Time Needed for Life in Universe: M-Sun Weight & More

[Guarana]

Homework Statement

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.

Homework Equations

The Attempt at a Solution

I don't understand why some of that has to be true...

 

[DaveC426913]

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.

 

[Guarana]

Less m-Sun means longer lifespan, right?

 

[DaveC426913]

Are you guessing or are you researching?

 

[Guarana]

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.

 

[DaveC426913]

Check your figures. 25000 million years is longer than the universe has existed.

 

[Guarana]

Check your figures. 25000 million years is longer than the universe has existed.

Isn't Universe 13,8 bilion years old?

 

[DaveC426913]

Yes. And the number you wrote is 25 billion years.

 

[Guarana]

My apologies. I meant 2,5 bilions.

 

[mfb]

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.

 

[vela]

Check your figures. 25000 million years is longer than the universe has existed.

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.

 

[DaveC426913]

That's not really a problem, though, is it? It would just mean no low-mass stars have burned out yet in our universe.

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.