How do low mass stars outlive high mass stars?

In summary, the conversation discusses the lifespan of stars and the amount of hydrogen converted in the Sun over its lifetime. The book being used claims that the Sun has used less than 10% of its hydrogen, despite having another 5 billion years before it runs out of fuel. However, the core of the Sun is unable to bring fresh hydrogen from its outer layers, resulting in a limited amount of fuel for fusion. This is in contrast to less massive stars which are able to effectively move fused helium outside while bringing fresh hydrogen into the core, giving them longer lifespans of trillions of years. The comparison is made to redwood saplings, which can outlive their surroundings, and high-mass stars, which burn brightly but have
  • #1
Henry365
3
0
I'm just doing some reading on stars and I've hit a problem which I can't solve.

According to a book I'm using it claims the amount of hydrogen converted in the Sun over it's lifetime so far is 5.4x10^55. I roughly agree with this figure using the method this author calculates the number. He also says that the sun had about 8.9x10^56 hydrogen atom and so concludes the star has used less than 10% of it's hydrogen.

However it appears that most people say the sun has about another 5 billion years before it runs out of fuel and yet we've used less than 10& in about 4.7billion years? Can anyone explain the vast differences here?

Thanks.
 
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  • #2
The core of the sun, and stars similar to the sun, cannot bring fresh hydrogen from their outer layers into the core to replace the fused hydrogen. Thus whatever amount is in the fusible area of the core is all that it has to work with. Once this is used up the Sun will turn into a Red giant and begin burning Helium for a while.
 
  • #3
It;s interesting to study models of the sun like this Standard Solar Model. The core of the sun is already down to only 33% H, after starting at about 70% H.
 
  • #4
Just to contrast, while the Sun is unable to support convection (the process which would bring hydrogen from the outer envelope down into the core), less massive stars are. These stars are able to effectively move the fused helium outside, while bringing fresh hydrogen into the core, which is part of the reason why they can have such ridiculously long lifespans (trillions of years).
 
  • #5
Nabeshin said:
Just to contrast, while the Sun is unable to support convection (the process which would bring hydrogen from the outer envelope down into the core), less massive stars are. These stars are able to effectively move the fused helium outside, while bringing fresh hydrogen into the core, which is part of the reason why they can have such ridiculously long lifespans (trillions of years).

And to bounce off your post, these low mass stars also use their fuel much slower than the Sun. A red dwarf that's 49% of the Suns mass only has 3.5% of its luminosity.
 
  • #6
Nabeshin said:
Just to contrast, while the Sun is unable to support convection (the process which would bring hydrogen from the outer envelope down into the core), less massive stars are. These stars are able to effectively move the fused helium outside, while bringing fresh hydrogen into the core, which is part of the reason why they can have such ridiculously long lifespans (trillions of years).

Trillions? How do you figure that? The entire cosmos is only 13-14 billion years old at this point. What are these Methuselah stars?
 
  • #7
they WILL exist for trillions of years, they are currently not so old. At most 13.7 billion years old or so
 
  • #8
Phoenix59 said:
Trillions? How do you figure that? The entire cosmos is only 13-14 billion years old at this point. What are these Methuselah stars?

A redwood sapling you plant in a two day old park will likely outlive your great, great, great, great, great grandchildren despite the fact that the park is only two days old.

Similarly, low mass stars burn cool and slowly, live long lives and go out with a whimper while high-mass stars (much like many rock stars) live fast and furious, leave a big bloated corpse, and go out with a bang.
 

1. What does it mean for the sun to run out of hydrogen?

The sun is powered by a process called nuclear fusion, where hydrogen atoms combine to form helium. As the sun burns through its hydrogen fuel, it will eventually run out and this process will slow down, causing the sun to lose its energy and eventually die.

2. When is the sun expected to run out of hydrogen?

Based on current estimates, the sun has used up about half of its hydrogen and is expected to run out in approximately 5 billion years.

3. Will the sun's death affect life on Earth?

Yes, when the sun runs out of hydrogen, it will expand into a red giant, engulfing and destroying the inner planets, including Earth. However, this process is expected to take billions of years, so it is not an immediate concern.

4. Can we do anything to prevent the sun from running out of hydrogen?

No, the sun's life cycle is a natural process that cannot be altered or controlled by humans. However, scientists are researching ways to potentially prolong the sun's life using methods such as artificial fusion.

5. What happens after the sun runs out of hydrogen?

Once the sun has used up its hydrogen fuel, it will begin to fuse helium atoms, creating heavier elements and releasing energy. This process will continue until the sun runs out of all its fuel and eventually dies, becoming a white dwarf.

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