true...
    Last edited by a moderator: Mar 15, 2015
  2. jcsd
  3. Mar 14, 2015 #2


    User Avatar
    Gold Member

    Because the lifespan of a star is closely (and inversely) related to its mass.

    That should be a good push in the right direction to help you with the answer.
  4. Mar 14, 2015 #3
    Less m-Sun means longer lifespan, right?
  5. Mar 14, 2015 #4


    User Avatar
    Gold Member

    Are you guessing or are you researching? :wink:
  6. Mar 14, 2015 #5
    Researching! I think it's a, because if you have star with 0,8 m-Sun it stays on main sequence for 25000 milion years and that's close to 35000 - like us.
  7. Mar 14, 2015 #6


    User Avatar
    Gold Member

    Check your figures. 25000 million years is longer than the universe has existed.
  8. Mar 14, 2015 #7
    Isn't Universe 13,8 bilion years old?
  9. Mar 14, 2015 #8


    User Avatar
    Gold Member

    Yes. And the number you wrote is 25 billion years.
  10. Mar 14, 2015 #9
    My apologies. I meant 2,5 bilions.
  11. Mar 14, 2015 #10


    User Avatar
    2017 Award

    Staff: Mentor

    But 2.5 billion years is not the lifetime of a star with 0.8 solar masses...

    Stars with a smaller mass live longer, but I think the other direction is more relevant here.
  12. Mar 15, 2015 #11


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    That's not really a problem, though, is it? It would just mean no low-mass stars have burned out yet in our universe. 2.5 billion years, on the other hand, is a problem because it would be inconsistent with the lifetime of our Sun.
  13. Mar 15, 2015 #12


    User Avatar
    Gold Member

    Agreed. It's not a problem, it just doesn't help answer the question. The question is about the required minimum lifespan of a star to support life.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted