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I Did astronomers just lengthen the expected life of the Sun by 5 Gy?

  1. May 9, 2018 #1
    I had always thought that the Sun was about midway through its regular lifetime (i.e., before it becomes a red giant), but this article seems to say that instead of having another 5 Gy until then, it will be another 10 Gy.

    https://www.yahoo.com/news/scientists-sun-apos-death-even-164400014.html

    Either that or the author is clueless.
     
  2. jcsd
  3. May 9, 2018 #2
    The correct numbers:

    6.4 billion years from now the Sun's core runs out of hydrogen and so the Sun leaves the main sequence.
    7.1 billion years from now it becomes a red giant.
    7.8 billion years from now it becomes a white dwarf.

    The Sun's total lifetime from birth to white dwarfdom is 12.4 billion years. The frequently cited 10-billion number is just a round number, and I wish it would go away.

    Reference:

    Our Sun. III. Present and Future. I.-Juliana Sackmann, Arnold I. Boothroyd, and Kathleen E. Kraemer. Astrophysical Journal, 418, 457.
     
  4. May 9, 2018 #3

    Ken G

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    What's more, that article is not about any new discoveries about the future age of the Sun, nor even any discoveries about what will happen to the Sun. It has long been expected that the Sun would eject a significant fraction of its mass! All the article is about is whether or not what gets ejected will be visible by distant aliens as a "ghostly ring," or if it will be too dim to see. As often happens, whoever wrote the pop sci article completely missed the point of the research! There has been a recent theory that only stars with binary companions render their planetary nebulae visible by shepherding the mass into structures that are more easily viewed (and make quite pretty shapes). This research seems to suggest that although the shape of our Sun's planetary nebula won't be quite as pretty, it might still be rather visible. It's all about what it looks like, there are no new claims about what will happen or how long it will take. Why does every pop sci article have to claim that every new paper is some completely new paradigm, it must make the casual reader think astronomers are in a constant state of shock.
     
  5. May 24, 2018 #4
    I think the author must have confused the sun's total main sequence lifetime, for the time the sun has left before it leaves the main sequence.
     
  6. May 24, 2018 #5

    phinds

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    Much more likely the author just wasn't really paying attention and wrote something off in a hurry. That happens a LOT with science popularization.

    That is, he may in fact have had the confusion you attribute to him but not as confusion the way most us think of it but rather, he really didn't CARE. He saw some numbers and figured out how he could use them and wrote it off and ... all good to go, on to the next article (where he will do the same thing), let's just keep the pen moving.
     
  7. May 25, 2018 #6

    stefan r

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    The original paper had nothing to do with the sun. They looked at planetary nebula. They made models that include 10 billion year old systems. The model includes stars with 1 solar mass. The inverse article re-posted on yahoo has other problems too.

    The core will have lots of helium. The core will not have lost mass except mass lost as energy). The helium burns after the red giant stage. Shell hydrogen burning reignites in the AGB stage. The AGB stage ejects the elements that become a planetary nebula. The astronomy paper used oxygen III ions.
     
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